Gonadotropin-releasing Hormone Antagonist Groups Research Articles

Outcomes and cost-effectiveness comparisons of progestin-primed ovarian stimulation, GnRH antagonist protocol, and luteal phase stimulation for fertility preservation.

To compare the clinical outcomes and cost-effectiveness of progestin-primed ovarian stimulation (PPOS) and the gonadotropin-releasing hormone-antagonist (GnRH-A) protocol in fertility preservation (FP) in cancer patients. The stimulation option when patients were in the luteal phase was also explored. This retrospective study analyzed clinical data from 163 patients who underwent FP. The number of retrieved oocytes and vitrified oocytes/embryos, total dose of gonadotropin, duration of stimulation, number of injections, and cost were compared among the PPOS, GnRH-A, and luteal phase stimulation (LPS) groups. No significant differences were noted in the numbers of retrieved oocytes and vitrified oocytes/embryos among the three groups. In the multiple regression model, age (P = 0.02) and antral follicle count (AFC) (P < 0.001), but not the controlled ovarian stimulation (COS) protocols (P = 0.586), were associated with the number of retrieved oocytes. The number of injections and the cost were all significantly lower in the PPOS and LPS groups than in the GnRH-A group(P < 0.001). PPOS had similar clinical results but was superior medically and economically to GnRH-A. For patients in the luteal phase, LPS was an optional protocol with similar outcomes and costs to PPOS.

Oral Gonadotropin-Releasing Hormone Antagonist Relugolix Has the Same Effect as Gonadotropin-Releasing Hormone Agonist Injections in Terms of Preparation for Transcervical Resection Myomectomy.

For preparing the optimal condition in transcervical resection (TCR) surgery, gonadotropin-releasing hormone (GnRH) agonist has been utilized. Recently, an oral GnRH antagonist (relugolix) is available and acts directly on GnRH receptor, avoiding flare up and reducing blood E2 levels rapidly. We retrospectively compared the oral GnRH antagonist (n = 14) effect to that of subcutaneous GnRH agonist (n = 19) for the pretreatment of endometrium in TCR myomectomy. Endometrial thickening was determined by intraoperative videos. The color tone of the endometrium in the normal part was assessed by digital image processing. The median duration of the first GnRH agonist injection and the surgery was 67 days (21-136 days), which is significantly longer than that of the oral GnRH antagonist group, 18.5 days (7-157 days P < 0.01). Both the GnRH agonist and antagonist groups did not exhibit prominence in the endometrium. The GnRH antagonist group showed the same degree of whiteness in the normal endometrium as the GnRH agonist group. The oral GnRH antagonist administration could rapidly atrophy the endometrium and create an optimal surgical field for TCR in a short period.

Does the type of GnRH analogue used, affect live birth rates in women with endometriosis undergoing IVF/ICSI treatment, according to the rAFS stage?

Since the introduction of gonadotropin-releasing hormone (GnRH) antagonists, an extensive amount of literature investigating the role of the downregulation protocols on pregnancy outcomes has been published. However, these studies were mainly performed in the general infertile population where patients with endometriosis were often excluded or underrepresented. This study is a large retrospective cohort study including 386 endometriosis patients undergoing IVF/ICSI, who had been previously classified according to the rAFS system. Patients were stimulated either a long GnRH agonist or GnRH antagonist protocol. Depending on endometriosis stage, patients were divided into two groups: endometriosis stage I–II and endometriosis stage III–IV. Each group was subdivided, based on the type GnRH analog used. When comparing the GnRH agonist and antagonist groups, patients with endometriosis stage I–II, had a tendency toward higher β-hCG positive, clinical pregnancy, and live birth rates (42.8% vs. 26.7%; p = .07) in favor of GnRH agonist use. In endometriosis stage III–IV, no differences were observed between agonist and antagonist cycle in any of the pregnancy outcomes. Multivariate regression analysis did not reveal any significant predictor of live birth after adjusting for relevant confounders. Based on our findings, the chance to have a liveborn in endometriosis population seems not to be affected by the type of GnRH analog used, at least in advanced stages. Findings from stage I–II endometriosis cases merit consideration and further evaluation in a larger sample size is warranted.

