Comparison of stimulated versus modified natural cycles for endometrial preparation prior to frozen embryo transfer: a randomized controlled trial

Abstract

Research question: To compare stimulated cycle (STC) versus modified natural cycle (MNC) for endometrial preparation prior to frozen embryo transfer (FET) in terms of convenience and efficacy.

Design: Prospective, open-label, randomized controlled study including 119 patients aged 20-38 years, undergoing intra-conjugal IVF/intracytoplasmic sperm injection, having regular cycles, at least two day 2 or day 3 frozen embryos, for whom it was the first or second FET performed, randomized to either MNC (n = 59) or STC (n = 60). Monitoring consisted of ultrasound and hormonal measurements. The number of monitoring visits required was compared between the two groups.

Results: STC required a significantly lower number of monitoring visits compared with MNC (3.6 ± 0.9 versus 4.4 ± 1.1, respectively, P < 0.0001), a lower number of blood tests (2.7 ± 0.8 versus 3.5 ± 1.0, respectively, P < 0.0001) and of ultrasounds (1.2 ± 0.4 versus 1.5 ± 0.6, respectively, P = 0.0039). FET during 'non-opening' hours (22.6% versus 27.5%, respectively, P = 0.32) and cancellation rates (11.7% versus 11.9%, respectively, P = 0.97) were comparable between the STC and MNC groups. No difference concerning HCG-positive rates (34.0% versus 23.1%, respectively, P = 0.22) nor live birth rates (24.5% for STC versus 23.1% for MNC, respectively, P = 0.86) was observed. Quality of life as defined by the FertiQol score was not different (P > 0.05 for each item).

Conclusion: Altogether, these findings can be used for everyday clinical practice to better inform patients when deciding on the protocol to use for FET. These results suggest that MNC is a good option for patients reluctant to have injections, but requires increased monitoring. STC may offer more flexibility for patients and IVF centres.

Keywords: Endometrial preparation; FertiQol; Frozen embryo transfer; Modified natural cycle; Stimulated cycle.