How Mom’s Weight Before Pregnancy Can Affect a Baby’s Brain

Even before conception, a mother's obesity may affect cognitive development in her baby-to-be.

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A mother’s health during pregnancy has measurable effects on her baby’s well-being, but a new study shows that her fitness before pregnancy matters too. Researchers say that cognitive deficits found in premature babies can be traced to a number of mom-related factors, and one of them is a woman’s pre-pregnancy weight.

The new study, published in the journal Pediatrics, involved 921 preterm infants born before 28 weeks gestation and at lower-than-normal birth weight. About 11% of the babies showed cognitive problems at age 2. Among the infants, the researchers found, those whose mothers were obese (with a body mass index, or BMI, over 30) before they became pregnant had double the risk of developing these cognitive issues.

“What parents need to know is that when it comes to a baby’s brain development, everything is important — even factors prior to getting pregnant. And any changes that they can make toward a healthier lifestyle might improve the outcomes for their babies,” says the study’s lead author Dr. Jennifer Helderman, an assistant professor of pediatrics at Wake Forest Baptist Medical Center.

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The babies and parents participating in the study came from 14 different institutes and agreed to participate in a number of tests to help the researchers determine which factors were most important in influencing brain development. The mothers agreed to give placental biopsies immediately after giving birth, and the babies participated in neurological evaluations and developmental assessments around age 2.

The placental samples helped scientists to determine whether any blockages in the blood vessels feeding the fetus may have impaired the flow of nutrients and oxygen to the developing fetus, thus inhibiting brain development. Indeed, babies who developed in placental environments with blood clots were at a threefold greater risk of lower cognitive scores, compared with infants whose mothers had fewer placental clots.

But of all the mother-related factors that influenced cognitive development, pre-pregnancy obesity stood out. While it’s not entirely clear how a woman’s weight before conception may impact her baby’s brain, Helderman says the leading theory involves inflammation. Excess weight can keep levels of potentially destructive immune cells high; these are the cells that rush to the site of trauma to clear away debris. Studies show that inflammation can adversely affect the brain, and it’s possible that an expectant mom’s heightened inflammatory response could filter through to her developing baby.

Other factors that Helderman and her team identified included familiar ones such as a mother’s education and race. Previous studies have found, as Helderman’s did, that mothers with less than a high school education and those from racial and ethnic minorities were more likely to have babies with cognitive problems.

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And while the results are sobering, they also contain some hope. “This is a factor that is potentially modifiable,” says Helderman. “We’re not saying that weight loss or that maintaining a healthy weight is easy, but for mothers who are interested in doing everything they can for a healthy pregnancy and a healthy baby, this might be one area they want to target.”

Expectant moms already give up smoking and drinking alcohol while pregnant, so addressing weight issues may become another part of a pre-pregnancy checklist. That’s not to say that all normal weight women have healthy babies without cognitive issues, but such deficits are more common among those born premature, and, as these results show, to moms who are obese. “This is important because almost universally, parents interested in this outcome — brain development in their babies,” says Helderman. “If they want to increase their chances of having healthy children, managing their weight may be one thing they can do.”

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.

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