Chemical pregnancy in fresh and cryopreserved cycles, using day 3 (cleavage stage) and day 4 embryos (morula stage)

With the advancement in the embryo culture media, which supports nutrient requirements of embryos up to 5 to 6 days, there's a chance to select more viable embryos, which are more likely to result in pregnancy, compared to earlier stages. Also, there is a controversy regarding the frozen embryo transfer compared to the fresh type. To compare the chemical pregnancy rates between fresh embryo transfer (ET), and frozen embryo transfer (FET), on day 3 (cleavage), and day 4 (morula) of development. In this retrospective study, data of 242 fresh and 758 frozen embryo transfer cycles were obtained in one infertility center in Isfahan, Iran. The study's groups were assigned based on the day of fresh or frozen embryo transfer (day 3, or day 4 embryos) and the embryo grading. Chemical pregnancy was the main outcome measurement (implantation rates). The chemical pregnancy rate was higher in the good quality frozen embryo day 3 and transfer on day 4 group (40.1%). This rate was near the results of transferring the good quality frozen embryo on day 4 (39.2 %). There was no significant difference in the chemical pregnancy rate related to the number of transferred embryos (p = 0.55). The higher PRs, when the embryos were transferred on day 4, provided further support for the morula stage embryo transfer, possibly because of better synchrony with the endometrium. It is concluded that morula/compact embryos are good candidates for embryo transfer, which simultaneously reduces the number of transferred embryos.