Associations of age at first birth and lifetime parity with weight and adiposity across midlife in women from Project Viva

Abstract

ObjectiveThis study aimed to evaluate the associations of age at first birth and parity with weight, waist circumference (WC), and body fat across midlife.MethodsA secondary data analysis was conducted with 735 participants from Project Viva who reported their age at first birth and lifetime parity at a midlife study visit. Weight, WC, and body fat were measured up to four times after the participants' final birth, and associations were examined using linear mixed‐effects regression models.ResultsParticipants' mean (SD) age was 32.6 (4.9) years at enrollment and 30.4 (5.5) years at their first birth, and they had 2.4 (0.9) lifetime births. In adjusted models, women who had their first birth at age <23 or ≥40 years, versus age 30 to 34 years, had a higher trajectory of weight, WC, and body fat after their final birth (i.e., mean differences in weight 8.38 kg [95% CI: 4.13–12.63] for age <23 years and 6.54 kg [95% CI: 0.64–12.45] for age ≥40 years). Women with four or more births, versus two, had a higher trajectory of adiposity after accounting for covariates.ConclusionsWomen who have a first birth before age 23 years or after age 40 years and those with multiple births may benefit from more intensive monitoring for excess adiposity gain.