Cryopreserved-thawed embryo transfer in natural or down-regulated hormonally controlled cycles: a retrospective study

Objective To assess the implantation, pregnancy, and live birth rates after the transfer of frozen-thawed embryos (FET) in a natural or hormonal control cycle. Design Retrospective study. Setting National Health Service tertiary referral center for reproductive medicine in Manchester, United Kingdom. Patient(s) Two comparable groups of women with regular menstrual cycles: Group A (n = 212) had FET in a natural cycle after spontaneous ovulation; group B (n = 205) had FET in a pituitary-desensitized hormonally controlled cycle. Intervention(s) In group B, GnRH agonist was commenced in the midluteal phase of the previous cycle and discontinued 3 days before embryo transfer. Oral estradiol valerate and vaginal progesterone pessary were used to prepare the endometrium. Embryo transfer was carried out 3 days after detection of the endogenous LH surge in group A and on day 3 of progesterone administration in group B. Main Outcome Measure(s) Implantation, pregnancy, and live birth rates per cycle and per embryo transfer (ET). Result(s) In the 212 women who had natural-cycle FET, 172 ETs were performed and 247 embryos replaced. The implantation rate was 14.1% (35/247). Twenty clinical pregnancies (20/172, 11.6%) were achieved. In the 205 women who had down-regulated hormone replacement–cycle FET, 173 embryo transfers were performed and 243 embryos replaced. The implantation rate was 13.5% (33/243). Eighteen clinical pregnancies (18/173, 10.2%) were achieved. There were no significant differences between the two groups with regard to the implantation, clinical pregnancy, or live birth rates per cycle or per ET. Conclusion(s) These findings suggest that both FET protocols are equally effective in terms of implantation rate and pregnancy outcome in women with regular menstrual cycles.