Context: Evidence suggests that babies' fat mass at birth is greater if their mothers were themselves fatter during pregnancy, but it is unclear whether this association persists into childhood.

Objective: To examine the relation between maternal size in pregnancy, early growth and body composition in children.

Design: Prospective cohort study

Setting: Southampton, UK.

Participants: 216 nine-year-old children whose mothers had participated in a study of nutrition during pregnancy.

Main outcome measures: Fat mass and lean mass measured by dual-energy X-ray absorptiometry, adjusted for height ("fat mass index" and "lean mass index").

Results: Fat mass index at age nine years was greater in children whose mothers had a larger mid-upper arm circumference in late pregnancy or a higher pre-pregnant body mass index. For one standard deviation (SD) increase in maternal mid-upper arm circumference in late pregnancy, fat mass index rose by 0.26 (95% CI 0.06–0.46) SD in boys and by 0.44 (95% CI 0.31–0.57) SD in girls. For one SD increase in maternal pre-pregnant BMI, fat mass index rose by 0.26 (95% CI 0.04–0.48) SD in boys and by 0.42 (95% CI 0.29–0.56) SD in girls.

Conclusions: Mothers with a higher pre-pregnant body mass index or a larger mid-upper arm circumference during pregnancy tend to have children with greater adiposity at age nine. The extent to which this is attributable to genetic factors, the influence of maternal lifestyle on that of her child, or maternal adiposity acting specifically during pregnancy on the child's fat mass cannot be determined in this study.