Serum P4 Research Articles

Correlation Between Luteal Phase Serum Progesterone Levels and Pregnancy Outcome in Frozen Embryo Transfer Cycles: A Prospective Cohort Study

Objectives To study the correlation between luteal phase serum progesterone (P4) levels and pregnancy outcome in frozen embryo transfer (FET) cycles and to find out the cut-off level of luteal phase serum P4 which favours successful pregnancy outcome in FET cycles. Material and Methods This prospective cohort study included 100 women undergoing hormone replacement therapy (HRT)-FET cycle at Akanksha IVF Centre from December 2023 to June 2024, fulfilling the inclusion and exclusion criteria. Serum P4 levels were measured for all the patients in the luteal phase (days 21–23) after FET with intramuscular P4 as luteal phase support. Pregnancy outcome was assessed in terms of implantation rate, biochemical pregnancy rate, clinical pregnancy rate (CPR), first-trimester miscarriage rate and ongoing pregnancy rate. Results The most favourable pregnancy outcomes were observed at serum P4 levels 25.1-35 ng/mL. A statistically significant association was seen between the luteal phase serum P4 levels and implantation rate (36.08%), biochemical pregnancy rate (4%), CPR (52%) and ongoing pregnancy rate (42%). According to the receiver operating characteristic (ROC) curve analysis, the optimal cut-off value for favourable outcomes was determined to be 22.3 ng/mL. However, the analysis also indicated that the luteal phase serum P4 levels did not reliably predict clinical or ongoing pregnancy. Conclusion Larger studies are needed to establish a threshold level of serum P4 in the luteal phase that can differentiate between successful and unsuccessful implantation. However, it is still uncertain whether the issue of unsuccessful implantation can be resolved once it is detected on days 21–23 of the HRT-FET cycle.

Exogenous progesterone rescue in patients with low mid-luteal serum progesterone levels undergoing true natural vitrified-warmed blastocyst transfer.

To explore whether a 25mg subcutaneous progesterone daily rescue daily improves the reproductive outcomes in patients with low serum progesterone (P4) levels (7-10ng/mL), measured one day before true natural cycle (t-NC) frozen embryo transfer (FET). A cohort study of 192 women undergoing t-NC warmed blastocyst transfer. Patients were stratified into three different groups based on serum P4 levels on the FET-1day: patients who had serum P4 levels of 7-10ng/mL and underwent rescue progesterone administration (rescue group), patients with serum P4 levels of 7-10ng/mL without progesterone administration (non-rescue group), and patients with serum P4 > 10ng/mL on FET-1day (control group). The primary outcome was possible differences in live birth rate (LBR) between groups. The LBRs for the serum P4 7-10ng/mL without rescue, 7-10ng/mL with rescue, and > 10ng/mL (control) groups were 41%, 46%, and 52%, respectively (p = 0.61). The estimated adjusted probability of live birth for serum P4 7-10ng/mL without rescue, 7-10ng/mL with rescue, and > 10ng/mL (control) groups were also comparable: 43.5% (95% CI, 20.0-70.4%), 49.8% (95% CI, 28.1-71.6%), and 57.4% (95% CI, 44.0-69.8%), respectively. Serum P4 levels higher than 7ng/mL seem to secure LBRs in patients undergoing t-NC FET. A rescue policy consisting of a daily subcutaneous 25mg progesterone dose in patients with serum P4 levels 7-10ng/mL does not further enhance LBRs when compared to those patients with similar serum P4 levels without rescue.

Effects of exogenous progesterone on the ovine serum progesterone profile during the non-breeding season

Exogenous progesterone (PRG) sources are used to induce ovine estrus during the non-breeding season. Intramuscular injection (IM) of PRG is an uncommon route for this purpose. This study investigated serum progesterone (P4) levels after IM administration of 50 mg of two different PRG products. Ten ewes were selected and received two consecutive PGF2α injections at 24-h intervals. Serum samples were collected (Time 0), followed by the injection of single doses of Fertigest® or Vetagesterone®. Serum P4 levels were assayed at times (T) 0, 30 min, 3,6,12,24,48,72,96, and 120 h after injection. A large variation in the serum P4 levels at T0 was detected. The serum P4 level at T0 was 4.3 ng/mL, which is considerable for anestrus ewes, following PGF2α administration. The mean time to reach maximum serum P4 concentration was 5.8 h, with a mean concentration of 22.5 ng/mL. Serum P4 levels returned to basal values (T0) after 48 h. An increased P4 production rate (PR) was detected following PRG administration, which continued for 24 h. A single injection of PRG reduced the variety of serum P4 levels from 24 h onward. The two different PRG generated different serum P4 concentrations. This study indicates an unusual change in serum P4 levels in anestrus ewes following PGF2α administration. 48 h after 50 mg PRG injection, the plasma levels of P4 reached basal levels in anestrus ewes.

Higher serum progesterone level has no negative impact on live birth rate in frozen embryo transfer

Optimal synchronisation between the endometrium and the embryo is key to the success of frozen embryo transfers (FET). It is achieved by administering different doses of exogenous oestrogen and progesterone (P4). The negative impact of low levels of P4 on FET has been reported, but there is a lack of knowledge about which levels are most appropriate. We aimed to evaluate whether high serum P4 levels measured on FET day affect the probability of having a baby at home. This retrospective cohort study includes 7546 FET cycles performed with hormone replacement therapy (HRT) for artificial endometrial preparation. Patients were divided into three groups according to P level on FET day (ng/mL): P4 < 20(n = 6623), P4 ≥ 20–40 (n = 770) and P > 40 (n = 146). Female age was per group P4 < 20 = 38.7 ± 3.1, P ≥ 20–40 = 39.0 ± 3.0, and P4 > 40 = 38.1 ± 2.9 years old (p = 0.53). The group with the highest progesterone levels found lower ongoing pregnancy rates without statistical significance (56.3 % (P4 < 20) vs 56.8 % (P4 ≥ 20-<40) vs 51.4 % (P4 > 40); p = 0.5). Miscarriage rate was also higher, although not significantly: 16.2 % (P4 < 20) vs 15.0 % (P4 ≥ 20-<40) vs 18.0 % (P4 > 40) (p = 0.6). These findings were explored with an adjusted analysis. A higher, but not significant, odds of miscarriage was observed when P4 > 40 ng/ml, aOR = 1.14 (0.75–1.74) (p = 0.55) whereas no such association was found with P4 ≥ 20–40 ng/ml (aOR = 0.92 (0.74–1.15) (p = 0.46)). The probability of livebirth is similar when the patient was P4 > 40 (aOR = 0.77 (0.51–1.15) (p = 0.20)) than when P4 ≥ 20-<40 (aOR = 0.94 (0.79–1.11) (p = 0.47). In conclusion, women with elevated serum P4 levels on the day of FET after HRT do not find their probability of live birth impaired.

