Objective Recent genome-wide association studies have identified FTO as a candidate gene for obesity. Studies have shown that this gene is also associated with childhood obesity. We hypothesized that FTO polymorphism rs8050136 influences prenatal and early postnatal growth.

Methods This study was embedded in the Generation R study, a population-based prospective cohort study from fetal life until young adulthood. Fetal growth was assessed by ultrasound in early, mid-, and late pregnancy. Anthropometrics in infancy were assessed at birth and at the ages of 1.5, 6, 11, 14 and 18 months. FTO rs8050136 genotyping was performed in 3372 children of Caucasian ethnicity. Additionally, dual-energy x-ray absorptiometry (DXA) was performed at 6 months in 200 children.

Results Genotype frequency distribution was 37.8% (C/C), 47.8% (C/A), and 14.7% (A/A). Using dominant models, the variant genotype (A/A) was not associated with estimated fetal weight, birth weight (difference: 31 grams (95% CI −10 to 73)), or postnatal weight (difference at 18 months: −63 grams (95% CI −218 to 90)). No significant differences were found in height or head circumference either. Finally, FTO genotype was not associated with body composition at 6 months using DXA. Similar effect estimates were found using additive models.

Conclusions This study suggests that FTO rs8050136 is not associated with body composition or fetal and early postnatal growth. The previously found association with (childhood) obesity may start after the first 18 months of life.