IVF-conceived Pregnancies Research Articles

Association of in vitro fertilization with severe maternal morbidity in low-risk patients without comorbidities

To determine whether an association exists between invitro fertilization (IVF) and severe maternal morbidity among low-risk pregnant patients. Retrospective cohort study. Low-risk pregnant patients who delivered between January 2019 and December 2022. Low-risk was defined as having an obstetric comorbidity index score of 0. Invitro fertilization. The primary outcome (dependent variable) was any severe maternal morbidity. The secondary outcome was the need for a cesarean delivery. A modified Poisson regression with robust error variance was used to model the probability of severe maternal morbidity as a function of IVF. Risk ratios and their associated 95% confidence intervals (CIs) were computed. An α value of 0.05 was considered statistically significant. A total of 39,668 pregnancies were included for analysis, and 454 (1.1%) were conceived by IVF. The overall severe maternal morbidity rate was 2.4% (n = 949), with the most common indicator being blood transfusion. The overall cesarean delivery rate was 18.8% (n = 7,459). On modified Poisson regression, IVF-conceived pregnancies were associated with 2.56 times the risk of severe maternal morbidity (95% CI, 1.73-3.79) and 1.54 times the risk of having a cesarean delivery (95% CI, 1.37-1.74) compared with non-IVF pregnancies. Invitro fertilization is associated with higher rates of severe maternal morbidity, primarily the need for a blood transfusion, and cesarean delivery in low-risk pregnancies without major comorbidities. Recognizing this association allows healthcare providers to implement proactive measures for better monitoring and tailored postpartum care.

Neonatal outcomes from in vitro fertilization-conceived pregnancies

Background In vitro fertilization (IVF) shows potential to improve pregnancy success, especially for infertile couples. This technique has some risks for neonates in the perinatal period and may affect their future health.
 Objective To investigate the characteristics and clinical outcomes of neonates from IVF-conceived pregnancies.
 Methods This retrospective study was conducted in neonates from IVF-conceived pregnancies from January to December 2021 at Bunda Women’s and Children’s Hospital, Jakarta. We gathered data from medical records about maternal age and morbidity, gravidity, gestational age, method of delivery, multiple gestation, also neonates’ significant profiles like prematurity, birth weight, Apgar score, and morbidities in perinatal period. We would like to investigate the characteristics and clinical outcomes of neonates born from IVF-conceived pregnancies program.
 Results There were 361 neonates whose mothers underwent IVF included in this study. Most mothers were ?35 years (70.9%) and on their first pregnancy (69.2%). Maternal complicating factors were premature contractions (16.6%), premature rupture of membranes (8.3%), and twin pregnancy (31.5%). About 98.6% of deliveries were performed by caesarean section and from IVF-conceived pregnancies program most 61.2% neonates were born at full term gestation (61.2%). Preterm deliveries occurred at a mean gestational age of 34.4 (SD 2.4) weeks. Subjects’ mean birth weight was 2,800.2 (SD 640.3) grams, with 26.3% in the low-birth-weight category. Most neonates (93.0%) were appropriate weight for gestational age and had good Apgar scores in the first minute (92.2%) and fifth minute (99.7%). However, 24.3% of neonates needed intensive care (NICU) with morbidities. The longest length of NICU stay was 100 days, with mortality of 7.9% of NICU-treated infants.
 Conclusion In our setting, most neonates from the IVF program were born with good outcomes, although preterm birth rate, low birth weight, need for NICU care, and mortality rate were quite high. Further study is needed to evaluate long-term outcomes of IVF neonates.

Preconception Vitamin D Level and In Vitro Fertilization: Pregnancy Outcome

Vitamin D deficiency impairs female fertility and the success of in vitro fertilization (IVF). The recommended serum 25-hydroxy vitamin D (25(OH)D) level in IVF-conceived pregnancies is still debated. We aimed to explore the relationship of preconception serum 25(OH)D level with pregnancy outcome following IVF treatment. We also explored the utility of the currently recommended serum 25(OH)D cut-off of ≥50 nmol/L for women undergoing IVF therapy. Retrospective cohort of women who had undergone IVF therapy. Of the women who started IVF therapy (n=354), 218 completed the study. This comprised two groups, successful pregnancy (pregnant group, n=160) and those who did not achieve a successful pregnancy (non-pregnant group, n=58). Preconception serum samples were analyzed for reproductive hormones, fasting glucose, insulin and 25(OH)D levels. Overall, median (IQR) age was 32(6) years, BMI 25.7(7.4) kg/m2 and HbA1c 5.2(0.6)%. 25(OH)D level was significantly higher at preconception in the pregnant group (56.4(21.4) vs 47.9(29.16) for non-pregnant; p=0.001). Preconception 25(OH)D level was a significant predictor of IVF outcome (B=0.04; 95% CI: 1.01, 1.06; p=0.001), with greater IVF success associated with a serum 25(OH)D level ≥50 nmol/L (OR: 0.46; p=0.01). Preconception 25(OH)D sufficiency (≥50 nmol/L) associates with successful pregnancy outcome following IVF therapy.

