Even before babies are born, their immune systems can be significantly affected by their mother’s weight during pregnancy, researchers have found. Later in life, these weakened protection systems can put children at risk of diseases including heart disease and asthma, making the issue of overweight mothers not just a personal matter but one of public health proportions.

Researchers at the University of California, Riverside looked at umbilical cord blood samples from 39 mothers in Portland, Oregon. Eleven were slim, 14 overweight and 14 obese. All had uncomplicated pregnancies and births. Hailing from a variety of racial and ethnic backgrounds, they didn’t smoke, and they didn’t have diabetes.

But babies whose mothers had high body mass indexes (BMI) -- a ratio that compares weight and height so that if those who have a higher BMI are more overweight -- lacked specific cells that help immune systems fight off infections, the research team’s analysis showed. They also had fewer cells that affect allergic responses and asthma, a reduction that might explain why children born to obese mothers tend more often to develop asthma later on in life.

“Our study offers potential links between changes in the offspring’s immune system and the increased susceptibility and incidence of these diseases later in life,” namely heart disease and asthma, Ilhem Messaoudi, an associate professor of biomedical sciences who led the research team, said in a press release. The study is scheduled to be published in the journal Pediatric Allergy and Immunology.

Messaoudi added that along with smoking, drug use and alcohol, a mother’s weight needed to be factored into the conversation between doctors and women who were planning to have children. “Obesity has serious repercussions for maternal health,” she added, pointing out that obesity can affect a woman’s ability to become pregnant and lead to complications during the pregnancy itself.

In the United States, nearly 60 percent of women who are of childbearing age (typically between 15 and 44 years) are overweight or obese, according to the press release. Other estimates state that 20 percent of women in the United States are obese when they conceive a child, and that the percentage of childbearing who are overweight is expected only to increase in the future.

Fathers too, however, bear responsibility when it comes to weight and their children’s health. At least one medical study has shown that children of fathers who were obese at the time of the child’s conception are at greater risk of inheriting certain factors that can spur obesity and related health problems, such as diabetes.