Pregnant Moms' Weight Affects Babies' Health

New research shows that how much you weigh before pregnancy—as well as how much weight you gain during it—is linked to rates of infant mortality.

Pregnant Moms' Weight Affects Babies' Health Donato Sardella/Getty Images

Kim Kardashian famously opened up about gaining at least 52 pounds during her second pregnancy, nearly 20 pounds more than what's recommended. Although this happens to moms-to-be all the time, a new study to be published in the journal Obesity shows that when you're pregnant, it's not only yourself you should be worried about, because an unhealthy weight in expectant moms is directly linked to their babies' health—including their risk of death.

Researchers at the University of Pittsburgh's Graduate School of Public Health looked at data from more than 1.2 million births in Pennsylvania, including 5,530 infant deaths that occurred before the child's first birthday. "We found that weight gains that were very far below the current guidelines and weight gains above these guidelines were associated with an increased risk of infant death," Lisa M. Bodnar, Ph.D., M.P.H., R.D., an associate professor in the departments of Epidemiology and Obstetrics & Gynecology, tells Fit Pregnancy. The farther from normal weight in either direction, the greater the danger to baby—with the magnitude of the risk approaching that of smoking.

Why does mom's weight impact baby?

While weight gain during pregnancy is critical for infant health, so is mom's weight before pregnancy. In fact, Bodnar says, "even when women who were obese gained an optimal amount of weight, their risk of infant death was still much higher than normal weight women." The study notes that babies whose moms start out pregnancy with obesity have a 40 percent greater chance of death than moms who start out with a normal weight.

The connection between maternal weight and infant health is not fully understood, but it could have something to do with consequences of poor birth outcomes among babies of moms who were not of optimal weight before or during pregnancy. "We assume from our data that obese mothers have babies that are more often born extremely early, and this prematurity threatens survival," she says. "We also believe that obese mothers who deliver infants at term are also at risk of death through events that occur during labor and delivery that may impair oxygen delivery to the baby." In addition, Bodnar says, babies of obese moms are at risk for obesity in infancy and childhood, and impairments in cognitive function and behavior.

Maintaining a healthy weight

If you're planning to get pregnant, Bodnar says it's a good idea to make sure your body is in the normal body mass index (BMI) range of 18.5-24.9, or around 112 to 149 pounds if you're an average height of 5'5". "I recommend that women who plan to conceive make an appointment with an obstetrician to speak about the benefits of weight loss before pregnancy [or weight gain if you're under the recommended BMI] and how to best achieve this," she says. For weight loss, take a look at your exercise and diet, and start with the most obvious fixes. "Eliminating sugar-sweetened beverages like soda and fruit drinks is one simple way of losing weight," Bodnar says.

But pregnancies aren't always planned, so what if you're already pregnant and not at a healthy weight? Weight loss during pregnancy is definitely not recommended, so just try to be as healthy as you can now. "Focus on eating plenty of fruits, vegetables, nuts and seeds, and lean meat, poultry and seafood," Bodnar says. "Try to avoid eating foods with too much added sugar, like soda, candy or desserts."

How much weight you should gain during pregnancy depends on how much you weighed when you got pregnant. According to the Institute of Medicine, which Bodnar points to, these are the recommended amounts you should put on based on your pre-pregnancy BMI:

  • If you're underweight (a BMI of less than 18.5), you should gain 28-40 pounds.
  • If you're normal weight (a BMI of 18.5-24.9), you should gain 25-35 pounds.
  • If you're overweight (a BMI of 25-29.9), you should gain 15-25 pounds.
  • If you're obese (a BMI of 30 or more), you should gain 11-20 pounds.