Early Predictors of Gestational Diabetes Mellitus in IVF-Conceived Pregnancies

Gestational diabetes mellitus (GDM) is associated with adverse maternal and fetal outcomes. This study aimed to identify early and reliable GDM predictors that would enable implementation of preventive and management measures. The participants were a 28-week prospective cohort of invitro fertilization (IVF)-conceived pregnant women (≤39 years, body mass index [BMI] 18.5-38 kg/m2) without a known history of diabetes mellitus. Fasting blood samples were analyzed at baseline (pre-IVF) and 12 weeks' gestation for reproductive hormones, glucose, serum insulin, lipids, thyroid function, adiponectin, and lipopolysaccharide-binding protein. At 28 weeks, a 75-g oral glucose tolerance test was used to screen for GDM. For the overall group at baseline, 22% had BMI ≥30 kg/m2, 45% had polycystic ovary syndrome, 16% had hemoglobin A1C of 5.7% to 6.1%, and 14% had a past history of GDM. At 28 weeks of gestation (n= 158), 34 women had developed GDM and 124 had not. Significant baseline predictors of GDM onset included greater BMI (29.0 vs 25.8 kg/m2), older age (34 vs 32 years), higher levels of follicle-stimulating hormone/luteinizing hormone ratio (1.2 vs 1.0), hemoglobin A1C (5.5 vs 5.2%), insulin (10.6 vs 7.1 μIU/mL), homeostatic model assessment of insulin resistance (2.2 vs 1.7), total cholesterol (199 vs 171 mg/dL), and low-density lipoprotein cholesterol (123 vs 105 mg/dL), and lower triglyceride levels (74 vs 76 mg/dL). Significant 12-week GDM predictors included greater maternal weight gain (delta: 3.4 vs 1.5 kg) and higher levels of insulin (11.3 vs 7.6 μIU/mL), triglycerides (178 vs 120 mg/dL), and homeostatic model assessment of insulin resistance (2.3 vs 1.5). Twelve-week BMI is a predictor of GDM following adjustment for polycystic ovary syndrome status and maternal age. While preconception maternal BMI, age, and follicle-stimulating hormone/luteinizing hormone ratio are predictors of subsequent development of GDM, early IVF-conceived gestational weight gain is the best predictor of GDM onset.

The importance of ultrasound preceding cell-free DNA screening for fetal chromosomal abnormalities.

This study aims to determine the incidence of ultrasound findings that may change clinical management on the day of blood-sampling for cell-free DNA (cfDNA) screening. A retrospective study was conducted at a tertiary provider of obstetric and gynecological ultrasound in Melbourne, Australia. Individual patient files were reviewed and results were collated for maternal characteristics, pre-cfDNA ultrasound reports, results and test characteristics of both cfDNA and diagnostic testing, and genetic counselling notes. The primary outcome was a potential change in patient management due to findings detected on the pre-cfDNA ultrasound. Of 6250 pre-cfDNA ultrasounds, 6207 were included in analysis. Of these, 598 (9.6%) pregnancies had a finding on pre-cfDNA ultrasound that had the potential to change management. The reasons for this potential change in management were detection of gestational age below 10 weeks (245, 3.9%), miscarriage (175, 2.8%), demised twin (43, 0.7%), fetal edema (115, 1.9%) and major structural abnormalities (20, 0.3%). These findings were more common in patients of advanced maternal age and in spontaneous conceptions. An ultrasound prior to cfDNA screening has the potential to change clinical management in almost one in 10 women. The proportion is higher in older age groups and lower in IVF-conceived pregnancies.

Effects of in vitro fertilization (IVF) therapies on metabolic, endocrine and inflammatory status in IVF-conceived pregnancy.

