The combination of dydrogesterone and micronized vaginal progesterone can render serum progesterone level measurements on the day of embryo transfer and rescue attempts unnecessary in an HRT FET cycle.

PURPOSE:To evaluate the role of serum progesterone (P4) on the day of embryo transfer (ET) when dydrogesterone (DYD) and micronized vaginal progesterone (MVP) are combined as luteal phase support (LPS) in a hormone replacement therapy (HRT) frozen ET (FET) cycles. METHODS:Retrospective study, including single euploid HRT FET cycles with DYD and MVP as LPS and P4 measurement on ET day. Initially, patients with P4 levels < 10 ng/ml increased MVP to 400 mg/day; this "rescue" was abandoned later. RESULTS:560 cycles of 507 couples were included. In 275 women, serum P4 level was < 10 ng/ml on the ET day. Among those with low P4 levels, MVP dose remained unchanged in 65 women (11.6%) and was increased in 210 women (37.5%). Women with P4 levels ≥ 10 ng/ml continued LPS without modification. Overall pregnancy rates in these groups were 61.5% (40/65), 54.8% (115/210), and 48.4% (138/285), respectively (p = n.s.). Association of serum P4 levels with ongoing pregnancy rates was analyzed in women without any additional MVP regardless of serum P4 levels (n = 350); multivariable analysis (adjusted for age, BMI, embryo quality (EQ)) did not show a significant association of serum P4 levels with OPR (OR 0.96, 95% CI 0.90-1.02; p = 0.185). Using inverse probability treatment weights, regression analysis in the weighted sample showed no significant association between P4 treatment groups and OP. Compared to fair EQ, the transfer of good EQ increased (OR 1.61, 95% CI 1.22-2.15; p = 0.001) and the transfer of a poor EQ decreased the odds of OP (OR 0.73, 95% CI 0.55-0.97; p = 0.029). CONCLUSION:In HRT FET cycle, using LPS with 300 mg/day MVP and 30 mg/day DYD, it appears that serum P4 measurement and increase of MVP in patients with P4 < 10 ng/ml are not necessary.