Quality of life and psychosocial and physical well-being among 1,023 women during their first assisted reproductive technology treatment: secondary outcome to a randomized controlled trial comparing gonadotropin-releasing hormone (GnRH) antagonist and GnRH agonist protocols

To compare self-reported quality of life, psychosocial well-being, and physical well-being during assisted reproductive technology (ART) treatment in 1,023 women allocated to either a short GnRH antagonist or long GnRH agonist protocol. Secondary outcome of a prospective phase 4, open-label, randomized controlled trial. Four times during treatment a questionnaire on self-reported physical well-being was completed. Further, a questionnaire on self-reported quality of life and psychosocial well-being was completed at the day of hCG testing. Fertility clinics at university hospitals. Women referred for their first ART treatment were randomized in a 1:1 ratio and started standardized ART protocols. Gonadotropin-releasing hormone analogue; 528 women allocated to a short GnRH antagonist protocol and 495 women allocated to a long GnRH agonist protocol. Self-reported quality of life, psychosocial well-being, and physical well-being based on questionnaires developed for women receiving ART treatment. Baseline characteristics were similar, and response rates were 79.4% and 74.3% in the GnRH antagonist and GnRH agonist groups, respectively. Self-reported quality of life during ART treatment was rated similar and slightly below normal in both groups. However, women in the GnRH antagonist group felt less emotional (adjusted odds ratio [AOR] 0.69), less limited in their everyday life (AOR 0.74), experienced less unexpected crying (AOR 0.71), and rated quality of sleep better (AOR 1.55). Further, women receiving GnRH agonist treatment felt worse physically. Women in a short GnRH antagonist protocol rated psychosocial and physical well-being during first ART treatment better than did women in a long GnRH agonist protocol. However, the one item on self-reported general quality of life was rated similarly. NCT00756028.

Prevention of ovarian hyperstimulation syndrome in a rat model: comparison of the efficacy of tocilizumab with that of ranibizumab, cabergoline, and a gonadotropin-releasing hormone antagonist

The aim of the study is to investigate the effects of the interleukin-6 (IL-6) blocker tocilizumab in a hyperstimulated rat model and compare it with ranibizumab, a gonadotropin-releasing hormone antagonist (GnRHA), and cabergoline. Forty-seven rats were randomly divided into the following seven groups: Group 1: OHS; Group 2: OHS+ GnRHA; Group 3: OHS + ranibizumab; Group 4: OHS + cabergoline; Group 5: OHS + low-dose tocilizumab (TL); Group 6: OHS + high-dose tocilizumab (TH); Group 7: sham. Ovarian weight was significantly lower only in the ranibizumab group than in the OHS group. Estrogen levels were significantly lower in the GnRHA group than in the OHS and the treatment groups. Progesterone levels were significantly lower in the ranibizumab, cabergoline, and TL groups than in the OHS group. Among the treatment groups, corpus luteum counts were lower than in the OHS group. Corpus luteum counts were lowest in the tocilizumab groups. IL-6 intensity was lower in all treatment groups than in the OHS group. In the ranibizumab group IL-6 intensity was the lowest. The TL group did not significantly differ from the GnRHA and cabergoline groups regarding IL-6 expression. Ovarian VEGF expression was significantly lower in all treatment groups. For the TL, ranibizumab, and cabergoline groups VEGF intensity was similar. Tocilizumab may be a new strategy for preventing ovarian hyperstimulation syndrome by inhibition of IL-6.

Hypothalamic Suppression Decreases Bone Strength Before and After Puberty in a Rat Model

The incidence of menstrual irregularities, both primary and secondary amenorrhea, has been reported to be as high as 60%, with the highest incidence in younger athletes, suggesting possible adverse effects on bone development. It was hypothesized that in a rat model, suppressed hypothalamic activity via a gonadotropin-releasing hormone antagonist (GnRH-a) before onset of puberty would result in a relatively larger bone strength deficit compared with suppression after puberty. Hypothalamic suppression was achieved by providing GnRH injections. Animals received injections for 25 days either before puberty (pre group) (age 23-46 days) or after puberty (post group) (age 65-90 days). Body weights and uterine weights were measured. Serum estradiol was assayed. Mechanical strength of the right femora and histomorphometry of the left femur were measured. Suppression of the hypothalamic-pituitary-gonadal axis was confirmed by significant atrophy of uterine tissue and suppressed estradiol levels. The peak moment was significantly lower in the pre and post GnRH-a groups compared with control. The percentage difference of the average peak moment and stiffness values from the respective age-matched control groups yielded a greater percentage difference in the pre group. The cortical area was less in the GnRH-a-treated groups, but no significant difference between the relative deficits between pre and post groups were found. Hypothalamic-pituitary-gonadal axis suppression before puberty resulted in a significantly larger deficit in mechanical strength compared with postpubertal animals. The time before puberty may represent a time when skeletal strength is more compromised. Women experience both primary and secondary amenorrhea; however, the treatment may need to be different for each condition.

