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The following is a summary of “Reevaluating optimal weight changes across the stages of pregnancy,” published in the March 2025 issue of American Journal of Obstetrics & Gynecology by ABOUKHATER et al. 

The optimal weekly weight change by trimester remains uncertain despite National Academy of Medicine (NAM’s) recommendations for total weight change in later pregnancy.  

Researchers conducted a retrospective study to identify optimal weekly weight change rates by trimester linked to lower adverse pregnancy outcomes (APO) stratified by pre-pregnancy body mass index (BMI) categories.  

They used data from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (2010–2014). Weight change per week was calculated as weight change (kg) divided by the gestational weeks interval. Trimester-specific weight change was analyzed: early pregnancy (early first to second trimester), second trimester (second to third trimester), and third trimester (third trimester to delivery). The primary outcome was a composite of APO, including hypertensive disorders of pregnancy, preterm birth, spontaneous preterm birth, small-for-gestational age (SGA) birth, and stillbirth. Restricted cubic spline functions with 5 knots were used to assess nonlinear associations between weight change and APO. Adjusted relative risks (aRR) with 95% CI were calculated using generalized linear models with Poisson distribution and robust error variance, adjusting for confounders. The aRR of APO was estimated for each weight change per week and optimal weight change was identified and compared with the NAM-recommended pregnancy weight change.  

The results showed that among 8,121 individuals, 4,373 (53.8%) had a normal or underweight BMI, 2,002 (24.7%) had an overweight BMI, and 1,746 (21.5%) had an obese BMI. The lowest adverse risks were linked to weight changes per week of 0.7 kg for normal/underweight, 0.7 kg for overweight, and 0.6 kg for obesity in the first trimester; 0.7 kg for normal/underweight, 0.5 kg for overweight, and 0.5 kg for obesity in the second trimester; and 0.5 kg for normal/underweight, 0.4 kg for overweight, and 0.4 kg for obesity in the third trimester. In the second trimester, weight gain per NAM guidelines vs optimal weight gain was linked to a higher risk of adverse pregnancy outcomes and preterm birth for normal/underweight and a higher risk of SGA birth for normal/underweight and overweight individuals. In the third trimester, weight gain per NAM guidelines vs optimal weight gain was associated with a lower risk of cesarean delivery for individuals with obesity.  

Investigators concluded that the gestational weight change rates associated with the lowest adverse risks were higher than those established by the NAM. 

Source: ajog.org/article/S0002-9378(25)00171-1/abstract