In vitro fertilization (IVF) is a common treatment for infertility. In mice, IVF is associated with development of glucose intolerance. However, human data are limited regarding the metabolic, endocrine and inflammatory effects of IVF therapy in IVF-conceived pregnancies. To explore effects of IVF therapies on metabolic, endocrine and inflammatory parameters in IVF-conceived pregnancy. Twelve-week prospective observational study of adult normoglycaemic women, BMI 18.5-38kg/m2 and ≤39years awaiting IVF therapy. Fasting blood samples were collected at baseline and 12weeks, and serum analysed for reproductive hormones, glucose, lipids, insulin sensitivity, thyroid status, adiponectin inflammatory marker and lipopolysaccharide-binding protein (LBP). Two hundred and seventy-five women were analysed: 158 IVF-conceived pregnant women and 117 with failed IVF. Compared with baseline, nonpregnant women had significant (P<.001) increases in 12-week glucose (86.04-87.62mg/dL), insulin (8.72-9.37µIU/mL), HOMA-IR (1.9-2.1), T-Chol (169.5-174.9mg/dL), TG (71.0-83.7mg/dL) and HDL-C (52.0-54.11mg/dL) levels. At 12weeks, pregnant women also had (P<.001) increases in T-Chol (177.5-199.5mg/dL), TG (73.5-126.78mg/dL) and HDL-C (55.3-65.1mg/dL), while a significant reduction in glucose (86.15-82.19mg/dL), HbA1c (5.3-5.08%) and TSH (1.71-1.36µIU/mL) levels from baseline. Adiponectin and LBP levels remained the same in either group. In vitro fertilization hormonal therapy impairs glucose and insulin levels; these effects are masked in early pregnancy. Changes in lipid profile occur following IVF therapies regardless of pregnancy outcome. Neither adiponectin nor LBP is affected by IVF therapies and during early IVF-conceived pregnancy.

The incidence of hypertensive disorders of pregnancy following sperm donation in IVF: an Australian state-wide retrospective cohort study.

Does IVF using donor sperm increase the risk of hypertensive disorders of pregnancy and fetal growth restriction (FGR)? IVF conceptions arising from sperm donation are not associated with an increased risk of hypertensive disorders of pregnancy or FGR. It has been hypothesized that the absence of prior exposure to factors within the paternal ejaculate increases the risk of preeclampsia and FGR among nulliparous women or women with a new partner-the concept of 'primipaternity'. It remains unclear which element of the ejaculate is responsible: the sperm cell or the constituents of seminal fluid. IVF pregnancies arising from donor sperm where the seminal fluid is absent provide a unique opportunity to test the theory of primipaternity and the relative contribution of the sperm cell. Pregnancies conceived via artificial reproductive technology are at increased risk of preeclampsia and FGR. Theories about the development of preeclampsia and the relative contribution of spermatic factors were explored by comparing the risk of hypertensive disorders of pregnancy and FGR among IVF pregnancies conceived with autologous gametes (own eggs and partner sperm) and those conceived with donor sperm, donor egg (and partner sperm) and donor embryo. To do this, we performed a retrospective cohort analysis of pregnancy outcomes among singleton pregnancies (n= 15 443) conceived through fertility clinics within Australia between 2009 and 2017. All pregnancies resulting in a singleton pregnancy delivering after 20weeks' gestation were included. The cohort was divided into donor sperm, donor egg and donor embryo (where both gametes came from a donor to create an embryo, or in a surrogate pregnancy) groups. We also compared the data with a control group, defined as IVF-conceived pregnancies from autologous cycles. A multivariable regression model was used to calculate an adjusted odds ratio (aOR). The final cohort contained 1435, 578 and 239 pregnancies conceived by donor sperm, donor egg and donor embryo, respectively, and 13 191 controls. There were a very small number of women lost to follow-up (31 women; 0.2% of total cohort). Compared to control pregnancies, there was no increase in the risk of hypertensive disorders among pregnancies conceived via donor sperm (aOR 0.94; 95% CI 0.73-1.21). Subgroup analysis was performed for a cohort where parity was known (n= 4551), and of these, 305 multigravida pregnancies were conceived via donor sperm. Among this cohort, no increased risk of preeclampsia or pregnancy-induced hypertension was found (aOR 1.18; 95% CI: 0.69-2.04) as a result of primipaternity (new sperm donor).A significantly increased risk for hypertensive disorders of pregnancy was associated with the use of donor eggs (but partner sperm; aOR 2.34; 95% CI 1.69-3.21). However, the association was no greater among pregnancies conceived with donor embryos (i.e. donated egg and sperm; aOR 2.0; 95% CI 1.25-3.17) than among the donor oocyte group. The overall incidence of FGR (defined as birthweight <10th centile) was 18%. There were no significant differences observed between donor sperm, or donor embryo pregnancies; however, egg donation was associated with a 1.5-fold increase in FGR. This study was limited by a lower than expected rate of hypertensive disorders of pregnancy (n= 862, 5.6%), which is contrary to the well-established increased risk among women using IVF. However, this is likely to be evenly distributed across the study groups and, therefore, unlikely to have introduced significant bias. These findings suggest that exposure to new sperm may not be implicated in the pathogenesis of preeclampsia. The mechanism of increased risk seen in conceptions arising from egg or embryo donation remains unclear. Further investigation is required to elucidate these mechanisms and, ultimately, improve pregnancy outcomes following IVF. This study was supported by the Australian Commonwealth Government-Graduate Research Scheme (A.K.). Salary support was provided by the National Health and Medical Research Council of Australia (S.T.), Mercy Foundation (A.L.), and the Department of Obstetrics and Gynaecology at the University of Melbourne (R.H.). There are no competing interests.

