THE WINDOW FOR EMBRYO-TRANSFER IN OOCYTE DONATION CYCLES DEPENDS ON THE DURATION OF PROGESTERONE THERAPY

In 192 oocyte donation cycles performed between January 1993 and July 1996, we examined the width of 'the window for embryo transfer' using standard hormonal replacement methods, All transfers mere performed wi thin 48 h of insemination. We varied the day of embryo transfer,vith r egard to the initiation of progesterone therapy and, thus, the duratio n of endometrial exposure to progesterone and analysed the resulting p regnancy rates. Patients mere divided into five groups (I-V) and embry o transfers were performed 2, 3, 4, 5 or 6 days following initiation o f progesterone therapy. The number of pregnancies per transfer cycle a chieved in groups I-V were 0 (0%), 3 (12%), 16 (40%), 29 (48.3%), and 10 (20.4%) respectively. The increased pregnancy rate in group III in comparison to group II is statistically significant (P < 0.03). Furthe rmore, the pregnancy rate in group IV (5 days of progesterone administ ration before embryo transfer) was significantly higher than in group V (6 days of progesterone administration before embryo transfer; P < 0 .005). We also noted that, when embryos were transferred 4 or 5 days a fter initiation of progesterone therapy, the pregnancy rates were not significantly different between menopausal and cycling recipients (50% vs 43.7%). Our results indicate that the window for embryo transfer i s dependent on duration of treatment with progesterone; it begins appr oximately 48 h after starting progesterone administration and lasts fo r approximately 4 days. The optimum period for transferring embryos at the 4- to 8-cell stage corresponds to cycle days 18 and 19, Transfers performed on the 17th and 20th days of the cycle can result in succes sful implantation, although the rates of implantation are highest when transfers are done on days 18 and 19.