Serum progesterone concentrations are reduced in obese women on the day of embryo transfer

Research question: Does serum progesterone concentration vary on the day of embryo transfer according to female body mass index (BMI)? Design: Retrospective analysis including 3210 infertile patients undergoing an embryo transfer in the context of an artificial endometrial preparation cycle with sequential administration of oestrogens and micronized vaginal progesterone (MVP) (400 mg/12 h). Serum progesterone was measured on the day of embryo transfer, 6 +/- 2 h after last MVP administration. Serum progesterone concentrations were subdivided into optimal (>= 9.2 ng/ml) or suboptimal (<9.2 ng/ml) concentrations, and the cut-off point was defined according to our previous results. The primary objective was the correlation between progesterone concentrations on the day of embryo transfer and patient BMI, as a continuous variable and according to four ranges (underweight: <18.5 kg/m(2); normal weight: 18.5-24.9 kg/m(2); overweight: 25-29.9 kg/m(2); and obesity: >= 30 kg/m(2)), according to the World Health Organization classification. Secondary objectives included the evaluation of reproductive outcome according to patient BMI and progesterone concentrations on the day of embryo transfer. Results: Mean serum progesterone concentrations and the ratio of patients with progesterone concentrations above the cut-off point of 9.2 ng/ml fell progressively as BMI increased. Overweight and obese patients had lower mean serum progesterone concentrations than underweight and normal weight women (P < 0.001). A trend was observed towards impaired reproductive results in obese patients with suboptimal progesterone concentrations, absent when concentrations were optimal. Conclusions: Serum progesterone concentrations on the day of embryo transfer in artificial cycles with MPV decrease as BMI increases. It is highly recommended that serum progesterone concentrations are moitored to ensure optimal concentrations and reproductive outcomes.