Singleton and twin physical development after blastocyst or cleavage-stage embryo transfer: A retrospective cohort

To compare fetal and postnatal physical development parameters up to 3 years after blastocyst embryo transfer (BET) versus cleavage-stage embryo transfer (CET) in singleton and twin offspring.

We included 530 pregnancies: 331 singletons (BET, n = 171; CET, n = 160) and 199 twins (BET, n = 110; CET, n = 89). Longitudinal fetal biometric and postnatal anthropometric parameters were analyzed separately in singletons and twins using linear mixed-effects models including embryo transfer strategy, time, and their interaction, with covariate adjustment and appropriate random effects. Time-specific BET-CET contrasts used estimated marginal means with Holm adjustment. Analyses were exploratory; Benjamini-Hochberg false discovery rate correction and frozen-transfer sensitivity analyses were also performed.

Among twins, most fetal biometric parameters were comparable between BET and CET, except humerus length, which showed a significant interaction and was greater after BET at 14-21 weeks. Among singletons, several fetal parameters showed significant interactions; after Holm adjustment, abdominal circumference and estimated fetal weight were greater after BET at ≥ 37 weeks. Postnatally, weight, height, and head circumference showed significant group-by-age interactions in both strata, with greater weight and height at later ages after BET. Principal interaction findings remained significant after false discovery rate correction and were largely supported by frozen-transfer sensitivity analyses.

BET was associated with modest differences in selected fetal biometric and postnatal anthropometric parameters compared with CET. The most consistent findings involved late-gestational fetal parameters in singletons and postnatal weight and height in both strata.