Elective single morula transfer achieved better clinical outcomes than two cleavage embryos transfer in fresh IVF-ET cycles.

BACKGROUND: Assisted reproductive technology (ART) effectively treats infertility yet often results in multiple pregnancies. Optimizing clinical pregnancy rates while minimizing multiples remains challenging. Key considerations for ART providers include embryo transfer timing, number, and developmental stage. While double cleavage-stage and single blastocyst transfers are common, limited data exists on the intermediate strategy of single morula transfer. OBJECTIVE: This research aimed to assess whether elective single morula transfer (eSMT) on Day 4 yields clinical outcomes comparable to double cleavage-stage embryo transfer (DCT) on Day 3. METHODS: A retrospective propensity-matched cohort study compared DCT and eSMT in IVF, with 156 matched cases per group. Primary outcomes included clinical pregnancy rate (CPR), live birth rate (LBR), twin pregnancy rate, and preterm delivery rate. Secondary outcomes were abortion rate (AR) and cesarean section rate. RESULTS: After propensity score matching, no significant differences were observed between DCT and eSMT groups in CPR (75.00% vs. 69.23%), AR (16.24% vs. 14.81%), LBR (59.62% vs. 58.97%), or cesarean rate (51.61% vs. 41.30%) (all P > 0.05). The eSMT group showed significantly lower preterm delivery rates (9.78% vs. 21.51%, P < 0.05) and higher single live birth rates (58.97% vs. 43.59%, P < 0.01). CONCLUSION: In patients aged ≤ 35 years, Day 4 single morula transfer demonstrates clinical pregnancy rates comparable to Day 3 double cleavage-stage embryo transfer while reducing twin pregnancy and preterm labor risks, thereby providing a safe individualized treatment strategy.