Relationship between the day of embryo transfer and the outcome in human in vitro fertilization and embryo transfer

Purpose To clarify the optimal date of embryo transfer (ET), we retrospectively analyzed the relationship between the day of ET and the outcome in human in vitro fertilization and embryo transfer (IVF-ET).Method Of a total of 307 human IVF-ET cycles performed at Kyoto University Hospital between January 1990 and March 1994, we focused on 207 cases of IVF-ET cycles in which two or three good-quality embryos were transferred. These 207 IVF-ET cycles consisted of 54 Day 2 ET cycles, 79 Day 3 ET cycles, 46 Day 4 ET cycles, and 28 Day 5 ET cycles. We compared the pregnancy and live-birth (plus ongoing pregnancy) rates among these four ET groups.Results The pregnancy rates of ET on Days 2 to 4 were not significantly different, whereas Day 5 ET produced a significantly lower pregnancy rate (Day 2, 29.6%; Day 3, 32.9%; Day 4, 30.4%; Day 5, 10.7%). Similar results were obtained for the live-birth (plus ongoing pregnancy) rates (Day 2, 20.3%; Day 3, 18.9%; Day 4, 17.9%; Day 5, 7.1%).Conclusions These results suggest that the day of ET does not fundamentally affect the pregnancy rate in human IVF-ET provided that transfer is made before Day 5.