Effect of post-mating administration of ketoprofen on serum progesterone concentration and fertility in Akkaraman ewes.

A major cause of early embryonic losses is inadequate secretion of progesterone (P4) hormone due to luteal insufficiency in farm animals. Post-mating applications that directly or indirectly increasing serum P4 concentrations have a positive effect on fertility. The aim of this study was to investigate the effect of post-mating administration of ketoprofen on serum P4 concentration and fertility in Akkaraman ewes synchronized with a short-term protocol during the breeding season. Oestrus monitoring ewes after synchronization were hand-mated and randomly assigned to two equal groups (Ketoprofen vs. Control). Ewes in the ketoprofen group (KPG) (n = 40) were administered with ketoprofen (Rifen, Richter pharma, Austria) intramuscularly (im) at a dose of 3mg/kg on days 9 and 10 after mating. In the control group (CG) ewes (n = 40) were administered with saline im on the same days. Blood samples were collected from ewes in both groups at four different time points of post-mating days (9, 12, 15 and 18 days). The results showed that there were no statistical differences between the KPG and CG groups on fertility parameters; pregnancy rates (85% vs. 72.5%), lambing rates (100% vs. 100%), single birth rates (55.9% vs. 55.2%), multiple birth rates (44.1% vs. 44.8%), litter sizes (1.56 vs. 1.55). In pregnant ewes, serum P4 concentrations on day 18 (4.35 ± 0.34 ng/mL) in the KPG group were higher than (3.27 ± 0.27 ng/mL) in CG group (P < 0.05). It was concluded that post-mating ketoprofen administration have no significant effect on fertility, but significantly increased the serum P4 concentration on day 18 in pregnant ewes.

Neuregulin 1 Signaling Attenuates Tumor Necrosis Factor α-Induced Female Rat Luteal Cell Death.

The corpus luteum (CL) is a transient ovarian endocrine structure that maintains pregnancy in primates during the first trimester and in rodents during the entire pregnancy by producing steroid hormone progesterone (P4). CL lifespan, growth, and differentiation are tightly regulated by survival and cell death signals through luteotrophic and luteolytic factors, including the epidermal growth factor (EGF)-like factor family. Neuregulin 1 (NRG1), a member of the EGF family, mediates its effect through ErbB2/3 receptors. However, the functional role of NRG1 in luteal cells (LCs) is unknown. Thus, this study investigated the role of NRG1 and its molecular mechanism of action in rat LC. Our experimental results suggest a strong positive correlation between steroidogenic acute regulatory protein (StAR) and NRG1 expression in mid-CL and serum P4 and estrogen (E2) production. In contrast, there was a decrease in StAR and NRG1 expression and P4 and E2 production with an increase in tumor necrosis factor α (TNFα) expression in regressing CL. Further in vitro studies in LCs showed that the knockdown of endogenous Nrg1 promoted the expression of proinflammatory and proapoptotic factors and decreased prosurvival factor expression. Subsequently, treatment with exogenous TNFα under these experimental conditions profoundly elevated proinflammatory and proapoptotic factors. Further analysis demonstrated that the phosphorylation status of ErbB2/3, PI3K, Ak strain transforming or protein kinase B (Akt), and ErK1/2 was significantly inhibited under these experimental conditions, whereas the treatment of TNFα further inhibited the phosphorylation of ErbB2/3, PI3K, Akt, and ErK1/2. Collectively, these studies provide new insights into the NRG1-mediated immunomodulatory and prosurvival role in LCs, which may maintain the function of CL.

PSIV-29 Efficacy of a chute-side pregnancy test on early pregnancy determination in mature Rambouillet ewes

Abstract Distinguishing pregnant from non-pregnant ewes in early pregnancy allows for more efficient flock management by producers. While early pregnancy detection techniques like ultrasonography and hormone quantification are well established, these techniques are often not adaptable to field conditions or require specialized equipment and training. The objective of this study was to evaluate a validated bovine commercial on-farm pregnancy test on efficacy for detecting early pregnancy in distinct blood constituents of ewes. Rambouillet ewes [n = 30; average body weight (BW) = avg 60.9 ± 1.1 kg; age 2 to 8 yr) were estrous synchronized using a 5 d CIDR protocol followed by 2 injections of PGF2α at 0 and 4 h. A rattle-painted ram was subsequently placed with ewes for a 35-d breeding season. Blood constituents including whole blood (WB), plasma (PL), and serum (SE) were collected via jugular venipuncture prior to synchronization (d 0) and on d 20, 35, and 70 after breeding. Blood constituents were individually evaluated using the IDEXX Alertys OnFarm pregnancy test for pregnancy detection. Trans-abdominal ultrasonography was performed on d 35 and d 70 post-breeding. Serum progesterone (P4) was quantified on d 100 of gestation to confirm pregnancy status. Progesterone concentrations ≥ 4 ng/mL were considered pregnant. On d 20 of gestation, IDEXX tests agreed with P4 concentrations on d 100 (χ2 = 0.30) in WB, SE and PL at 35.7, 53.6, and 53.6%, respectively. Pregnancy detection accuracy increased on d 35 of gestation as IDEXX tests agreed with P4 at d 100 (χ2 = 1.00) in WB, SE, and PL at 60.7, 60.7 and 60.7% accuracy, respectively. On d 70 of gestation, IDEXX tests agreed with P4 at d 100 (χ2 = 0.81) in WB, SE, and PL at 90.7, 93.3 and 93.3% accuracy, respectively indicating similarity in pregnancy diagnosis in the two methods. Detection of pregnancy using ultrasonography at d 35 identified 33% of pregnant ewes, while d 70 ultrasound detected 93% of pregnant ewes when compared with d 100 serum P4. Results suggest that the IDEXX pregnancy test provides early diagnosis of pregnancy with d 70 results comparable to d 100 serum P4 quantification regardless of blood constituent type.

