Interpregnancy interval, maternal age, and offspring's BMI and blood pressure at 7 years of age.

Interpregnancy interval and maternal age are associated with birth outcomes. However, it is unknown regarding their long-term effects on child health. We aim to assess the associations between interpregnancy interval and offspring's body mass index (BMI) and blood pressure (BP) at age of 7 years and to examine the role of maternal age in the associations. A secondary analysis was performed among 2604 mother-infant pairs in the prospective National Collaborative Perinatal Project, in which the children were followed up until 7 yrs of age. Interpregnancy interval was positively associated with offspring's diastolic BP at 7 yrs (β = 0.053, 95% CI: 0.004-0.102) after adjusting for maternal and perinatal characteristics, feeding pattern, rapid weight gain in the first year of life, and current BMI z score and height z score. The inclusion of maternal age in the model did not change the effect size. Maternal age was independently associated with offspring's BMI z score at 7 yrs (β = 0.014, 95% CI: 0.001-0.027). An interaction between interpregnancy interval and maternal age was present in the association with diastolic BP (P = 0.019), and the increasing maternal age aggravated the effects of long interpregnancy interval. Our finding suggests long interpregnancy interval is a risk factor for higher diastolic BP of the offspring. Increasing maternal age could amplify the impact. Our study challenges the current WHO recommendation for ideal interpregnancy interval, and we would suggest lowering the recommendation to <24 months and even shorter for women of advanced age.