Does increasing estrogen dose during frozen embryo transfer affect pregnancy rate?

Abstract

To assess the effect of increasing estrogen doses during hormone therapy frozen embryo transfer (HT-FET) cycles on endometrial thickness and success rates compared to patients who received fixed estrogen dose. A retrospective study from a university-based fertility clinic during the years 2008-2021. We compared two groups: the fixed-dose group (i.e., received 6mg estradiol dose daily until embryo transfer) and the increased-dose group (i.e., the initial estradiol dose was 6mg daily, and was increased during the cycle). clinical pregnancy rate. The study included 5452 cycles of HT-FET: 4774 cycles in the fixed-dose group and 678 cycles in the increased-dose group. Ultrasound scan on days 2-3 of the cycle showed endometrial thickness slightly different between the two groups (4.2mm in the fixed-dose and 4.0mm in the increased-dose group, P = 0.003). The total estrogen dose was higher, and the treatment duration was longer in the increased than the fixed-dose group (122mg vs. 66mg and 17days vs. 11days, respectively; P < 0.001). The last ultrasound scan done before the addition of progesterone showed that the endometrial thickness was significantly thicker in the fixed than the increased-dose group (9.5mm vs. 8.3mm; P < 0.001). The clinical pregnancy rates were 35.8% in the increased-group vs. 34.1% in the fixed-dose group; P = 0.401. The increased-dose group had thinner endometrium despite the higher doses of estrogen and longer treatment duration than the fixed-dose group. However, the pregnancy rates were similar between the two groups.