Risk of severe maternal morbidity associated with in vitro fertilisation: a population‐based study

To investigate the association between invitro fertilisation IVF and severe maternal morbidity (SMM) and to explore the role of multiple pregnancy as an intermediate factor. Population-based cohort-nested case-control study. Six French regions in 2012/13. Cases were 2540 women with SMM according to the EPIMOMS definition; controls were 3651 randomly selected women who gave birth without SMM. Analysis of the associations between IVF and SMM with multivariable logistic regression models, differentiating IVF with autologous oocytes (IVF-AO) from IVF with oocyte donation (IVF-OD). The contribution of multiple pregnancy as an intermediate factor was assessed by path analysis. Severe maternal morbidity overall and SMM according to its main underlying causal condition and by severity (near misses). The risk of SMM was significantly higher in women with IVF (adjusted OR=2.5, 95% CI 1.8-3.3). The risk of SMM was significantly higher with IVF-AO, for all-cause SMM (aOR=2.0, 95% CI 1.5-2.7), for near misses (aOR=1.9, 95% CI 1.3-2.8), and for intra/postpartum haemorrhages (aOR=2.3, 95% CI 1.6-3.2). The risk of SMM was significantly higher with IVF-OD, for all-cause SMM (aOR=18.6, 95% CI 4.4-78.5), for near misses (aOR=18.1, 95% CI 4.0-82.3), for SMM due to hypertensive disorders (aOR=16.7, 95% CI 3.3-85.4) and due to intra/postpartum haemorrhages (aOR=18.0, 95% CI 4.2-77.8). Path-analysis estimated that 21.6% (95% CI 10.1-33.0) of the risk associated with IVF-OD was mediated by multiple pregnancy, and 49.6% (95% CI 24.0-75.1) of the SMM risk associated with IVF-AO. The risk of SMM is higher in IVF pregnancies after adjustment for confounders. Exploratory results suggest higher risks among women with IVF-OD; however, confidence intervals were wide, so this finding needs to be confirmed. A large part of the association between IVF-AO and SMM appears to be mediated by multiple pregnancy. The risk of severe maternal morbidity is higher in IVF-conceived pregnancies than in pregnancies conceived by other means.