Exogenous estrogen partially rescues progesterone deficiency and autophagosome enlargement in Mcoln1 −/− mouse model with lysosomal storage disorder

Objective: Female Mcoln1 −/− mice exhibit progressive progesterone (P4) deficiency, luteal cell degeneration, and premature embryo implantation failure at five months old. We attempted to rescue embryo implantation in non-virgin Mcoln1 −/− mice (5–6 months old) with exogenous P4 treatment on days 1.5 post-coitum (D1.5), D2.5, and D3.5, and observed partially restored luteal cell morphology on D4.5, but unexpectedly found 17β-estradiol (E2) contamination in the P4 working solution. In this study, we aim to investigate exogenous P4 and/or E2 for the partial recovery of luteal cell morphology in infertile Mcoln1 −/− mice. Methods: Control and non-virgin Mcoln1 −/− mice (5–6 months old) were treated with newly ordered vehicle, P4, E2, or P4+ E2 on D1.5 and D2.5 and dissected on D3.5 for P4 and E2 measurements, ovary histology, immunofluorescence, lipid droplet staining, and transmission electron microscopy. Results: E2 treatment significantly increased serum P4 levels in D3.5 Mcoln1 −/− mice. E2 and P4+E2 treatments, but not P4 treatment alone, largely improved the morphology of D3.5 Mcoln1 −/− corpora lutea, indicated by a more contiguous web-like collagen IV expression pattern, increased heat shock protein 60 expression, and reduced accumulation of large lipid droplets. Transmission electron microscopy revealed extremely enlarged autophagosomes and lipid droplets, lysosomes with lamellar structures, and mitochondria with reduced cristae in vehicle-treated D3.5 Mcoln1 −/− luteal cells, while in E2-treated D3.5 Mcoln1 −/− luteal cells, extremely enlarged autophagosomes and lipid droplets were reduced, indicating improved luteal cell ultrastructure. Conclusion: These findings reveal protective effects of high levels of exogenous E2 on P4 production and lysosomal function in Mcoln1 −/− luteal cells.

Preovulatory progesterone levels are the top indicator for ovulation prediction based on machine learning model evaluation: a retrospective study

BackgroundAccurately predicting ovulation timing is critical for women undergoing natural cycle-frozen embryo transfer. However, the precise predicting of the ovulation timing remains challenging due to the lack of consensus among different clinics regarding the definition of this significant event.ObjectiveTo compare the effectiveness of preovulatory serum progesterone levels (P4) versus luteinizing hormone levels (LH) in predicting ovulation time using two machine learning models.Methods771 patients who underwent autologous natural cycle-frozen embryo transfer between January 2015 and February 2022 were recruited. Utilizing variables including follicle diameters, preovulatory serum levels of LH, E2, and P4, two machine learning models were constructed to predict the ovulation time, the importance of the variables in predicting ovulation timing was further ranked.ResultsTwo machine learning models have the capability to accurately predict the timing of ovulation, specifically within 72, 48, or 24 h. The overall accuracy rates of the validation dataset, as determined by the classification trees and random forest models, were found to be 78.83% and 85.28% respectively. Notably, when predicting ovulation within 24 h, the accuracy rate of P4 ≥ 0.65ng/ml exceeded 92%. Furthermore, it was important to consider LH or E2 levels in conjunction with P4 when assessing ovulation timing in cases where P4<0.65ng/ml.ConclusionsPreovulatory serum P4 levels are better predictors of ovulation timing than LH levels and could be used as an alternative in clinical settings, and the model we developed can be used to pinpoint the day of ovulation. Ongoing research and advancements in technology are anticipated to enhance and refine the ovulation method.

Integrated Transcriptomic-Metabolomic Analysis Reveals the Effect of Different Light Intensities on Ovarian Development in Chickens.

Light is a key environmental factor regulating reproduction in avians. However, the mechanism of light intensity regulating ovarian development is still unclear. In this study, 5-week-old (5 wk) partridge broiler breeders were randomly divided into a low-light-intensity group (LL group) and a natural-light-intensity group (NL group) (n = 100). In the rearing period (5 wk to 22 wk), the light intensity of the LL group and NL group were 0.41 ± 0.05 lux and 45.39 ± 1.09 lux, and in the laying period (23 wk to 32 wk) they were 23.92 ± 0.06 lux and 66.93 ± 0.76 lux, respectively. Samples were collected on 22 wk and 32 wk. The results showed that the LL group had a later age at first egg and a longer laying period than the NL group. Serum P4 and LH levels in the LL group were higher than in the NL group on 22 wk (p < 0.05). On 32 wk, P4, E2, LH and FSH levels in the LL group were lower than in the NL group (p < 0.05). Ovarian transcriptomics and metabolomics identified 128 differentially expressed genes (DEGs) and 467 differential metabolites (DMs) on 22 wk; 155 DEGs and 531 DMs on 32 wk between two groups. An enrichment analysis of these DEGs and DMs identified key signaling pathways, including steroid hormone biosynthesis, neuroactive ligand-receptor interaction. In these pathways, genes such as CYP21A1, SSTR2, and NPY may regulate the synthesis of metabolites, including tryptamine, triglycerides, and phenylalanine. These genes and metabolites may play a dominant role in the light-intensity regulation of ovarian development and laying performance in broiler breeders.

Effect of post-mating GnRH or TAK-683 (Kisspeptin analog) treatment on the reproductive performance and serum progesterone concentration in ewes during the non-breeding season

This study was designed to evaluate the effect of post-mating GnRH or TAK-683 (kisspeptin analog) treatment on serum progesterone (P4) concentrations and fertility parameters of ewes during the non-breeding season. One hundred and twenty multiparous, lactating Awassi ewes were used. For estrus synchronization, vaginal sponges containing 60 mg of medroxyprogesterone acetate (MAP) were inserted into the vagina and kept there for nine days. On the day of sponge removal (day 0), 500 IU of eCG and 75 µg of d-cloprostenol were given intramuscularly. Rams were introduced in the flock 24 h after sponge removal and kept with the ewes for 26 days, allowing a second mating period after synchronized estrus. On the fourth day after mating (day 6) the ewes mated by the rams between the 24th and 72nd hours (n = 105) were randomly divided into three groups. Control group (n = 36) received 1 ml of saline solution subcutaneously; GnRH group (n = 34) received 4 μg of buserelin acetate intramuscularly; TAK-683 group (n = 35) received 5 μg of TAK-683 acetate subcutaneously. Blood samples were taken to measure serum P4 concentrations (ng/ml) at sponge insertion and on the 6th, 9th, 12th, 15th, 19th, 35th, and 50th days after sponge removal. Pregnancy diagnosis was conducted via serum P4 concentration measurement on the 19th day and transrectal ultrasonography on days 35 and 50. The results showed that GnRH treatment (4.823 ± 0.238; 2.151 ± 0.272) increased (P<0.05) the mean P4 concentration (ng/ml) in pregnant and non-pregnant ewes during the first mating period compared to Control (3.708 ± 0.207; 1.515 ± 0.164), while TAK-683 treatment (4.457 ± 0.181; 1.967 ± 0.213) was not different between groups. GnRH (58.82 %) and TAK-683 (42.10 %) treatments increased the pregnancy rate in the second mating period in comparison to the Control group (17.39 %) (P<0.05). Cumulative pregnancy and fecundity rates were higher in GnRH (79.41 %; 120.58 %) and TAK-683 (68.57 %; 100.0 %) groups than in the Control group (17.39 %; 58.33 %) (P<0.05). There was no difference in late embryonic loss rate among the groups (P>0.05), whereas early fetal loss rate tended to be lower in the TAK-683 (0 %) and GnRH (0 %) groups than in the Control group (15.38 %) (P=0.07). The total pregnancy loss rate (from day 19 to day 50 post-mating) was lower in GnRH (0 %) and TAK-683 (0 %) groups relative to the Control group (21.42 %) (P<0.05). There were no statistical differences among the groups in terms of the first mating period pregnancy rate, twinning rate, and litter size (P>0.05). As a result, treatment with GnRH and TAK-683 on the fourth day after mating increased fecundity in lactating ewes outside the breeding season by preventing total pregnancy losses (from day 19 to day 50) and increasing second mating pregnancy rates.

