G368(P) Does conception by in vitro fertilisation affect size in fetal life and early childhood?

Abstract

Aims Up to 2% of all pregnancies are conceived by in vitro fertilisation (IVF) in the UK. IVF methodologies include fresh and frozen-thawed embryo transfer. Neonates conceived by frozen-thawed IVF are at increased risk for high birth weight compared with peers born with fresh embryo transfer or without assisted conception. No study has described differences in anthropometric measurements before birth or in childhood between individuals conceived by IVF and without assistance. Here we test the hypothesis that individuals conceived by frozen-thawed IVF are larger as fetuses and neonates and also have increased childhood body mass index (BMI) compared with individuals not conceived by IVF. Methods Data from the Aberdeen Fertility Clinic, the Aberdeen Maternity and Neonatal Databank and the Study of Trends in Obesity in North East Scotland were linked between 1998 and 2012. Pregnancies conceived by non-IVF fertility treatment were excluded from the analysis. Fetal measurements from ultrasound scan data were adjusted for gestation and BMI at five years was standardised to the British 1990 reference population. Results Data were available in 66 717 pregnancies (330 IVF conceptions) in whom fetal size in the second and third trimester was measured in 18 014 and 6969 respectively, and measurements at birth and five years were available in 66 686 and 23 628 children respectively. IVF pregnancies had larger second trimester fetal size (mean z score difference 0.34 [0.17, 0.52]) and this difference was seen for both fresh and frozen-thawed embryo transfer Babies conceived after frozen-thawed (but not fresh) embryo transfer had increased mean z score birth weight (0.16 [0.01, 0.31]) and occiptofrontal circumference (0.15 [0.001, 0.30]) compared with babies conceived without IVF. There were no significant associations between method of conception and BMI, height and weight of children at five years. Conclusion There are subtle differences in early (fetal) size between individuals conceived by frozen-thawed embryo transfer compared with unassisted conception and these differences appear to resolve by five years of age.