Pregnancy complications such as preeclampsia and gestational diabetes have recently been associated with a higher risk of developing heart disease later in life. But a new Northwestern Medicine study has found obesity before or during pregnancy is the actual root cause of future cardiovascular disease.

Prior to this study, scientists were unsure which factor — obesity or pregnancy complications — played a larger role in cardiovascular disease risk years after pregnancy. This large, multi-center and diverse study is the first to disentangle that question, ultimately determining that pre-pregnancy obesity is the true driver of both poor pregnancy outcomes and future cardiovascular disease risk. It is one of the only studies to follow its participants — about half of whom were overweight or had obesity — from the beginning of their first pregnancy through several years postpartum.

“We demonstrate, for the first time, that adverse pregnancy outcomes are primarily indicators — and not the root cause — of future heart health,” said corresponding author Dr. Sadiya Khan, the Magerstadt Professor of Cardiovascular Epidemiology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician. “This means that pregnancy just reveals the risk for heart disease that is already there.”

The findings were published Oct. 10 in the journal Circulation Research.

The study used data from the nuMoM2b Heart Health Study to prospectively follow 4,216 first-time pregnant individuals from the early stages of their pregnancy to an average of 3.7 years postpartum. At the early-pregnancy first study visit, the average maternal age was 27 years old, and 53% had a normal body mass index (BMI), 25% were overweight and 22% had obesity. Compared to those with a normal BMI in early pregnancy, individuals with overweight or obese BMI had a higher risk of developing hypertensive disorders of pregnancy.

‘Pregnancy is a natural stress test for the heart’

In the study, the scientists wanted to better understand the associations among maternal obesity, hypertensive disorders of pregnancy and other adverse pregnancy outcomes, and cardiovascular health several years after delivery.

“Our hypothesis was that it may be that the pregnancy complications are unmasking these things since, as we know, pregnancy is a natural stress test for the heart,” Khan said. “These findings are important because if pre-pregnancy obesity is the culprit or cause of risk, we should be targeting this with interventions.

“We don’t want to just wait until people have these cardiovascular events; we want to stop them from happening,” Khan said.

Obesity intervention before pregnancy is key

A major throughline of Khan’s research is the idea of the “Zero trimester,” or pre-pregnancy health. By improving health during this critical time in an individual’s life, they can improve outcomes for not only their pregnancy and baby but for their personal long-term health, Khan said.

However, it can be difficult to target people before becoming pregnant, Khan said. So, early in the pregnancy may be an opportune time to counsel on heart-healthy habits like diet and exercise when people are more likely to be interacting with clinicians during prenatal visits.

“We definitely do not want to recommend weight loss during pregnancy but do want to recommend counseling and monitoring for appropriate gestational weight gain,” Khan said. “It is one of the few times in life that you are seeing the doctor frequently while you’re healthy.”

Pregnant individuals can safely limit their weight gain throughout pregnancy by eating healthy and exercising moderately or even vigorously, studies have shown.