A comparison of gonadotropin-releasing hormone (GnRH) antagonist and GnRH agonist flare protocols for poor responders undergoing in vitro fertilization

To compare stimulation profiles, pregnancy, and live birth rates in poor responders during in vitro fertilization (IVF) cycles using either a gonadotropin-releasing hormone (GnRH) antagonist (cetrorelix) or a GnRH agonist flare protocol (leuprolide). Retrospective chart review. A university-affiliated IVF program. Women designated as poor responders based on a prior stimulation cycle or baseline follicle-stimulating hormone (FSH) level of >10 mIU/mL, who needed at least 375 IU of starting daily gonadotropins in the study cycle. Administration of GnRH agonist flare or GnRH antagonist protocol. Clinical pregnancy rate, live birth rate. For 68 GnRH antagonist and 45 GnRH agonist flare cycles, the groups were similar with respect to age (38.8 versus 38.6 years) and basal FSH concentration (8.33 versus 8.65 mIU/mL). No statistically significant differences between the protocol types were noted in peak estradiol levels, amount of gonadotropins used, number of oocytes obtained, or embryos transferred. The pregnancy rates (40% versus 45.2%) and live birth rates (27.7% versus 31.7%) in the GnRH antagonist and flare groups, respectively, were similar. We achieved excellent and comparable pregnancy and live birth rates in poor responders of advanced reproductive age with the use of either GnRH antagonist or flare protocol.

Comparisons of Different Dosages of Gonadotropin-Releasing Hormone (GnRH) Antagonist, Short-acting Form and Single, Half-dose, Long-acting Form of GnRH Agonist During Controlled Ovarian Hyperstimulation and in vitro Fertilization

Both gonadotropin-releasing hormone (GnRH) analogs and antagonists have been used for pituitary desensitization during controlled ovarian hyperstimulation (COH). We aimed to determine the minimum effective daily dose of GnRH antagonist in women undergoing COH. We also compared the efficiency of a GnRH antagonist and a GnRH agonist. Women undergoing in vitro fertilization/intracytoplasmic sperm injection and embryo transfer were divided into five groups: (1) cetrorelix 0.25 mg ( n = 86); (2) cetrorelix 0.2 mg ( n = 28); (3) cetrorelix 0.15 mg ( n = 30); (4) leuprolide acetate (LA) 0.5 mg/day ( n = 58); (5) single half-dose LA depot 1.88 mg ( n = 49). Cetrorelix was administered daily from menstrual day 8 until the day of human chorionic gonadotropin administration. LA or LA depot was started on day 21 of the previous menstrual cycle. We observed lower gonadotropin (Gn) dosages, estradiol (E2) levels and reduced risk of ovarian hyperstimulation syndrome (OHSS) in the GnRH antagonist groups. A higher risk of luteinizing hormone (LH) surge was noted in cetrorelix 0.2 and 0.15 mg groups. Gn dosages (IU)/E2 levels (pg/mL) in each group were: (1) 1,949.4/1,191.1; (2) 1,869.6/1,010.8; (3) 1,856.7/1,023.6; (4) 2,184.5/1,323.6; and (5) 2,103.5/1,313.5, respectively. LH/OHSS risks were: (1) 3.5%/5.8%; (2) 7.1%/3.6%; (3) 13.3%/3.3%; (4) 3.4%/8.6%; and (5) 2%/8.2%, respectively. Number of oocytes/embryos/grade I, II embryos were: (1) 9.4/7.9/5.8; (2) 7.5/4.2/3.6; (3) 6.3/4.1/3.1; (4) 12.3/8.9/6.6; and (5) 11.8/8.4/6.1, respectively. There was no significant difference in terms of clinical outcomes between groups 1, 4 and 5, except for higher abortion rates (AR) in group 1. Pregnancy rate (PR)/implantation rate (IR) ratios in groups 1, 4, and 5 were statistically higher than those in groups 2 and 3. Chemical PR/IR/AR were: (1) 30.2%/5.9%/7%; (2) 21.4%/5.1%/7.1%; (3) 16.7%/4.1%/10%; (4) 32.8%/5.5%/8.6%; and (5) 30.6%/5.7%/8.2%, respectively. The lowest effective dosage of cetrorelix for pituitary desensitization during COH luteolysis is 0.25 mg, resulting in a comparable PR but a higher AR when compared with GnRH agonist.

