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.