Risk of severe ovarian hyperstimulation syndrome in GnRH antagonist versus GnRH agonist protocol: RCT including 1050 first IVF/ICSI cycles

Study question: Is the risk of severe ovarian hyperstimulation syndrome (OHSS) similar in a short GnRH antagonist and long GnRH agonist protocol in first cycle IVF/ICSI patients less than 40 years of age?.

Summary answer: There is an increased risk of severe OHSS in the long GnRH agonist group compared with the short GnRH antagonist protocol. WHAT IS KNOWN ALREADY?: In the most recent Cochrane review, the GnRH antagonist protocol was associated with a similar live birth rate (LBR), a similar on-going pregnancy rate (OPR), and a lower incidence of OHSS (odds ratio (OR) = 0.43 95% confidence interval (CI): 0.33-0.57) compared with the traditional GnRH agonist protocol. Previous trials comparing the two protocols mainly included selected patient populations, a limited number of patients and the applied OHSS criteria differed, making direct comparisons difficult. In two recent large meta-analyses, no significant differences in LBR (OR = 0.86; 95% CI: 0.72-1.02) or in the incidence of severe OHSS were reported, while others found a lower LBR (OR = 0.82; 95% CI: 0.68-0.97) and a reduced risk of severe OHSS using the GnRH antagonist protocol (OR = 0.60; 95% CI: 0.40-0.88).

Study design, size, duration: Phase IV, dual-centre, open-label, RCT including 1050 women allocated to either short GnRH antagonist or long GnRH agonist protocol in a 1:1 ratio and enrolled over a 5-year period using a web-based concealed randomization code. This is a superiority study designed to detect a difference in severe OHSS, the primary outcome, between the two groups with a power of 80% and stratified for age, assisted reproductive technology (ART) clinic and planned fertilization procedure (IVF/ICSI). The secondary aims were to compare rates of mild and moderate OHSS, positive plasma (p)-hCG, on-going pregnancy and live birth between the two arms. None of the women had undergone previous ART treatment.

Participants/materials, setting, methods: All infertile women referred for their first IVF/ICSI at two public fertility clinics, less than 40 years of age and with no uterine malformations were asked to participate. A total of 1099 subjects were randomized, including women with poor ovarian reserve, polycystic ovary syndrome and irregular cycles. A total of 49 women withdrew their consent, thus 1050 subjects were allocated to the GnRH antagonist (n = 534) and agonist protocol (n = 516), respectively. In total 1023 women started recombinant human follitropin-β (rFSH) stimulation, 528 in the GnRH antagonist group and 495 in the GnRH agonist group. All subjects were given a fixed rFSH dose of 150 IU or 225 IU according to age ≤36 years or >36 years, with the option to adjust dose at stimulation day 6. Clinical OHSS parameters were collected at oocyte retrieval, and Days 3 and 14 post-transfer. On-going pregnancy was determined by transvaginal ultrasonography at gestational weeks 7-9. In the intention-to-treat (ITT) analysis for reproductive outcomes, 1050 subjects were included. For the ITT analyses on OHSS 1023 subjects who started gonadotrophin stimulation were included.

Main results and the role of chance: The incidence of severe OHSS [5.1% (27/528) versus 8.9% (44/495) (difference in proportion percentage point (Δpp) = -3.8pp; 95% CI: -7.1 to -0.4; P = 0.02)] and moderate OHSS [10.2% (54/528) versus 15.6% (77/495) (Δpp = -5.3pp; 95% CI: -9.6 to -1.0; P = 0.01) ] was significantly lower in the GnRH antagonist group compared with the agonist group, respectively. In the GnRH antagonist and agonist group, respectively, 4.7% (25/528) versus 8.5% (42/495) women were seen by a physician due to OHSS (P = 0.01), and 1.7% (9/528) versus 3.6% (18/495) were admitted to hospital due to OHSS (P = 0.06). No women had ascites-puncture in the GnRH antagonist group versus 2.0% (10/495) in the GnRH agonist group (P < 0.01). LBRs were 22.8% (122/534) versus 23.8% (123/516) (Δpp = -1.0pp; 95% CI: -6.3 to 4.3; P = 0.70) and OPRs were 24.9% (133/528) versus 26.2% (135/516) (Δpp = -1.3pp; 95% CI: -6.7 to 4.2; P = 0.64) per randomized subject in the GnRH antagonist versus agonist group, with a mean number of 1.1 versus 1.2 embryos transferred in the two groups. Pregnancy rates (PR) per randomized subject, per started gonadotrophin stimulation and per embryo transfer were all similar in the two groups.

Limitations, reasons for caution: A possible limitation is the duration of the trial, with new methods, such as 'freeze all' and 'GnRH agonist triggering', being developed during the trial, the new methods were sought avoided, however a total number of 32 women had 'freeze all' and 'GnRH agonist triggering' was performed in three cases. Ultrasonic measurements were performed by different physicians and inter-observer bias may be present. Measures of anti-Mullerian hormone and antral follicle count, to estimate ovarian reserve and thus predict risk of OHSS, were not performed. Finally, the physicians were not blinded to GnRH treatment group after randomization.

Wider implications of the findings: The short GnRH antagonist protocol should be the protocol of choice for patients undergoing their first ART cycle in females <40 years of age including both low and high responders when an age-dependent initially fixed gonadotrophin dose is used, as an increased risk of severe OHSS and the associated complications is seen in the long GnRH agonist group and as PRs and LBRs are similar in the two groups. Patients at risk of OHSS particularly benefit from the short GnRH antagonist treatment as GnRH agonist triggering can be used.

Study funding/competing interests: An unrestricted research grant is funded by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (MSD). The funders had no influence on the data collection, analyses or conclusions of the study. No conflict of interests to declare.

Trial registration number: EudraCT #: 2008-005452-24. ClinicalTrial.gov: NCT00756028. Trial registration date: 18 September 2008. Date of first patient's enrolment: 14 January 2009.