The natural menstrual cycle revisited – can natural cycle be trusted

BackgroundThe serum progesterone (P4) level during the luteal phase (LP) plays a crucial role in the initiation and maintenance of pregnancy. However, it is unclear whether the natural cycle consistently provides the best endocrine profile and whether mid-luteal serum P4 levels are always sufficient to support implantation and early pregnancy. The question has become more relevant in relation to fertility treatment, as more frozen embryo transfer cycles are performed in the natural cycle. Moreover, can serum hormone levels and covariates measured during the follicular phase (FP), such as Follicle Stimulation Hormone (FSH), Luteinizing Hormone (LH), Estradiol (E2), Anti-Mullerian Hormone (AMH) and Antral Follicle Count (AFC), be used to predict P4 levels during the luteal phase (LP)?ResultsThis observational prospective cohort study analysed 26 healthy women with a cycle length between 21–35 days and a body mass index (BMI) < 30 kg/m2. Blood sampling started on the fifth day of the menstrual cycle and continued every fifth day until the next cycle. The procedure was repeated for a total of three cycles. The study found that only ten women had a P4 level greater than 30 nmol/L on cycle day 20 or 25 in all three cycles. In total, only 45 cycles out of 77 cycles had serum P4 levels ≥ 30 nmol/L.The E2 level ≥ 345 pmol/L on cycle day 10 proved to be predictive of a P4 level of ≥ 30 nmol/L on either day 20 or day 25 with a sensitivity of 57% and a specificity of 89%. No other covariates, including the FSH level cycle day 5, LH levels during the follicular phase, age, weight, AFC and AMH cycle day 5 correlated with LP P4 levels.ConclusionsA significant correlation between FP E2 levels cycle day 5 (> 131pmol/L) and cycle day 10 (> 345pmol/L) and a LP P4 level ≥ 30 nmol/l was found; thus, the FP E2 level is a predictor of corpus luteum competence. Our findings highlight the existence of suboptimal P4 levels during the LP and a significant inter-individual and intra-cycle variation in P4 levels during the LP in regular menstruating women.

P-285 Serum progesterone level may not impact ongoing pregnancy rate (OPR) in patients with endometriosis undergoing frozen-warmed-blastocyst transfer employing hormone replacement treatment (HRT) with subcutaneous progesterone

Abstract Study question Do serum progesterone (P4) levels on frozen embryo transfer (FET)-1 day impact OPRs in patients with endometriosis undergoing HRT-FET with subcutaneous progesterone (sc P)? Summary answer In HRT cycles employing sc P, serum P4 levels on FET-1 day do not affect OPRs in patients with or without endometriosis. What is known already In HRT-FET cycles employing vaginal P, reproductive outcomes are improved by serum P4 monitoring and employing a rescue protocol, if needed. However, there is paucity of data for the need of serum P4 monitoring in HRT cycles employing sc P. Endometriosis is associated with P4 resistance. There is only one study evaluating the impact of serum P4 levels on reproductive outcomes in patients with endometriosis; in this study lacking a control group and employing vaginal P gel 90 mg/12 hours supplemented by daily 50 mg intramuscular P, a threshold of 37.1 ng/ml has been reported for improved live birth rates. Study design, size, duration Retrospective cohort study. 451 consecutive patients undergoing their first HRT- vitrified warmed blastocyst transfer during November 2021-June 2023 at Anatolia IVF Centre were included. 44 patients had endometriosis with surgical and/or ultrasound findings and the remaining 407 patients did not harbor endometriosis. The presence of adenomyosis was an exclusion criterion. Following 10-12 days of 6 mg/day estradiol valereate use, sc P 25 mg/12hours (Prolutex, Ibsa) was administered. The primary outcome measure was OPR. Participants/materials, setting, methods Serum P4 levels were measured 4-5 hours after morning administration of sc P on FET-1 day. The impact of serum P4 on OPRs was assessed at various percentiles adjusting for female age, body mass index, prior birth, preimplantation genetic testing for aneuploidy, number/grade of blastocysts transferred. Multivariate regression models were performed in the whole cohort incorporating polynomial P4 terms and endometriosis interactions; optimal model for OPR prediction was selected using the lowest Akaike Information Criteria. Main results and the role of chance Patients with (27/44, 61.4%) and without (214/407, 52.6%) endometriosis had comparable OPRs. In the endometriosis group, the 10th, 50th, and 90th percentiles of serum P4 were 15.6, 25.1, and 35.4 ng/ml, respectively, compared to 14.9, 23.5, and 35.6 ng/ml in the non-endometriosis group. In the endometriosis group, the OPRs were 60.0%, 66.7%, 56.3%, and 60.0% for the &amp;lt;10p, 10-50p, 50-90p, &amp;gt;90p groups, respectively. These figures were 46.3%, 50.3%, 56.8%, and 51.2%, in the non-endometriosis group, respectively. In the endometriosis group, taking the 50-90p group as the reference, the adjusted odds ratios (aORs) for OPR of &amp;lt; 10p, 10-50p, and &amp;gt;90p groups were 1.24 [0.03, 50.45], 1.77 [0.31, 10.24], and 2.08 [0.05, 80.23], respectively. In the non-endometriosis group, the respective aORs were 0.85 [0.40, 1.79], 0.80 [0.49, 1.29], and 0.72 [0.34, 1.50]. In the multivariate regression analysis to determine the optimal model, neither serum P4 levels (aOR for linear term: 1.11 [0.98, 1.26]; for quadratic term: 0.998 [0.996, 1.00]) nor the diagnosis of endometriosis (OR: 1.48 [0.74, 2.98]) significantly predicted ongoing pregnancy after adjusting for confounders. Additionally, the optimal model did not include the interaction term, suggesting that endometriosis does not significantly modify the impact of serum P4 levels on OPRs. Limitations, reasons for caution The study’s limitations include retrospective study design, a limited sample size of the endometriosis cohort, absence of laparoscopy for endometriosis exclusion in the non-endometriosis group, and lack of data on endometriosis phenotypes. Wider implications of the findings In HRT-FET cycles employing sc P 25 mg/12hours neither serum P4 nor the presence of endometriosis have an impact on OPRs. Endometriosis may not modify the impact of serum P4 on OPRs suggesting a lack of P resistance in such cycles or the overcoming of P resistance by this regimen. Trial registration number not applicable

