Obesity in Pregnancy: Do Guidelines Recommend Too Much Weight Gain?

Pregnancy weight gain below the current minimum recommended by the U.S. Institute of Medicine (IOM) for obese patients did not appear to increase their risk for maternal and fetal complications and was linked to reduced risk for severely obese patients, a large population-based study from Sweden found.

With a body mass index (BMI) of 30.0 to 39.9, pregnancy weight gains below the 5 kg (11 lb) recommended did not significantly increase risk of a composite of adverse outcomes (adjusted RR 0.97 for obesity class 1 and 0.96 for class 2), reported Kari Johansson, PhD, of the Karolinska Institute in Stockholm, and co-authors.

For women with class 3 obesity (BMI ≥40.0), weight gain below the IOM lower limit or weight loss actually had a reduced risk of the adverse composite outcome (adjusted RR 0.81 at 0 vs 5 kg weight gain, 95% CI 0.71-0.89), the researchers reported in The Lancet.

Ultimately, the authors concluded that less pregnancy weight gain, or even weight loss, was safe for obese patients.

“Our findings support calls to lower or remove the lower limit of current IOM recommendations for pregnant women with obesity, and suggest that separate guidelines for class 3 obesity might be warranted,” they concluded.

The IOM currently recommends individuals with obesity gain between 5 and 9 kg, but Johansson told MedPage Today that there are “concerns that these recommendations are too high and a single recommendation for all individuals with obesity is insufficient.”

Re-evaluating these guidelines “may help to reduce the high burden of poor maternal and infant health outcomes associated with pre-pregnancy obesity,” she noted. For instance, other studies have found that excessive weight gain in pregnancy was tied to earlier death.

This cohort study analyzed singleton pregnancies identified in the Stockholm-Gotland Perinatal Cohort, which prospectively collected birth data via electronic medical records in Sweden from 2008 through 2020. Authors looked at patients who delivered from January 2008 through December 2015, and followed their health data for at least 4 years postpartum (median 7.9 years). They analyzed a composite of 10 outcomes: stillbirth, infant death, large or small for gestational age at birth, preterm birth, unplanned caesarean delivery, gestational diabetes, preeclampsia, excess postpartum weight retention, and new-onset longer-term maternal cardiometabolic disease after pregnancy.

Of the total of 15,760 pregnancies in the cohort with a BMI of at least 30 before 14 weeks’ gestation, average maternal age was about 31. About a third went on to have another pregnancy. Most women (11,667) were in obesity class 1 with a BMI of 30.0-34.9, another 3,160 were in class 2 with a BMI of 35.0-39.9, and 933 were in class 3 obesity. Among these pregnancies, 13.9% of class 1, 24.9% of class 2, and 33.2% of class 3 gained less weight than the lower limit of IOM recommendations.

Gestational weight gain was the last measured weight at or before delivery minus early pregnancy weight before 14 weeks’ gestation. Patients with no antenatal weight gain measurements were excluded, as were those with missing or implausible BMIs during early pregnancy, as well as those with an early pregnancy BMI less than 30.

The team also did four sensitivity analyses: lowering the threshold for excessive postpartum weight retention, different definitions of small and large for gestational age, modeling the composite outcome as a binary yes/no event, and repeated analyses for a cohort only including individuals with complete data on outcomes. Findings were similar in these analyses.

Johansson suggested that future research examine overweight, normal weight, and underweight women in a similar way.

The researchers noted limitations including use of proxies for certain measures within the composite outcome and not having data on diet or physical activity. Additionally, Swedish law prohibits registration of race or ethnicity on Swedish registers.

“Of note, the gender distribution in our cohort is unknown, and if the effect of pregnancy weight gain on adverse health outcomes differs in transgender women, our findings might not be generalizable to these individuals,” they added.

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