Comparisons of Different Dosages of Gonadotropin-Releasing Hormone (GnRH) Antagonist, Short-Acting form and Single, Half-Dose, Long-Acting form of GnRH Agonist during Controlled Ovarian Hyperstimulati

Objective: Both gonadotropin-releasing hormone (GnRH) analogs and antagonists have been used for pituitary desensitization during controlled ovarian hyperstimulation (COH). We aimed to determine the minimum effective daily dose of GnRH antagonist in women undergoing COH. We also compared the efficiency of a GnRH antagonist and a GnRH agonist. Materials and Methods: Women undergoing in vitro fertilization/intracytoplasmic sperm injection and embryo transfer were divided into five groups: (1) cetrorelix 0.25 mg (n=86); (2) cetrorelix 0.2 mg (n=28); (3) cetrorelix 0.15 mg (n=30); (4) leuprolide acetate (LA) 0.5 mg/day (n=58); (5) single half-dose LA depot 1.88mg (n=49). Cetrorelix was administered daily from menstrual day 8 until the day of human chorionic gonadotropin administration. LA or LA depot was started on day 21 of the previous menstrual cycle. Results: We observed lower gonadotropin (Gn) dosages, estradiol (E2) levels and reduced risk of ovarian hyperstimulation syndrome (OHSS) in the GnRH antagonist groups. A higher risk of luteinizing hormone (LH) surge was noted in cetrorelix 0.2 and 0.15mg groups. Gn dosages (IU)/E2 levels (pg/mL) in each group were: (1) 1,949.4/1,191.1; (2) 1,869.6/1,010.8; (3) 1,856.7/1,023.6; (4) 2,184.5/1,323.6; and (5) 2,103.5/1,313.5, respectively. LH/OHSS risks were: (1) 3.5%/5.8%; (2) 7.1%/3.6%; (3) 13.3%/3.3%; (4) 3.4%/8.6%; and (5) 2%/8.2%, respectively. Number of oocytes/embryos/grade Ⅰ, Ⅱ embryos were: (1) 9.4/7.9/5.8; (2) 7.5/4.2/3.6; (3) 6.3/4.1/3.1; (4) 12.3/8.9/6.6; and (5) 11.8/8.4/6.1, respectively. There was no significant difference in terms of clinical outcomes between groups 1, 4 and 5, except for higher abortion rates (AR) in group 1. Pregnancy rate (PR)/implantation rate (IR) ratios in groups 1, 4, and 5 were statistically higher than those in groups 2 and 3. Chemical PR/IR/AR were: (1) 30.2%/5.9%/7%; (2) 21.4%/5.1%/7.1%; (3) 16.7%/4.1%/10%; (4) 32.8%/5.5%/8.6%; and (5) 30.6%/5.7%/8.2%, respectively. Conclusion: The lowest effective dosage of cetrorelix for pituitary desensitization during COH luteolysis is 0.25 mg, resulting in a comparable PR but a higher AR when compared with GnRH agonist.

Delayed pubertal development by hypothalamic suppression causes an increase in periosteal modeling but a reduction in bone strength in growing female rats