P-653 Impact of dydrogesterone use in cycles with low progesterone levels on the day of frozen embryo transfer

Abstract Study question Assessing if Frozen Embryo Transfer (FET) outcomes in hormonal replacement treatment with dydrogesterone (DYD) for low progesterone levels match those with normal progesterone (P4) values Summary answer The live birth rate showed no significant difference between patients with low and normal serum P4 levels in FET, utilizing DYD as rescue therapy What is known already The number of IVF/ICSI cycles and frozen embryo transfers (FET) is increasing. The preparation for FET can occur in natural or artificial cycles, showing no significant differences in clinical pregnancy and live birth rates. Artificial cycles involve exogenous estradiol supplementation, starting after menses, and progesterone (P4) addition post-endometrial proliferation. Numerous studies consistently indicate that diminished P4 levels are correlated with inferior outcomes in hormonal replacement treatment, showing a potential decrease of up to 30% in ongoing pregnancy rates. Despite a suggested rescue strategy, evidence supporting its efficacy using an oral route is insufficient. Study design, size, duration This was a retrospective cohort study, of single embryo transfers (SET) from FET cycles conducted between July 2019 and March 2022, after artificial endometrial preparation with valerate-estradiol and micronized vaginal P4. In cases of low serum P4 (up to 12,5ng/dl) on the planned transfer day, 10 mg of dydrogesterone (DYD) three times daily was added. Solely blastocyst single embryo transfers (SET) were included. The primary endpoint was the live birth rate&amp;gt; 24 weeks. Participants/materials, setting, methods 535 FET-SET cycles were analyzed. Patients with an endometrial layer thinner than 7 mm, endocavitary pathology or serum P4 values&amp;lt; 4ng/dl were excluded. The explanatory variables evaluated were: relevant female characteristics, previous IVF/ICSI cycle and relevant FET cycle parameters (endometrial thickness, serum P4 value on the FET day, days in culture before blastocyst freezing) and use of DYD as rescue therapy. Statistical analysis was performed using IBM®SPSS® statistics v22.0 and R4.2.2 for Windows. Main results and the role of chance Out of the 535 FET cycles analyzed, 136(25.4%) underwent treatment with DYD. There were 337 pregnancies (63%), 207 live births (38.6%) and 130 miscarriages (38.5%). Serum P4 varied from 4.2-32.3 ng/dl, with an average of 14.93 ng/dl (SD 4.52). The best model to explain serum P4 distribution considered a gamma distribution for P4. Female age on the FET day, female ethnicity and female weight seemed to explain P4 variation. A sensitivity analysis on the P4 values was performed. The data were divided into 5 groups according to P4 levels and the rate of live birth per quintile was evaluated. There were no statistically significant differences between the groups. Patients with low P4 which had DYD added had no statistical differences regarding deliveries, 40% vs 36% (p = 0,354). The multivariable model revealed that older females at pick up, a thinner endometrial measure and transferring a day 6 blastocyst were negativey associated with live birth (p &amp;lt; 0,05), but not P4 levels or medication with DYD. A sub-group analyses was performed according to the median value of P4 (9.6 ng/ml) of those to whom DYD was added. No statistically significant differences were identified for biochemical pregnancy 59% vs 60% (p = 1) and live birth rate 34%vs38% (p = 0,653). Limitations, reasons for caution This retrospective study lacks an untreated control group, causing inherent heterogeneity. It’s unclear if there’s an upper limit for P4 levels to restrict DYD supplementation or a minimum level rendering this strategy unsuitable. Monitoring DYD’s fetal/neonatal safety is imperative. Wider implications of the findings The supplementation with oral DYD in hormonal replacement FET cycles is an easy and cheap strategy in patients with for low P4 levels. The duration of DYD administration should be further evaluated. Trial registration number not applicable

P-429 Measuring serum progesterone levels on the day of a fresh blastocyst transfer is debatable as there is no evidence for correlation with ongoing pregnancy results

