Background Recent data suggest that children of mothers who are obese before pregnancy, or who gain too much weight during pregnancy, may be at an increased risk of cognitive impairments.

Methods Mother–infant dyads enrolled in a birth cohort study in Pittsburgh, Pennsylvania (1983–1986), were followed from early pregnancy to 14 years postpartum (n=574). Math, reading and spelling achievements were assessed at ages 6 and 10 years using the Wide Range Achievement Test-Revised, and at age 14 years using the Wechsler Individual Achievement Test Screener. Self-reported total GWG was converted to gestational age-standardised z-scores. Generalised estimating equations were used to estimate the effects of GWG and pre-pregnancy body mass index (BMI) on academic achievement at 6, 10 and 14 years, while adjusting for maternal race, child sex, parity, employment, family income, maternal intelligence, maternal depression, pre-pregnancy BMI (in GWG models only) and the home environment.

Results The mean (SD) BMI was 23.4 (5.7) kg/m² and the mean (SD) GWG reported at delivery was 14.4 (5.9) kg. There was a significant non-linear association between pre-pregnancy BMI and an offspring's academic achievement. At 6, 10 and 14 years, an offspring's academic scores were inversely associated with pre-pregnancy BMI beyond 22 kg/m². High GWG (>1 SD) was associated with approximately 4-point lower reading (adjusted β (adjβ) −3.75, 95% CI −7.1 to −0.4) and spelling scores (adjβ −3.90, 95% CI −7.8 to −0.2), compared with GWG −1 to +1 SD.

Conclusions Future studies in larger and socioeconomically diverse populations are needed to confirm maternal weight and weight gain as causal determinants of a child's academic skills, and whether this effect persists into adulthood.