A comparative study of the effects of two different treatment periods with estradiol in endometrial preparation on the pregnancy outcome of frozen embryos

Currently, there is disagreement regarding the duration of treatment with estradiol in the cycle of frozen embryo transfer and its effect on pregnancy outcomes. The present study was performed with aim to compare the duration of treatment with estradiol in the endometrial preparation in the freezing embryo transfer cycle and its effect on pregnancy outcomes in infertile women.

This randomized controlled clinical trial study was performed in 2021 on 140 infertile women candidate for assisted reproductive technology by frozen embryo transfer. The subjects were randomly allocated into two groups: intervention (estradiol recipient, for 8 days) and control (recipient of estradiol as usual, 13 days). In the intervention group, progesterone was started from the eighth day of estradiol intake and in the control group from the thirteenth day of estradiol intake. In both groups, estradiol and progesterone levels were measured the day before progesterone onset and then the embryos were transferred in the morula or blastocyst stage. Data analysis was done using SPSS statistical software (version 26) and chi-square and t-test.  P<0.05 was considered statistically significant.

In the intervention and control groups, the mean serum level of estradiol during embryo transfer was 285.7 ±287.1 and 443.5 ±354.3 (P = 0.028), the mean endometrial thickness at the time of progesterone onset was 9.3 ±1.4 and 8.8 ±0.9 mm (P = 0.008), frequency of chemical pregnancy occurrence was 31.4% and 17.1% (OR = 1.1, P = 0.049) and frequency of clinical pregnancy was 27.1% and 17.1% (OR = 1.4, P = 0.154) respectively.

In infertile women treated with IVF assisted reproductive technology, shorter duration of treatment with estradiol in endometrial preparation and frozen embryo transfer cycle are associated with better pregnancy outcomes.