Risk of spontaneous preterm birth in IVF-conceived twin pregnancies

Objective: To compare the mean transvaginal ultrasound (TVU) cervical length (CL) at midtrimester in screening for preterm birth in in vitro (IVF)-conceived twin pregnancies versus spontaneously-conceived twin pregnancies. Methods: This was a retrospective cohort study. Potential study subjects were identified at the time of a routine second trimester fetal ultrasound exam at 18 0/7 to 23 6/7-week gestation. All women with twin diamniotic pregnancies screened with a single TVU CL for this trial were included. Mean TVU CLs were compared between IVF-conceived twin pregnancies and spontaneously-conceived twin pregnancies. The relationship of TVU CL with gestational age at delivery was assessed. Incidence of short TVU CL, defined as TVU CL ≤30 mm, was also calculated in the two groups. The primary outcome was the mean of TVU CL. Distribution of CL was determined and normality was examined in both groups Results: A total of 668 women with diamniotic twin pregnancies who underwent TVU CL screening between 18 0/6 and 23 6/7 weeks were included. 158 (23.7%) were IVF-conceived pregnancies, and 510 (76.3%) were spontaneously-conceived pregnancies. No women received progesterone, pessary, or cerclage for preterm birth prevention during pregnancy. The mean TVU CL was significantly lower in the IVF-conceived group (32.2 ± 10.5 mm) compared to the spontaneously-conceived group (34.1 ± 9.1 mm) (mean difference (MD) − 1.90 mm, 95%CI −3.72 to −0.08). The incidence of TVU CL ≤30 mm was 30.4% in the IVF-conceived group and 21.6% in the spontaneously-conceived group (adjusted odds ratio (aOR) 1.59, 95%CI 1.06–2.37). IVF-conceived twins had a significantly higher risk of spontaneous preterm birth <34 weeks (32.9 versus 21.2%; aOR 1.83, 95% confidence interval (CI) 1.23–2.71) and higher rate of delivery due to spontaneous onset of labor (64.5 versus 54.9%; aOR 1.50, 95%CI 1.03–2.17). For any given TVU CL measured between 18 0–7 and 23 6/7 weeks, gestational age at delivery for IVF-conceived twins was earlier by about 1 week on average compared with spontaneously-conceived twins. Conclusions: The higher rate of spontaneous preterm birth in IVF-conceived twin pregnancies is predicted by lower midtrimester TVU CL, as well as by the lower gestational age at birth per any given CL in the IVF-conceived compared to the spontaneously-conceived twin pregnancies.

Angiogenic profiles in in-vitro fertilization/embryo transfer (IVF/ET) treatments: relationship to hypertensive complications in IVF-conceived pregnancies

Angiogenic profiles in in-vitro fertilization/embryo transfer (IVF/ET) treatments: relationship to hypertensive complications in IVF-conceived pregnancies

Risks of spontaneously and IVF-conceived singleton and twin pregnancies differ, requiring reassessment of statistical premises favoring elective single embryo transfer (eSET).

A published review of the literature by Dutch investigators in 2004 suggested significant outcome differences between spontaneously - and in vitro fertilization (IVF) - conceived singleton and twin pregnancies. Here we review whether later studies between 2004–2015 confirmed these findings. Though methodologies of here reviewed studies varied, and all were retrospective, they overall confirmed results of the 2004 review, and supported significant outcome variances between spontaneously- and IVF-conceived pregnancies: IVF singletons demonstrate significantly poorer and IVF twins significantly better perinatal outcomes than spontaneously conceived singletons and twins, with differences stable over time, and with overall obstetrical outcomes significantly improved. Exaggerations of severe IVF twin risks are likely in the 50 % range, while exaggerations of milder perinatal risks are approximately in 25 % range. Though elective single embryo transfers (eSET) have been confirmed to reduce pregnancy chances, they are, nevertheless, increasingly utilized. eSET, equally unquestionably, however, reduces twin pregnancies. Because twin pregnancies have been alleged to increase outcome risks in comparison to singleton pregnancies, here reported findings should affect the ongoing discussion whether increased twin risks are factual. With no risk excess, eSET significantly reduces IVF pregnancy chances without compensatory benefits and, therefore, is not advisable in IVF, unless patients do not wish to conceive twins or have medical contraindications to conceiving twins.

The association of crown-rump length discrepancy with birthweight discordance in spontaneous versus assisted conception dichorionic twins

This study aimed to compare the associations of crown-rump length (CRL) discrepancy with birthweight discordance in spontaneous versus vitro fertilization (IVF) conceived dichorionic twin pregnancies. A computerized retrospective study of women referred to our ultrasonographic unit for nuchal translucency examination between January 1997 and December 2011. The study group was subdivided into twins conceived after IVF, non-IVF fertility treatment and spontaneously conceived twins. Birthweight discordance was defined as a difference of birthweights of >20%. A total of 688 dichorionic twin pregnancies were included, all of them ending in live birth of both twins. IVF-conceived pregnancies were associated with a significant increased risk of extreme birthweight discordance compared with spontaneous-conceived twin pregnancies (OR = 2.3; CI = 1.4-3.8, P < 0.001). A significant correlation was found between CRL discrepancy and birthweight discordance in spontaneous-conceived pregnancies (r = 0.15, P < 0.05). In contrast, there was no significant correlation between CRL discrepancy and birthweight discordance in both IVF and fertility treatment-conceived pregnancies. Because birthweight discordance in IVF-conceived twins did not correlate with CRL discrepancy, we assume that it emerges later in pregnancy, maybe related to maternal underplaying complications, for which IVF was indicated in the first place.

