Pre-pregnancy BMI more strongly linked to risk than weight gain

Author: Louise Prime

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Women’s pre-pregnancy body mass index (BMI) was associated more strongly than gestational weight gain with the risk of adverse maternal and infant outcomes, in a new meta-analysis* published in JAMA. But the study authors pointed out that although the estimates of optimal gestational weight gain might inform prenatal counselling, the optimal gestational weight gain ranges had only limited predictive value for the outcomes assessed.

The research team pointed out that gestational weight gain – which reflects several factors including maternal fat accumulation, fluid expansion, and the growth of the foetus, placenta, and uterus – has previously been found to be related to the risk of pregnancy complications, maternal postpartum weight retention, and obesity in offspring. Some gain is necessary to ensure a healthy foetus, but excessive gestational weight gain has been associated with adverse outcomes.

They pooled individual participant data from 25 pregnancy and birth cohorts (with a total of 196,670 participants) from Europe and North America to calculate associations of the amount of gestational weight gain with maternal and infant outcomes according to baseline weight status of underweight, normal weight, overweight, obesity grade 1, obesity grade 2, and obesity grade 3. They grouped maternal pre-pregnancy BMI into categories by two BMI units, and clinical BMI groups according to World Health Organization definitions; and grouped gestational weight gain into categories of 2kg each, ranging from weight loss to weight gain of 28kg or greater.

The study authors defined adverse outcomes as at least one of preeclampsia, gestational hypertension, gestational diabetes, caesarean delivery, preterm birth, and small or large size for gestational age at birth. They reported that overall, any adverse outcome occurred in 37.2% (n = 73,161) of women, ranging from 34.7% (2,706 of 7,809) among women categorised as underweight to 61.1% (592 of 969) among women categorised as obesity grade 3.

They also calculated that the gestational weight gain ranges associated with the lowest risks for any adverse outcomes were 14.0kg to <16.0kg for women categorised as being underweight before pregnancy; 10.0kg to <18.0kg for normal pre-pregnancy weight; 2.0kg to <16.0kg for overweight; 2.0kg to <6.0kg for obesity grade 1; weight loss, or gain of 0kg to <4.0kg for obesity grade 2; and weight gain of 0kg to <6.0kg for obesity grade 3.

They commented: “

Gestational weight gain outside these ranges was associated with adverse outcomes. However, discriminative performance of gestational weight gain with adverse maternal and infant outcomes was low to moderate. Pre-pregnancy BMI was more strongly associated with adverse maternal and infant outcomes than the amount of gestational weight gain.”

The researchers said their results suggest that pre-pregnancy weight might be a more important target for interventions than gestational weight gain. They added that based on current evidence, future clinical trials designed to reduce weight-related maternal and infant adverse outcomes should focus on maternal weight before or at the start of pregnancy.

They concluded: “The estimates of optimal gestational weight gain may inform prenatal counselling; however, the optimal gestational weight gain ranges had limited predictive value for the outcomes assessed.”


* LifeCycle Project-Maternal Obesity and Childhood Outcomes Study Group. Association of gestational weight gain with adverse maternal and infant outcomes. JAMA 2019; 321(17): 1702–1715. doi:10.1001/jama.2019.3820

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