Abstract Study question Does serum progesterone (P4) level on the day of a fresh blastocyst transfer relate to ongoing pregnancy rate (OPR)? Summary answer OPR after a fresh single blastocyst transfer seems not to be associated with serum P4 level on the day of transfer. What is known already Several studies have suggested an optimal serum P4 threshold for embryo transfers in frozen embryo transfer cycles. However, for fresh embryo transfers, data are scarce and conflicting. Study design, size, duration A retrospective single-center cohort study was performed on 598 complete data cycles, retained out of 631 consecutive fresh single blastocyst transfer cycles. Data were collected from patients undergoing a fresh IVF/ICSI cycle with autologous oocytes at a tertiary fertility center between June 2022 and August 2023. Participants/materials, setting, methods A total of 482 unique patients underwent one or more single fresh blastocyst transfers using micronized vaginal progesterone (MVP) 800mg BID for luteal phase support starting day after oocyte retrieval. Serum P4 levels were determined on day of transfer. The primary endpoint was OPR, positive hCG-test and early pregnancy loss (EPL) were secondary endpoints. Unadjusted and adjusted generalized estimating equations (GEE) assessed P4 level association with the endpoints, using an exchangeable working correlation matrix. Main results and the role of chance No association was identified between P4 levels on day of transfer and OPR after accounting for maternal age, blastocyst quality, P4 and estradiol level at last ultrasound, BMI and endometrial thickness. Data were grouped according to 10/50/90 and 25/50/75 percentiles, resulting in groups &amp;lt; = or &amp;gt; 27ng/ml and &amp;lt; = or &amp;gt; 40ng/ml, with omission of 90th and 75th percentile groups due to right-skewed distribution. With serum P4 levels higher than 40ng/ml, the probability of a positive hCG-test significantly increased (OR 1.79, CI 1.11-2.91; p = 0.018). No significant difference was observed in patients with serum P4 &amp;lt; = or &amp;gt; 27ng/ml (OR 1.23, CI 0.66-2.30; p = 0.506). Regarding OPR, no significant differences were observed when comparing patients with serum P4 &amp;lt; = or &amp;gt; 27/ng/ml or &amp;lt; = or &amp;gt; 40ng/ml (OR 0.88, CI 0.42-18.85; p = 0.736 and OR 1.41, CI 0.83-2.37; p = 0.203, respectively). Moreover, EPL did not significantly differ between serum P4 level groups (OR 1.93, CI 0.61-6.13; p = 0.265 and OR 1.2, CI 0.51-2.84; p = 0.674). Age (p &amp;lt; 0.001) and embryo quality (p &amp;lt; 0.001) are significantly related with OPR. Additionally, late follicular progesterone levels and OPR are significantly associated (OR 2.39, CI 1.16-4.95 in patients with P4 &amp;lt; = or &amp;gt; 27/ng/ml and OR 2.21, CI 1.07-4.55 in patients with &amp;lt; =40ng/ml and &amp;gt;40ng/ml). Limitations, reasons for caution Limitations include the retrospective design and the lack of live birth outcome data. Progesterone levels exceeding 60 ng/ml were not further analyzed to their precise value but grouped as 60 plus which did not allow to identify potential detrimental effects of very high P4 levels on treatment outcome. Wider implications of the findings Our data suggest that measuring P4 on the day of a single blastocyst transfer with MVP luteal phase support may not be indicative of OPR or the risk of EPL. This raises questions regarding the necessity for routine P4 measurements as well as the development of rescue strategies. Trial registration number ONZ-2023-0628

P-626 Progesterone rescue is effective for clinical pregnancy outcome in women presenting low circulating progesterone levels at frozen embryo transfer day

Abstract Study question Is subcutaneous progesterone (prolutex® 25mg daily) addition effective for clinical pregnancy outcome in women presenting low progesterone(P4) levels at frozen embryo transfer(FET) day? Summary answer Subcutaneous progesterone rescue improved ongoing pregnancy rate and clinical pregnancy rate in women with low P4 results at FET day. What is known already FET has been increased, because preimplantation genetic testing for aneuploidies is performed widely, and FET presents a significantly low risk of ovarian hyperstimulation syndrome.In FET, there is no established optimal protocol for preparing endometrium, but hormonal replacement therapy (HRT) is widely used due to its convenient schedule adjustment. HRT protocol induce anovulation, functioning corpus luteum is lacking and exogenous progesterone administration is very important. Therefore, women showing low P4 levels around FET day have lower pregnancy rate. However, there are currently no data on the effectiveness of progesterone rescue. Study design, size, duration Primary outcomes from a randomized cohort retrospective study investigating subcutaneous progesterone (prolutex® 25mg) daily addition for whom had low P4 levels (&amp;lt;12ng/mL) at FET day. The study was conducted at one infertility center in Korea from January 2022 to December 2023 and pregnancy outcomes of FET transfers registered until Oct. 2023,. 194 patients fulfilled the inclusion criteria. Participants/materials, setting, methods One hundred ninety four women divided into two groups based on progesterone levels, with 12ng/ml as the threshold. Under 12ng/mL group were randomized to subgroup with and without addition of subcutaneous progesterone. In total 278 FET cycles, the effect of progesterone rescue on cumulative clinical pregnancy rate (CPR), Ongoing pregnancy rate (OPR) was reported as primary outcomes. Main results and the role of chance In total 278 cycles, there were 137 cycles with adequate serum P4 levels, while 141 cycles presented with low P4 levels in which randomly rescue subcutaneous progesterone administration added from next day of embryo transfer. When comparing the groups, there was no statistical difference in maternal age, BMI, smokers, duration of infertility, type of infertility, indication of in vitro fertilization(IVF), endometrial preparation method. In low P4 group, with and without subcutaneous progesterone addition subgroups included 51 and 90 cycles, retrospectively. CPR were 52.9% versus 35.6% (P = 0.044; chi-squared test) with a statistically significant higher rate of OPR in progesterone rescue group (45.1% versus 28.9%, p = 0.052). When comparing the group with adequate P4 levels and the group with low P4 levels without progesterone rescue, OPR were 18.2% versus 28.9% (p = 0.06, chi-squared test), CPR was significantly higher in low P4 levels group (23.4% versus 35.6%,p=0.046, chi-squared test). Adequate P4 level group had more IVF attempts (4.6 versus 2.2, p &amp;lt; 0.001, chi-squared test). There is tendency to use more luteal phase support medication with repeated attempt (serum P4 concentration on ET day 39.3 ng/mL versus 8.7 ng/mL, p &amp;lt; 0.001, t-test) Limitations, reasons for caution The main limitation of the study was retrospective, and had small sample size. A control group without progesterone rescue in low P4 levels did not receive any intervention. Wider implications of the findings The progesterone rescue for women presenting low P4 on FET day improved clinical outcome and excessively raising progesterone medication may have adverse effects. Therefore rather than using excessive progesterone administration from luteal support start day, progesterone rescue might be effective when low P4 levels presenting at FET day. Trial registration number not applicable

P-418 What is the optimal midluteal phase circulating progesterone level during a fresh IVF cycle? The answer differs from what one expects in a natural cycle