The timing of the pubertal growth is a critical event in skeletal development. A delay in the onset of puberty has been correlated with increased stress fracture incidence in young women and as a result, suboptimal skeletal development may affect long-term bone strength. Gonadotropin releasing hormone antagonist (GnRH-a) injections were used to delay the onset of puberty in growing female rats. 23-day-old female rats were injected with a GnRH-antagonist at 2 dosage levels ( n = 15/group). The Low Dose group (1.25 mg/kg/dose) received daily injections for 27 days (sacrifice 49 days). The High Dose group received (5.0 mg/kg/dose) only 5 days per week over a 26 day period (sacrifice 48 days). Calcein injections measured bone formation activity on the periosteal and endocortical surfaces. Standard histomorphometric and biomechanical analyses were performed on the femora and ash content was measured on the tibiae of all animals. Serum estradiol and insulin-like growth factor (IGF)-1 levels were assayed. Significant delays in pubertal development occurred in the two GnRH-a groups as evidenced by delayed vaginal openings, decreased uterine and ovarian weights and suppressed estradiol levels compared to control. Femoral lengths were significantly shorter in the experimental groups and serum IGF-1 levels were higher than control. Bone strength and stiffness were significantly lower in the GnRH-a groups. Cortical bone area was decreased and total area was not different between groups. There was a significant decrease in % Ct.Ar/T.Ar. The decreased bone strength may have resulted from a decrease in the amount and distribution of bone, however, stress and Young's modulus were also decreased. There was a different response between endocortical formation indices and periosteal formation indices to the GnRH-a protocol. Endocortical bone formation rates decreased and there was an increase in periosteal labeled surface. A dose response between bone strength and GnRH-a dosage was found. The data suggest that hypothalamic suppression during pubertal development resulted in decreased bone strength which may result in fracture development.

Cryopreserved blastocyst transfer: impact of gonadotropin-releasing hormone agonist versus antagonist in the previous oocyte retrieval cycles

To assess any detrimental effect of gonadotropin-releasing hormone (GnRH) antagonists on oocyte quality and embryo development by comparing the outcome of cryopreserved-thawed blastocyst transfers for cycles using a GnRH agonist or GnRH antagonist protocol for the controlled ovarian stimulation in the oocyte retrieval cycle. Retrospective comparative study. Private IVF center. Seventy-seven women who underwent cryopreserved-thawed blastocyst transfer. The patients were divided into two groups based on whether they had been treated using a GnRH agonist long protocol (n = 44) or a GnRH antagonist multiple-dose protocol (n = 33) during the previous oocyte retrieval cycle. Cryopreserved-thawed blastocysts were transferred after endometrial preparation without pituitary suppression using a GnRH agonist. Implantation and clinical pregnancy rates. The postthaw survival rate and numbers of good quality blastocysts transferred were similar for the GnRH agonist and GnRH antagonist groups. Implantation and pregnancy rates for cryopreserved-thawed blastocyst transfer for the GnRH agonist group versus the GnRH antagonist group were 21.0% (25 of 119) versus 29.0% (27 of 93) and 38.6% (17 of 44) versus 51.5% (17 of 33), respectively, which was not statistically significantly different. No difference was found in terms of implantation and pregnancy rates when a GnRH agonist or GnRH antagonist was used in the previous oocyte retrieval cycle. Our results suggest that GnRH antagonists do not have a detrimental effect on oocyte quality or embryo development.

Effects of a gonadotropin-releasing hormone antagonist and altrenogest on luteinizing hormone concentration and ovulation in the mare

The objective of Experiment 1 was to determine a dose and frequency of gonadotropin-releasing hormone (GnRH) antagonist administration to effectively suppress serum luteinizing hormone (LH) concentration and to delay ovulation when administered to mares. The objectives of Experiment 2 were 1) to determine the effects of subcutaneous or intravenous administration of a GnRH antagonist or oral altrenogest on serum LH concentration in the estrual mare; and 2) to determine the effectiveness of human chorionic gonadotropin (hCG) in inducing ovulation in mares with suppressed LH concentrations. In Experiment 1, mares ( N = 20) were randomly assigned and treated with either 5% mannitol (control, single subcutaneous injection, 1 mL, at time 0; n = 5); low-dose GnRH antagonist (single subcutaneous injection, 0.01 mg/kg, at time 0; n = 5); frequent low-dose GnRH antagonist (subcutaneous injections, 0.01 mg/kg, at 0, 6, 18, and 24 hours; n = 5); or high-dose GnRH antagonist (single subcutaneous injection, 0.04 mg/kg, at time 0; n = 5). Both the frequent low-dose and high-dose GnRH antagonist treatments resulted in significantly lower LH concentrations compared with controls at 90, 102, and 114 hours after treatment ( P < .05). In Experiment 2, mares (N = 38) were randomly assigned and treated with subcutaneous sterile saline (control), altrenogest (oral), subcutaneous GnRH antagonist, or intravenous GnRH antagonist. LH concentration for the altrenogest group was lower than the control group at 3, 4, 18, and 30 hours after treatment ( P < .05). LH concentration for both the subcutaneous and intravenous GnRH antagonist groups were lower compared with the control group at several time points ( P < .05). Based on these data, dose but not frequency of administration of a GnRH antagonist lowered LH concentration in the estrous mare but did not delay ovulation. In addition, serum LH concentrations can be lowered and ovulation effectively postponed in mares treated with altrenogest followed by administration of hCG. This indicates that serum LH concentrations can be lowered and ovulation effectively postponed in mares treated with altrenogest followed by administration of hCG.

