More pregnancy weight gain, more maternal risk?

Clinical takeaway: Counsel pregnant patients to stay within recommended gestational weight-gain ranges whenever possible. Excessive weight gain was associated with a 16%-33% higher risk of severe maternal morbidity across all prepregnancy BMI categories, while inadequate gain was also associated with elevated risk in patients with normal weight or overweight.

Current gestational weight-gain recommendations were developed largely around infant outcomes such as birth weight and preterm birth, not maternal safety. Severe maternal morbidity, which includes complications such as severe hemorrhage, preeclampsia/eclampsia, ICU admission, and hysterectomy, continues to rise and represents a major public health concern.

Excessive gestational weight gain was common in this population-based cohort study of 1,035,927 singleton pregnancies in Ontario, Canada. More than half of pregnant individuals (52.8%) gained more weight than recommended, while 18.6% gained less than recommended. Overall, 15,119 severe maternal morbidity (SMM) events occurred, corresponding to about 14.6 cases per 1,000 births.

Compared with patients whose weight gain fell within Institute of Medicine recommendations, those with excessive weight gain experienced consistently higher SMM risk regardless of starting BMI. Relative increases ranged from 16% among patients with overweight to 33% among those with underweight; risk increases were also observed across all obesity classes, ranging from about 21% to 28%.

Patients with inadequate weight gain were not spared. SMM risk was 13% higher among those with normal weight and 19% higher among those with overweight at baseline.

Preexisting conditions including diabetes, hypertension, cardiovascular disease, asthma, and pulmonary disease roughly doubled SMM risk. When these comorbidities occurred alongside weight gain outside recommended ranges, risk was even greater, identifying a subgroup that may warrant closer surveillance.

The most common SMM events were severe hemorrhage and severe preeclampsia/eclampsia/HELLP syndrome. Notably, the association between excessive weight gain and SMM appeared to be driven in part by hypertensive complications.

"Our findings provide important evidence for clinicians and policymakers," senior author Laura Anderson said in a statement. "More than half of pregnancies in our study involved weight gain above current recommendations, underscoring how challenging healthy weight gain during pregnancy can be."

Source: Khademioore S, et al. (2026 Oct 22) JAMA Network Open. Weight Gain During Pregnancy and Severe Maternal Morbidity