Abstract Study question Do midluteal phase circulating progesterone (P4) levels relate to the fresh embryo transfer clinical outcome and is rescue P4 useful in such cases? Summary answer Live birth rate (LBR) was significantly lower when P4 levels were below 20ng/ml and did not seem to benefit from rescue intramuscular P4. What is known already Preceding literature on the predictive value of midluteal P4 for LBR has shown conflicting results and frequently included small sample sets and heterogeneous ovarian stimulation protocols. The findings reported ranged from the lack of an association between P4 serum levels and clinical outcome to worse success rates seen either in the groups with the highest or the lowest P4 in midluteal phase. Furthermore, while rescue P4 has been empirically proposed, it has lacked formal assessment thus far. Study design, size, duration In total, 652 patients who underwent a fresh single blastocyst transfer in an IVF cycle in our center between 2014 and 2021 were included in this retrospective cohort study. All were GnRH-antagonist cycles using hCG trigger and luteal support with micronized vaginal progesterone 200mg twice daily. Rescue intramuscular progesterone was systematically administered whenever low midluteal P4 (below 1 standard deviation of the center’s mean) levels were detected. Participants/materials, setting, methods The cycles were subdivided into three groups according to the midluteal P4 levels: &amp;lt;10ng/ml, 10-20ng/ml and &amp;gt;20ng/ml. The primary outcome assessed was LBR, with secondary outcomes including clinical pregnancy (CPR) and pregnancy loss rates. Maternal age and body mass index (BMI), year of treatment, ovarian response, endometrial thickness, cause of infertility and embryo quality were controlled for using multivariable logistic regression. Main results and the role of chance The mean age ± standard deviation of patients was 36.8±3.8 years, while mean weight and BMI were 63.2±11.5kg and 23.3±3.9kg/m2, respectively. LBR in the group with P4&amp;gt;20ng/ml (46.5%) was significantly higher than in the groups with low and intermediate P4 serum levels (23.1% and 28.1%, respectively, p &amp;lt; 0.001). The same was true for CPR (54.5%, 30.8% and 37.9%, respectively, p &amp;lt; 0.001). Conversely, the rate of pregnancy loss in the group with P4&amp;gt;20ng/ml (23.8%) was significantly lower than in the groups with low and intermediate P4 levels (42.6% and 37.5%, respectively, p = 0.018). The multivariable logistic regression confirmed that, after controlling for the confounding variables described above, P4&amp;gt;20ng/ml remained significantly associated with a higher LBR (OR: 2.285; 95% CI: 1.506-3.469) and a lower pregnancy loss rate (OR: 0.488; 95% CI: 0.273-0.873), irrespective of the use of rescue IM P4. Finally, a multivariable linear regression analysis of the patients baseline characteristics suggested that the only parameter predictive of midluteal P4 levels was the female patients’ weight, with an inverse relationship (adjusted regression coefficient: -0,012; 95% CI: -0,016/-0,009). Limitations, reasons for caution As the pituitary suppression, ovulation trigger and luteal support protocols used in the cycles included in the study were homogeneous (in order to maximize the internal validity of the results), this limits the extrapolibility of the results to other stimulation protocols. Furthermore, we caution that this is a retrospective study. Wider implications of the findings The usefulness of both midluteal P4 serum measurements and rescue P4 should continue to be assessed. The reasons behind the need for higher levels of P4 in a fresh cycle, when compared to natural cycles, must also be investigated. Luteal support may require personalization according to female body weight. Trial registration number Not Applicable

P-437 Are serum progesterone levels predictive for reproductive outcomes in artificial cycles if individualized luteal phase support is only administered when progesterone is below 5 ng/ml?

Abstract Study question Do serum progesterone levels predict reproductive outcomes in artificial cycles when individualized luteal phase support is administered only if progesterone falls below 5 ng/ml? Summary answer The low 5 ng/ml progesterone threshold appears to be sufficient for the patient not to require additional progesterone injections when progesterone is above 5 ng/ml. What is known already Serum progesterone (P4) level is negatively associated with ongoing pregnancy rate (OPR) and miscarriage rate in artificially prepared frozen embryo transfer (FET) cycles using standard micronized vaginal progesterone (MVP) for luteal phase support. Individualized luteal support is considered a successful rescue strategy in cycles with low serum progesterone levels eliminating the effect of P4 levels on outcome. Cut-off levels for this rescue strategy range from 8.8 to 10 ng/ml. Study design, size, duration A retrospective single-centre cohort study including a total of 1,016 vitrified-warmed single blastocyst transfers performed at a tertiary fertility centre between October 2021 and December 2022. Blastocysts of ≥ 3CC Gardner score were eligible for vitrification on day 5 or day 6 (Vit-kit or Vit-kit NX, FuijiFilm). Embryos were warmed and subsequently transferred on the same day which was day 5 in the cycle, regardless if the embryo was vitrified on day 5 or day 6. Participants/materials, setting, methods We included 595 patients undergoing an artificially prepared embryo transfer (ET) cycle using MVP 800mg BID for luteal phase support. Serum P4 levels were determined on the day of ET with the initiation of additional injections of subcutaneous P4 from the day after ET in patients with P4 &amp;lt; 5ng/ml. Primary endpoint was OPR. Multivariable logistic regression was performed to correct for confounders. Generalized estimating equations (GEE) models were fitted for primary and secondary outcomes. Main results and the role of chance OPR was comparable for the 3 groups: 9/40 (22.5%) for patients with P4 &amp;lt;5ng/ml, 64/275 (23.3%) for patients with P4 5-10 ng/ml and 181/701 (25.8%) for patients with P4 &amp;gt;10ng/ml (p = 0.377). No significant association between P4 category and likelihood for OPR was found after adjusting for confounders. Early clinical miscarriage rate was significantly different between the 3 groups: 5/40 (12.5%) in patients with P4 &amp;lt;5ng/ml, 26/275 (9.5%) with P4 5-10ng/ml and 37/701 (5.3%) with P4 &amp;gt;10ng/ml (P = 0.005). Limitations, reasons for caution Higher clinical miscarriage rate in cycles with a P4 level under 10 ng/ml questions the efficacy of rescue progesterone in cycles with a low P4. The patient population also exists of a subgroup of PGT-a tested cycles which was not included as a potential confounder in this analysis. Wider implications of the findings The 5 ng/ml P4 threshold appears to be sufficient for the patient not to require additional P4 injections when P4 is above 5 ng/ml. Consequently, a significantly lower proportion of cycles would need to be supplemented with rescue progesterone; 3.8% versus 31.3% for the 10 ng/mL cut off. Trial registration number ONZ-2023-0223

P-672 Is there a sweet spot for follicular size and/or estradiol level for the initiation of micronized progesterone to optimize natural proliferative phase (NPP) cryo-cycle outcome?

