Excessive Weight Gain During Pregnancy Linked to Serious Complications in Major New Study

Pregnancy comes with recommended ranges for how much weight to gain, and those ranges were developed mainly with the baby’s health in mind. A new study from McMaster University asks what the same weight gain means for the mother’s health.

Researchers analyzed data on more than 1 million pregnancies in Ontario, Canada, and found that gaining more than the recommended amount was linked to a higher risk of severe complications for the mother.

The results were published Oct. 22 in the journal JAMA Network Open.

That isn’t the whole picture, though. The study also found a risk at the opposite end of the scale, and its senior author says supporting healthy weight gain during pregnancy will take more than counseling individual patients.

Over Half Of Pregnancies Went Past The Recommended Amount

Weight gain above the guidelines was far more common than gain below them.

The study, which drew on the BORN Ontario birth registry, found that 53% of pregnancies involved weight gain above current recommendations. Another 19% fell below them.

Across the whole group, researchers identified more than 15,000 cases of severe maternal morbidity, which McMaster describes as life-threatening complications. Bleeding, pre-eclampsia and ICU admission during childbirth are among the examples.

“We’ve long known that a person’s weight before pregnancy is a risk factor. We wanted to know whether the amount of weight gained during pregnancy also influences the risk of complications,” said lead author Sahar Khademioore, a Health Research Methodology PhD candidate at McMaster.

The researchers found that gaining more than the recommended amount was associated with higher risk in every prepregnancy weight category, based on body mass index (BMI), so the pattern wasn’t limited to people who started pregnancy at one weight. That doesn’t mean the increase was equal across groups, and the size of the increase for each group isn’t given.

Gaining Too Little Showed Up In The Data Too

The findings don’t support gaining as little as possible.

Gaining less than the recommended amount was associated with higher risks of severe maternal outcomes in some BMI groups. The groups aren’t specified.

Existing health conditions also stood out. People with conditions such as diabetes, asthma, and high blood pressure faced roughly double the risk of severe maternal complications. That risk rose further when weight gain also fell outside the recommended range.

McMaster’s announcement stops short of offering a new weight-gain target, a weight-loss recommendation, or a tested intervention, so pregnant readers have no new number to aim for.

Researchers Want Another Look At The Guidelines

Their argument starts with what the recommendations were designed to protect.

Those recommendations were developed around infant outcomes, including healthy birth weight and a lower risk of preterm birth. The McMaster team wants them evaluated against severe maternal outcomes too, though nothing has been announced about changing them. Khademioore said weight gain is something that can potentially be addressed, which makes its link to severe complications a chance to support maternal health better.

Senior author Laura Anderson, an associate professor at McMaster, sees the share of pregnancies above the range as a sign of how challenging healthy gain can be. She said the findings give clinicians and policymakers important evidence. “We also need broader, population-level strategies that create supportive environments for healthy pregnancies,” she added.

Funded by the Juravinski Research Institute, the study is part of the SERENE Project, which aims to understand when and why severe maternal morbidity happens, who is most affected, and the long-term physical, social, and mental health effects.

Related: 15 Ways to Think About Pregnancy That Show Just How Crazy the Human Body Really Is

What The Study Can’t Tell Us Yet

Some of the most useful numbers didn’t make it into McMaster’s announcement.

Absolute risk is missing too: it’s not clear how many extra complications the higher risk adds up to per 1,000 pregnancies.

The weight-gain thresholds used to sort pregnancies, the years covered, and the full definition of severe maternal morbidity aren’t listed either. It’s also unclear what the roughly double risk for people with existing conditions was measured against, or whether other factors were accounted for.

Then there’s timing: did the extra weight come before the complications, and how did the analysis handle that order of events? The announcement doesn’t say, and it doesn’t address how well Ontario results carry over to pregnancies elsewhere.

If you’ve been through a pregnancy, or supported someone who has, what kind of support would have helped most?

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