Scientists Studied 1 Million Pregnancies, Then Found One Overlooked Risk

Scientists studied over one million pregnancies and discovered an overlooked risk linked to excessive weight gain during gestation. The research, conducted by a team led by Laura Anderson, an associate professor at McMaster University’s Department of Health Research Methods in Ontario, Canada, revealed that gaining too much weight during pregnancy significantly increases the likelihood of experiencing severe maternal morbidity (SMM). SMM encompasses life-threatening complications such as major hemorrhage and sepsis, which can have lasting effects on a mother’s health. The study found that the heightened risk of these complications ranged from 16 percent to 33 percent, affecting all body mass index (BMI) categories, including women who were underweight, at a healthy weight, overweight, or obese. The analysis covered data from April 2012 through March 2022, drawing on population birth registry information and hospitalization records in Ontario. It included 1,035,927 singleton pregnancies delivered in hospitals. According to the findings, 52.8 percent of women gained more weight than recommended, 28.6 percent gained an appropriate amount, and 18.6 percent gained less than advised. Approximately 1.46 percent of women, around three in every 200 pregnancies, developed severe maternal morbidity. Among those who gained excessive weight, the risk of SMM varied depending on their pre-pregnancy BMI. Women who were underweight before pregnancy faced a 33 percent higher risk compared to those who gained the recommended amount of weight. Normal-weight women saw a 24 percent increase, while overweight individuals experienced a 16 percent rise. Obesity categories showed similar patterns, with Class II and Class III obesity showing elevated risks. The study also highlighted how existing health conditions could exacerbate the dangers of excessive weight gain. Pre-pregnancy medical issues such as diabetes and hypertension were found to heighten the risk of SMM. For instance, a woman who entered pregnancy at a normal weight but had chronic hypertension or diabetes and gained excessive weight faced nearly three times the risk of severe maternal morbidity compared to a normal-weight woman without preexisting conditions who gained the recommended amount of weight. Additionally, insufficient weight gain was linked to increased risk in certain groups, especially those who began pregnancy at a normal weight or were overweight. The researchers emphasized that maintaining a healthy weight gain during pregnancy is crucial for all women, regardless of their initial BMI. “Healthy pregnancy weight gain isn’t just important for women with a higher BMI; it matters for all pregnant women whatever their weight,” said Sahar Khademioore, a Ph.D. candidate in the Health Research Methodology Program. She noted that excessive weight gain was widespread and increased the risk of serious complications across all BMI categories. This underscores the importance of providing more support for healthy weight management during pregnancy to improve outcomes for both mothers and infants. The study relied on data collected from hospitalization records and birth registries, offering a comprehensive view of pregnancy-related health outcomes. Researchers used the Institute of Medicine (IOM) guidelines to determine the recommended weight gain based on pre-pregnancy BMI. These recommendations range from 28–40 pounds for underweight women to 11–20 pounds for those with obesity. The findings suggest that even women who start pregnancy at a healthy weight must be mindful of their weight gain to avoid potential complications. Further research will likely explore the mechanisms behind these associations and how they might vary across different populations. Until then, healthcare providers may consider revising prenatal care strategies to better address the risks associated with both excessive and insufficient weight gain.