The timing for initiating estrogen stimulation in artificial cycle for frozen-thawed embryo transfer can be flexible

Abstract

Background

There remains a lack of evidence to demonstrate whether the initiation time of estrogen stimulation is flexible in the proliferative endometrial phase during the artificial cycle for frozen-thawed embryo transfer (AC-FET).

Methods

FET records were retrospectively reviewed from a large university-affiliated reproductive medicine center. Only the patients who were undergoing their first embryo transfer with a single blastocyst in the AC-FET cycles were included: thereby 660 cycles were recruited, and the patients were grouped according to their day of estrogen usage initiation as early initiation group (estrogen stimulation initiated during days 2–5 of menses, n = 128) and the late initiation group (estrogen stimulation initiated on or after the 6th day of menses, n = 532). The primary outcome was the ongoing pregnancy rates (OPR).

Results

The rates of biochemical and clinical pregnancies were significantly higher in the late initiation group relative to those in the early initiation group, however, no significant differences were noted between the two groups for OPR. Furthermore, after adjusting for the results of the potential confounders, no impact was observed in the initiation time of estrogen stimulation on the OPR.

Conclusions

This study provides evidence that initiating the estrogen stimulation on after days 2–5 of menses do not exert adverse effects on the OPR in AC-FETs. Thus, AC-FET can be scheduled in a flexible manner without compromising on the pregnancy outcomes.

Plain Language summary

Despite the continuous efforts invested in exploring and optimizing therapeutic regimens to improve the success rate of frozen-thawed embryo transfer (FET), we found that there are little evidence to demonstrate whether the initiation time of estrogen stimulation is flexible in the proliferative endometrial phase during the artificial cycle for FET (AC-FET). Thus, we retrospectively reviewed the FET records from a large university-affiliated reproductive medicine center to explore whether the relatively late start of endometrial stimulation for FET influences the pregnancy outcome. Results provided evidences that initiating the estrogen stimulation on after days 2–5 of menses do not exert adverse effects on the ongoing pregnancy rates in AC-FETs. Therefore, FET can be scheduled in a flexible manner, according to the ovulatory and endometrial statuses and patient and/or clinic preference, without compromised clinical outcomes.