Extended culture may contribute to poor intellectual performance of children born after frozen embryo transfer

Summary: Frozen embryo transfer (FET) is becoming popular in recent years. However, whether embryos freezing or other factors may affect intellectual performance in offspring is still unknown. We compared the Wechsler Intelligence Scale for Children Fourth Edition (WISC-IV) questionnaire scores between children born after fresh embryo transfer (fresh ET) and FET. They were matched in a 1:1 ratio on their sex and age (±1 month). 326 children were included in each group. We found children born after FET scored lower on the WISC-IV questionnaire (p = 0.002). In subgroup analysis, the full-scale scores are similar between fresh ET and FET in the cleavage-stage transfer group (p = 0.57). In the FET group, the blastocyst-stage transfer group had lower full-scale scores compared with the cleavage-stage transfer group (p = 0.004). Children born after FET scored lower on WISC-IV questionnaire might be linked to extended culture of embryos rather than the freezing process.