O-086 Assisted reproductive technology does not influence body mass index (BMI) in a cohort of 606 children aged 6-9 years
Authors: Asserhøj L L , Mizrak I , Clausen T , Greisen G , Main K , Madsen P L , Jensen R B , Pinborg A 
Published: June 2022

Abstract

Study question
Is BMI in children conceived after frozen embryo transfer different from children conceived after fresh embryo transfer and after natural conception?

Summary answer
BMI in children conceived after frozen embryo transfer was similar to BMI in children conceived after fresh embryo transfer or children born after natural conception.

What is known already
Children conceived after frozen embryo transfer (FET) have higher risk of being born large for gestational age (LGA) than children conceived after natural conception (NC). Generally, being born LGA increases the risk of obesity in childhood. Childhood BMI is strongly associated with obesity and cardiometabolic disease and mortality in adulthood.
The long-term effects of ART on the metabolic health of the offspring and the underlying mechanisms are scarcely explored. However, it has been proposed that ART may induce epigenetic variations around fertilization, implantation, and early embryonic stages that may influence size at birth.

Study design, size, duration
The study “Health in Childhood following Assisted Reproductive Technology” (HiCART) includes 606 singletons (292 boys, 314 girls) – 200 conceived after FET; 203 after fresh-ET; and a random sample of 203 naturally conceived children matched for age and sex. All children were born in Eastern Denmark from 2009-2013 and had a clinical examination performed at the Copenhagen University Hospital - Rigshospitalet when they were 6-9 years of age.

Participants/materials, setting, methods
The children underwent a clinical examination with anthropometric measurements, whole-body dual-energy x-ray absorptiometry-scan (DXA), pubertal staging, and a blood sample. All anthropometric measurements were converted to standard deviation scores (SDS) using a Danish reference. Parents filled in a questionnaire regarding the pregnancy and the current health of the child and themselves. Maternal, obstetric and neonatal data from the national ART and birth registry were obtained.

Main results and the role of chance
Children conceived after FET had higher birthweight SDS (0.20SDS, 1.09SD) than children conceived after fresh-ET (-0.22SDS, 1.00SD), p &lt; 0.001 and children conceived naturally (-0.16SDS, 1.09SD), p = 0.001. Mothers conceiving naturally were younger and had higher parity than mothers conceiving after ART. The three groups were similar regarding pregestational maternal BMI and gestational age.
Puberty had started in 57 children (54 girls), evenly distributed among the groups.
There were no differences in height SDS between FET (0.25SDS, 1.00SD) compared to fresh-ET (0.17SDS, 0.96SD), p = 0.50 and compared to NC (0.07 SDS, 1.06SD), p = 0.11 or in weight SDS between FET (0.22SDS, 1.07SD) compared to fresh-ET (0.10 SDS, 1.06SD), p = 0.22 and compared to NC (0.14SDS, 1.00SD), p = 0.43. Similarly, no differences were found in BMI SDS between FET (0.16SDS, 1.16SD) compared to fresh-ET (0.04SDS, 1.10SD), p = 0.25 and compared to NC (0.20SDS, 1.01SD), p = 0.80. Our primary endpoint BMI SDS remained non-significant after adjustment for child sex, age and birthweight SDS, parity, maternal BMI and smoking in pregnancy.

Limitations, reasons for caution
The sample size was decided to be able to detect a difference of 0.3 SDS in childhood BMI, corresponding to a 3.4% increased mortality hazard. Thus, smaller differences in BMI SDS may be overlooked. As the participation rate was between 18-42% in the three groups, selection bias cannot be excluded.

Wider implications of the findings
The increased birth weight in children conceived after FET did not translate into a difference in BMI in this large cohort. Since BMI in childhood is a strong biomarker of cardiometabolic disease later in life, the findings are reassuring and may reduce concerns associated with the long-term consequences of FET.

Trial registration number
NCT03719703