Neonatal outcome and birth defects in 6623 singletons born following minimal ovarian stimulation and vitrified versus fresh single embryo transfer.

OBJECTIVE: To compare neonatal outcome between children born after vitrified versus fresh single-embryo transfer (SET).

STUDY DESIGN: Retrospective, single-centre cohort study of 6623 delivered singletons following 29,944 single-embryo transfers. Patients underwent minimal ovarian stimulation/natural cycle IVF followed by SET of fresh or vitrified-warmed (using Cryotop, Kitazato) cleavage-stage embryos or blastocysts. Outcome measures were gestational age at delivery, birth weight, birth length, low birth weight (LBW), small for gestational age (SGA) and large for gestational age (LGA) infants, perinatal mortality and minor/major birth defects (evaluated by parent questionnaire).

RESULTS: Gestational age (38.6 ± 2 versus 38.7 ± 1.9 weeks) and preterm delivery rate (6.9% versus 6.9%, aOR: 0.96 95%CI: 0.76-1.22) in singletons born after the transfer of vitrified embryos were comparable to those born after the transfer of fresh embryos. Children born after the transfer of vitrified embryos had a higher birth weight (3028 ± 465 versus 2943 ± 470 g, p<0.0001) and lower LBW (8.5% versus 11.9%, aOR: 0.65 95%CI: 0.53-0.79) and SGA (3.6% versus 7.6% aOR: 0.43 95%CI: 0.33-0.56) rates. Total birth defect rates (including minor anomalies) (2.4% versus 1.9%, aOR: 1.41 95%CI: 0.96-2.10) and perinatal mortality rates (0.6% versus 0.5%, aOR: 1.02 95%CI: 0.21-4.85) were comparable between the vitrified and fresh groups.

CONCLUSIONS: Vitrification of embryos/blastocysts did not increase the incidence of adverse neonatal outcomes or birth defects following single embryo transfer.