Immediate versus delayed progesterone supplementation in gamete intrafallopian transfer (GIFT).

Exogenous progesterone (P) was supplemented to gamete intrafallopian transfer (GIFT) patients to determine the optimal timing to start P supplementation and the role of isthmic block in GIFT. Patients were alternatively divided into two groups. In the immediate group, exogenous P was supplied from the day of surgery. In the delayed group, P was supplied 4 days after the surgery, the day the fertilized ovum is supposed to arrive in the uterine cavity. Except for higher serum P levels on luteal day 3 in the immediate group, no significant differences were found in serum P levels during the early luteal phase, the pregnancy rate, and the abortion rate between the two groups. It is possible that in stimulated cycles, higher serum P levels during the early luteal phase render the endometrium receptive for embryo implantation, albeit unlock the isthmic block. It may not be crucial to start exogenous P supplementation either before or after a fertilized egg(s) arrives in the uterine cavity. The role of isthmic block in GIFT needs further evaluation.