Impact of maternal body mass index (<scp>BMI</scp>) and gestational weight gain on offspring's weight and <scp>BMI</scp><i>z</i>‐scores across the first 8 years of life

While prior studies have linked maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) to birth weight and early childhood obesity, fewer have examined their joint effect on longitudinal growth trajectories, particularly standardized BMI z-scores through school age. We aimed to examine the relationship between maternal pre-pregnancy BMI, GWG and the trajectory of offspring's early-life weight, BMI z-scores and weight percentiles from birth to age 8. Linear mixed models were employed to assess the association between maternal pre-pregnancy BMI, GWG and children's standardized weight-for-age, BMI and length/height-for-age, adjusting for potential confounders. Data were analysed from 806 mother-child pairs from the Vitamin D Antenatal Asthma Reduction Trial, with children followed longitudinally from birth through 8 years of age. Our study demonstrated a significant association between maternal pre-pregnancy BMI and offspring weight-for-age and BMI z-score trajectories (β = .03, 95% confidence interval [CI]: 0.02-0.04 for both; p < .001, respectively). Specifically, children born to mothers with pre-pregnancy BMI of 25-30 kg/m² or ≥30 kg/m² had significantly higher BMI z-scores (β = .15, 95% CI: 0.02-0.29; p = .03; β = .49, 95% CI: 0.33-0.64; p < .001, respectively) compared to those with normal BMI. Maternal BMI was not significantly associated with the child's length/height. GWG was independently and positively associated with weight-for-age and BMI z-scores (β = .01, 95% CI: 0.002-0.015, p = .01 and β = .01, 95% CI: 0.01-0.02, p < .001, respectively). Excessive GWG was linked to higher offspring weight-for-age and BMI z-scores from birth to 8 years (β = .20, 95% CI: 0.08-0.32; β = .19, 95% CI: 0.08-0.31; p = .001, respectively) compared to guideline-congruent or inadequate GWG. Achieving or maintaining a healthy BMI prior to pregnancy and adhering to GWG guidelines may help mitigate the risk of early childhood overweight or obesity.