Post-term birth is associated with greater risk of obesity in adolescent males.

Objective: To test the hypothesise that post-term birth (>42 weeks gestation) adversely affects longitudinal growth and weight gain throughout childhood.

Study Design: A total of 525 children (including 17 boys and 20 girls born post-term) were followed from birth to age 16 years. Weight and height were recorded prospectively throughout childhood, and respective velocities from birth to end of puberty were calculated using a mathematical model.

Results: At birth, post-term girls were slimmer than term girls (ponderal index, 27.7 ± 2.6 kg/m(3) vs 26.3 ± 2.8 kg/m(3); P<.05). At age 16 years, post-term boys were 11.8 kg heavier than term subjects (body mass index [BMI], 25.4 ± 5.5 kg/m(2) vs 21.7 ± 3.1 kg/m(2); P<.01). The rate of obesity was 29% in post-term boys and 7% in term boys (P<.01), and the combined rate of overweight and obesity was 47% in post-term boys and 13% in term boys (P<.01). Weight velocity, but not height velocity, was higher in post-term boys at age 1.5-7 years (P<.05) and again at age 11.5-16 years (P<.05). BMI was higher in post-term boys at age 3 years, with the difference increasing thereafter. BMI and growth were similar in post-term and term girls.

Conclusion: In this post-term birth cohort, boys, but not girls, demonstrated accelerated weight gain during childhood, leading to greater risk of obesity in adolescence.