Comparison of pregnancy outcomes between 4th day morula and 5th day blastocyst after embryo transfer:a retrospective cohort study

Abstract

Abstract Background This study was designed to evaluate pregnancy outcomes between morulae transferred on day 4 (D4) and blastocysts transferred on day 5 (D5). Methods From September 2017 to September 2020, 1963 fresh transfer cycles that underwent early follicular phase extra-long protocol for assisted conception in our fertility center were divided into D4 (324 cases) and D5 (1639 cases) groups based on the number of days of in vitro culture after fertilization, and the general basic information, clinical and embryonic conditions of patients in both groups were compared. To compare the differences in pregnancy outcomes, the D4 and D5 groups were further divided into groups A and B based on single and double embryo transfer. Results In single embryo transfer, there was no significant difference between groups D4A and D5A (P > 0.05). In double embryo transfer, group D4B had a lower newborn birthweight and a larger proportion of low birthweight infants (P < 0.05). The preterm delivery rate, twin delivery rate, cesarean delivery rate, and percentage of low birthweight infants were lower in the D5A group than in the D5B group (P < 0.05). Conclusion When factors such as working life and hospital holidays are being considered, D4 morula transfer may be a good alternative to D5 blastocyst transfer. Given the in vitro fertilization/intracytoplasmic sperm injection(IVF/ICSI) success rate and risk of twin pregnancy, D4 morula transfer requires an adapted decision between single and double embryo transfer, although a single blastocyst transfer is recommended for the D5 transfer in order to decrease the twin pregnancy rate.