Clinical outcomes of co-transfer of partially and fully compacted morula versus fully compacted morula alone on day 4

To evaluate the impact of day 4 double embryo transfer (DET) with a fully compacted morula (FCM) and a partially compacted morula (PCM) versus day 4 single embryo transfer (SET) with an FCM on clinical and neonatal outcomes in fresh cycles.

This was a retrospective cohort study including 889 fresh day 4 embryo transfer cycles conducted between October 2018 and December 2024. Propensity score matching (PSM) was applied to control for potential confounders and compare the clinical outcomes between SET with FCM and DET with FCM and PCM.

After PSM, logistic regression analysis showed no significant differences in clinical pregnancy rate (CPR), miscarriage rate, live birth rate (LBR), cumulative live birth rate (CLBR), monozygotic twin rate, stillbirth rate, and cesarean section rate (CSR) (all P > 0.05). However, the DET with FCM and PCM group was associated with a significantly higher multiple pregnancy rate (MPR) (P < 0.001) and preterm delivery rate (PDR) (OR 4.02, 95% CI 1.75-9.22; P = 0.001) after matching. Among patients aged<35 years or undergoing IVF, the pregnancy and neonatal outcomes were consistent with the overall data presented above. Specifically, following logistic regression analysis, there were no significant differences in CPR, LBR, and CLBR between the two groups(all P > 0.05), but the MPR in the DET with FCM and PCM group was significantly higher(all P<0.001). Furthermore, after excluding early-stage blastocysts, the clinical and neonatal outcomes remained consistent with the main study findings.

In fresh cycles, there were no significant differences in CPR, LBR and CLBR following day 4 DET with FCM and PCM compared with SET with FCM. However, the MPR was significantly higher in the DET group. SET with FCM may be a preferable strategy for balancing clinical and multiple pregnancy rates.