Socioeconomic status affects the prevalence, but not the perinatal outcomes, of in vitro fertilization pregnancies.

Does maternal socioeconomic status (SES) confound or modify the association between IVF and perinatal outcome among singleton births? There were substantial socioeconomic differences in the frequency of IVF pregnancies, but maternal SES was not associated with the outcome of IVF pregnancies. The use of IVF is associated with SES. Additionally, women with lower SES tend to have an increased risk of adverse perinatal outcomes such as preterm birth and small for gestational age birth. We conducted a population-based cohort study using the Finnish Medical Birth Register (2006-2010). We analyzed the total population of singleton births in Finland (n = 291 004) and then compared the unadjusted and adjusted incidences of adverse perinatal outcomes for singleton births after IVF (n = 5647) and non-IVF pregnancies (n = 285 357) in relation to SES. SES did not confound or modify the association between IVF and perinatal outcomes after adjustments for age, parity, smoking, gestational diabetes, maternal diabetes and pre-eclampsia. However, the prevalence of IVF pregnancies increased with SES; on average 1.9% of singleton infants were born after IVF pregnancies, while the corresponding percentages were 3.2 and 1.2% for the highest and lowest SES strata, respectively. IVF was statistically significantly associated with 1.27-, 1.49-, 1.63-, 1.47-, 1.35-, 1.40-, 4.97- and 1.14-fold higher incidences of admission to a neonatal unit, stillbirth, preterm birth, low birthweight, low Apgar scores (<7 at 5 min), Cesarean section, placenta previa and major congenital anomaly, respectively. Irrespective of the SES group, women who became pregnant through IVF were older and more often nulliparous and non-smokers compared with women with non-IVF pregnancies. The occupation of 22% of the women was unknown and that of a further 25% did not match any of the criteria for our SES strata. Additionally, infertility is a problem for couples but the definition of SES in this study was based only on the mother's occupation at the time of birth. The prevalence of IVF-conceived pregnancies was highest among the highest SES group, but SES did not confound the perinatal outcomes of IVF pregnancies after adjusting for background factors. However, the magnitude of risks associated with the IVF technique itself may be more significant than previously thought. None of the authors received any funding specifically for this study, and we have no competing interests.

Controlled Ovarian Hyper‐stimulation during IVF treatment does not increase the risk of preterm delivery compared to the transfer of frozen–thawed embryos in a natural cycle

Preterm delivery rates are significantly higher for IVF-conceived pregnancies compared with naturally conceived pregnancies, even following adjustment for relevant confounding factors. Furthermore, preterm delivery is reportedly more common in pregnancies from fresh embryo, rather than frozen-thawed embryo transfer (FET), suggesting that the controlled ovarian hyperstimulation (COH) environment may initiate preterm labour. As prior studies have confirmed a positive correlation between the numbers of corpora lutea generated during COH and serum relaxin levels, a reported trigger for cervical remodelling and preterm labour, the aim of this study was to examine the hypothesis that preterm delivery rates will therefore be lower in mono-follicular FET cycles compared to multi-follicular COH/IVF cycles (primary hypothesis). Our secondary hypothesis was that COH/IVF cycles yielding higher numbers of oocytes will be associated with higher rates of preterm birth and subsequent lower birth weight than those producing lower numbers of oocytes. Retrospective review of 702 singleton pregnancies resulting from IVF treatment (COH/IVF and FET) during the years 2008-2009 at a single private IVF centre in Adelaide, South Australia. There was no significant difference in rates of preterm labour between women undergoing COH with fresh embryo transfers compared with frozen embryo transfers (FETs), (11.59 vs 10%, P=0.6011), nor was there any difference in the median gestation at delivery (39.4 vs 39.1weeks, respectively, P=0.1538). The rate of preterm delivery in both the fresh and frozen embryo transfer cohorts was higher than that observed in the general obstetric population (6.76%). A weak but marginally statistically significant correlation was observed between the number of oocytes retrieved following COH and gestation at delivery (r=0.089, P=0.048). While a woman's response to COH was weakly negatively correlated with gestation at delivery, this relationship was not of major clinical importance as the rate of preterm delivery and the median gestation at delivery were not significantly different between pregnancies resulting from fresh or FETs in our study cohort.