Gonadotropin‐Releasing Hormone Antagonist (Cetrorelix) Therapy Fails to Protect Nonhuman Primates (Macaca arctoides) From Radiation‐Induced Spermatogenic Failure

Treatment of men of reproductive age with radiation or alkylating agents often produces prolonged azoospermia. We previously demonstrated that suppression of testosterone (T) with gonadotropin-releasing hormone (GnRH) analogs restored spermatogenesis following atrophy induced by radiation or chemotherapy in rats. This study tested whether GnRH antagonist therapy could reverse radiation-induced testicular injury in primates with a similar protocol. Adult male stump-tailed macaques were given either 6.7 Gy radiation to the testis alone, 6.7 Gy radiation combined with GnRH-antagonist treatment starting on the day of exposure, or daily injections of the GnRH antagonist Cetrorelix for 3 months alone and were monitored for 18 months. Cetrorelix alone produced a 20-40-week fully reversible suppression of serum T, but although spermatogenic recovery was incomplete, 40%-90% of tubules contained differentiating germ cells. Following radiation alone, testis volumes were reduced to approximately 28% and sperm counts to less than 1% of pretreatment values. A biopsy at 18 months after radiation showed that only 3.0% of seminiferous tubule cross sections had germ cells. In irradiated animals that received GnRH antagonist, testis volumes were reduced to 18% of pretreatment volume, and at 18 months, only 1.9% of seminiferous tubule cross sections contained germ cells. Inhibin B values were reduced to 10% and 3% of pretreatment levels in the radiation-only and the radiation plus GnRH antagonist groups, respectively. Species differences exist in the testicular response to radiation, GnRH antagonist therapy, or both, so that rescue protocols that were successful in rodents might not work in primates.

Effects of a GnRH antagonist inhibition of luteinizing hormone during the preovulatory period in the mare

The objective of Experiment 1 was to determine a dose and frequency of gonadotropin-releasing hormone (GnRH) antagonist administration to effectively suppress serum luteinizing hormone (LH) concentration and to delay ovulation when administered to mares. The objectives of Experiment 2 were 1) to determine the effects of subcutaneous or intravenous administration of a GnRH antagonist or oral altrenogest on serum LH concentration in the estrual mare; and 2) to determine the effectiveness of human chorionic gonadotropin (hCG) in inducing ovulation in mares with suppressed LH concentrations. In Experiment 1, mares (N = 20) were randomly assigned and treated with either 5% mannitol (control, single subcutaneous injection, 1 mL, at time 0; n = 5); low-dose GnRH antagonist (single subcutaneous injection, 0.01 mg/kg, at time 0; n = 5); frequent low-dose GnRH antagonist (subcutaneous injections, 0.01 mg/kg, at 0, 6, 18, and 24 hours; n = 5); or high-dose GnRH antagonist (single subcutaneous injection, 0.04 mg/kg, at time 0; n = 5). Both the frequent low-dose and high-dose GnRH antagonist treatments resulted in significantly lower LH concentrations compared with controls at 90, 102, and 114 hours after treatment (P < .05). In Experiment 2, mares (N = 38) were randomly assigned and treated with subcutaneous sterile saline (control), altrenogest (oral), subcutaneous GnRH antagonist, or intravenous GnRH antagonist. LH concentration for the altrenogest group was lower than the control group at 3, 4, 18, and 30 hours after treatment (P < .05). LH concentration for both the subcutaneous and intravenous GnRH antagonist groups were lower compared with the control group at several time points (P < .05). Based on these data, dose but not frequency of administration of a GnRH antagonist lowered LH concentration in the estrous mare but did not delay ovulation. In addition, serum LH concentrations can be lowered and ovulation effectively postponed in mares treated with altrenogest followed by administration of hCG. This indicates that serum LH concentrations can be lowered and ovulation effectively postponed in mares treated with altrenogest followed by administration of hCG.