Effect of reculture of the thawed slowly developing embryos before transfer on implantation and pregnancy; a Randomized Controlled Study
Background: Embryos resulting from assisted reproduction techniques and cultured to reach the day 5 Fully Expanded Blastocyst stage (FEB). For some reasons, embryos may have delayed division and development. In a fresh embryo transfer cycles using these embryos, pregnancy rates are expected to drop significantly due to defective embryo-endometrial synchronization. A proposed approach is to freeze these embryos then thaw and reculture for 24 hours before embryo transfer as an attempt to enhance embryo development to reach FEB before embryo transfer.
Methods: It is a prospective randomized controlled study, including 60 women undergoing FET in Shatby university hospital and one private IVF center. Endometrial preparation was done using estradiol valerate supplementation and luteal phase support using a combination of vaginal and intramuscular progesterone. Then women were randomized to FET either after 24 hours of reculturing of thawed embryos (group 1, n = 30) or on the same day of embryo thawing (group 2, n =30).
Results: Out of 54 embryo transferred in 30 FET cycles in group 1, 18 intrauterine gestational sacs with pulsating fetal poles were observed using transvaginal ultrasound (33% implantation rate) and 13 of these progressed till beyond 12 weeks of gestation (24.1% ongoing pregnancy rate). However, a total of 84 embryo were transferred in 30 FET cycles in group 2, of which 16 intrauterine gestational sacs with pulsating fetal poles were observed using transvaginal ultrasound (19.3% implantation rate) and 10 of these progressed till beyond 12 weeks of gestation (12 % ongoing pregnancy rate). No statistically significant difference was observed (P 0.063, 0.066).
Conclusion: Deferring embryo transfer and reculturing till reaching a fully expanded embryos for later vitrified-warmed transfer may improve the LBRs, although further studies are needed to clarify this hypothesis.