Abstract Study question Is there an optimal follicular size and/or estradiol level for the initiation of micronized progesterone to optimize outcomes in NPP cycles potentially restricting scheduling flexibility? Summary answer All follicular sizes &amp;gt;12 mm and estradiol levels &amp;gt;120 pg./mL do not significantly correlate with ongoing pregnancy rates (OPR) or pregnancy loss (PL). What is known already Planning of a frozen embryo transfer (FET) is feasible within either a natural (NC) or artificial cycle (AC). While AC-FETs offer flexibility in planning, concerns have raised due to studies indicating a higher risk for obstetric complications. Conversely, NC-FETs show a protective effect against these complications but are usually less flexible in planning and ask for more monitoring. Recently, the natural proliferative phase (NPP) protocol was described, in which luteal phase support is initiated as soon as the endometrium reaches 7mm. NPP-FETs were associated with ongoing pregnancy rates comparable to AC- and NC-FETs. Study design, size, duration A retrospective single-centre study including a total of 300 consecutive single frozen embryo transfers (FET), performed at a tertiary fertility centre between March 2023 and December 2023. All cycles were single blastocyst transfer cycles retained from IVF/ICSI cycles with autologous oocytes. Participants/materials, setting, methods A total of 227 patients underwent one or more frozen embryo transfer cycles. Administration of MVP 800mg BID was initiated after fulfilling the following criteria: follicular size &amp;gt; 12mm, estradiol level ≥120ng/mL and endometrium thickness ≥7mm. Blastocyst transfers were scheduled on the fifth day of MVP administration. Serum progesterone (P4) levels were determined on the day of transfer. Associations between treatment outcome, patient and cycle characteristics were explored using generalized estimating equations analyses. Main results and the role of chance The follicular size and estradiol level on the day of MVP initiation was not significantly associated with pregnancy rate (PR), ongoing pregnancy rate (OPR) or pregnancy loss (PL) (p = 0.386 and p = 0.260; p = 0.830 and p = 0.467; p = 0.978 and p = 0.313 respectively). Mean number of visits needed prior to the initiation of the MVP for scheduling the embryo transfer was 2.4 (SD 1.3). PR, but not OPR, was significantly associated with both the duration of the follicular phase as well as the number of visits (p = 0.008 and p = 0.006 respectively). For 91.3 % (274/300) of patients, embryo transfer could be scheduled on a weekday. 49% (146/300) of patients had a positive hCG test after the fresh blastocyst transfer in the NPP cycle. Ongoing pregnancy rate was 35 % (104/300), whereas pregnancy loss (early clinical miscarriage and biochemical pregnancy) was 23% (33/146). The OPR was significantly related to the age of the patient (p = 0.029). Both the PR as the OPR were significantly related the blastocyst quality (p = 0.008 and 0.009 respectively). The incidence of pregnancy loss was only significantly associated with blastocyst quality (p = 0.027). Mean serum P4 level at day of transfer was 19.4 ng/ml (SD 6.1) with a P4 level above 10ng/ml in 97% of cycles. Limitations, reasons for caution The retrospective character is a limitation of this study as well as the absence of live birth rate as a clinical outcome variable. Wider implications of the findings Flexibility about the required follicular sizes and estradiol levels open the perspective for exploring more flexible planning criteria such as lower thresholds for endometrial thickness. Further studies are needed to investigate whether ovulation occurs with formation of functional corpora lutea to effectively protect against hypertensive disorders. Trial registration number ONZ-2024-0015

O-303 What is the ideal dose of daily FSH after corifollitropin-alfa? A multicentre-randomized control trial

Abstract Study question Does the mean serum trigger-progesterone levels show significant variation based on the administered rFSH dose from day 8 onwards during ovarian stimulation using corifollitropin-alfa? Summary answer Lower rFSH doses from day 8 of ovarian stimulation onwards are linked to reduced serum progesterone (P4) levels without impact on cumulus-oocyte complexes. What is known already Progesterone elevation during ovulation trigger prompts a non-elective freeze-all strategy, given the lower live birth rates in fresh embryo transfers. Ongoing research explores methods to mitigate late follicular phase P4 rise to allow a fresh embryo transfer. Granulosa cells’ progesterone production is an FSH-driven and dose-dependent process, and FSH dose is furthermore pivotal for a good ovarian response. Balancing FSH dose is crucial for both optimal ovarian response and preventing undesirable P4 elevation while maintaining an adequate number of retrieved oocytes and allowing a fresh embryo transfer. Study design, size, duration This study is an interim-analysis of a randomized-controlled multi-center clinical-trial comparing three ovarian-stimulation-protocols: (A) corifollitropin alfa (CFA) followed by rFSH 50 IU/day; (B) CFA followed by rFSH 150 IU/day; (C) CFA followed by rFSH 250 IU/day.The primary outcome is the serum-progesterone-level on the day of hCG among the study groups, secondary outcomes included number of oocytes, clinical pregnancy rates and freeze-all cycles. 167 women (of 261) were randomized between July 2019-November 2023, with a 1:1allocation. Participants/materials, setting, methods Young (&amp;lt;40 years old), normo-ovulatory cycle (25-35 days), with AFC&amp;gt;7 and &amp;lt;20, and a BMI&amp;lt;29 Kg/m2 patients were recruited in the fertility clinic of three different tertiary university hospitals. On day 8 of ovarian stimulation (OS) following CFA administration, patients who needed additional rFSH were randomized into 3 groups (A-B-C). The OS was performed in a GnRH-antagonist protocol and the ovulation triggered with hCG. A fresh embryo-transfer was performed on day 5 following oocyte retrieval. Main results and the role of chance Overall, 167 patients were randomized, 60 in group A, 55 in group B and 52 in group C. The mean age and BMI were comparable between the groups. Mean AMH was respectively 2.2, 2.1 and 2.2 ng/mL, for group A, B and C (p = 0.95). Group A resulted in a significantly lower P4 level at trigger as compared with group B and C (respectively, 0.4ng/mL, 0.9 ng/mL and 1.4 ng/mL; p &amp;lt; 0.001). The mean number of retrieved oocytes was 10.7, 11 and 12.1 for group A, B and C, respectively (p = 0.47), while the mean number of mature oocytes was 7.3, 6.9 and 7.8 for group A, B and C, respectively (p = 0.7). A freeze-all approach was decided for 27%, 29% and 46% for group A, B and C respectively (p = 0.057). No significant differences were found for fresh-embryo-transfer outcomes (chemical pregnancy rates: 33%, 31% and 29%, respectively for A, B and C (p = 0.12).Of interest, comparisons between serum FSH at trigger showed a mean of 12.5, 17 and 20.5 IU/L for group A, B and C, respectively (p &amp;lt; 0.001) while the serum estradiol levels on day of trigger were comparable among the groups (1659, 2092 and 2098 ng/L for group A, B and C, respectively (p = 0.091). Limitations, reasons for caution This is an interim analysis planned to detect the mean difference in COC between groups. Therefore, the mean differences of the primary outcome should be interpreted as exploratory findings which warrant future investigation. Wider implications of the findings Administering a lower rFSH dose from day 8 onward during ovarian stimulation results in comparable numbers of COC but also leads to significantly lower serum P4 levels. Consequently, this finding has the potential to reduce the overall consumption of rFSH, thereby possibly increasing the likelihood of a fresh embryo transfer. Trial registration number NCT03686852