Progesterone supplementation increases luteal phase endometrial thickness and oestradiol levels in in-vitro...

Luteal phase supplementation with natural progesterone appears to increase the pregnancy rate in in-vitro fertilization (IVF). The objective of this investigation was to examine the effect of intravaginal progesterone on endometrial thickness and hormonal parameters 7-9 days after embryo transfer. IVF patients receiving progesterone supplementation (Prog +, n = 64), who did not conceive, were compared to patients not receiving progesterone (Prog -, n = 23) because of failed fertilization. These two groups were also compared to 20 women (Preg) who conceived and to 16 women (control) in the mid-luteal phase of natural cycles. Endometrial thickness was greater (P < 0.01) in the Prog + (0.88 +/- 0.04 cm) and Preg (0.92 +/- 0.02 cm) groups compared to the Prog - (0.71 +/- 0.05 cm) and control (0.65 +/- 0.05 cm) groups. Mean luteal phase serum oestradiol levels were also higher (P < 0.05) in the Prog + (1118 +/- 112 pmol/l) and Preg (2267 +/- 757 pmol/l) groups than in the Prog - (574 +/- 70 pmol/l) and control (468 +/- 38 pmol/l) groups. These findings suggest that progesterone supplementation may affect pregnancy rates in IVF by increasing endometrial thickness, thereby enhancing receptivity for implantation. The mechanism through which this effect occurs is unclear but may involve serum oestradiol elevation.