Babies who are born to obese or overweight women are more likely to experience an oxygen deficit at birth than babies born to average-weight women, a new study suggests.
In the study, researchers found that a baby's risk of having a low Apgar score — a measure of oxygen deficit at birth — increased with maternal body mass index (BMI). Babies born to overweight women (with a BMI of 25 to 29.9) had a 55 percent increase in the risk of low Apgar scores at five minutes after birth, compared with babies born to normal-weight women. Babies born to obese mothers (with a BMI of 30 to 39.9) had a twofold increase in risk, and infants born to very obese women (with a BMI of 40 or higher) had a more than threefold increase in risk.
"Our results add to previous knowledge that maternal overweight and obesity increase risks for maternal, fetal and neonatal complications," said study author Dr. Martina Persson, of the Swedish medical university Karolinska Institutet.
"Women who want to get pregnant should strive towards normal body weight before conception," Persson told Live Science. [7 Ways Pregnant Women Affect Babies]
The researchers examined data from the Swedish medical birth registry for all 1.7 million births that occurred in the country between 1992 and 2010. A baby's Apgar score is a quick test that rates his or her health on a scale of zero to 10, taking into account the baby's breathing effort and heart rate, among other factors. The researchers considered an Apgar score of 3 or below low enough to indicate an oxygen deficit at birth, also known as birth asphyxia.
Birth asphyxia can sometimes result in seizures or meconium aspiration, a condition in which a baby's stool gets into the lungs, Persson said.
Previous research has shown a link between a pregnant woman's obesity and other delivery complications, as well as an increased risk of fetal and infant mortality.
Even though the new study linked a mother's BMI with an increased risk of asphyxia for the baby, it is important to note that the overall risk of asphyxia in babies born to mothers with normal weight is very low, Persson said.
The study found that for babies born to mothers with the most severe form of obesity (a BMI of 40 or higher), the rate of birth asphyxia was 2.4 per 1,000 births, compared with 0.6 per 1,000 among babies born to women of normal weight, she said.
So, what can women do to reduce the chances of having a baby with birth asphyxia?
"I would encourage all pregnant women, irrespective of BMI, to try to enjoy their pregnancy, and to try to eat healthy and to be physically active," Persson said.
"In our analyses, we found that mode of delivery [whether a baby was delivered vaginally, or by Cesarean section] did not substantially affect the risks of birth asphyxia in offspring of overweight and obese women," Persson added. "However, it is very likely that close fetal monitoring and active management during labor and delivery could reduce risks for birth asphyxia and related outcomes."
The researchers are not sure exactly how a woman's BMI may influence her baby's risk of birth asphyxia. One possible explanation is that maternal obesity comes with certain metabolic changes and a state of inflammation that may increase insulin production in the fetus before the baby's birth, Persson said, and this may, in turn, cause the fetus to get significantly larger.
"High levels of fetal insulin will accelerate fetal growth," Persson said. "Large babies more often experience traumatic deliveries — a risk factor for birth asphyxia."
The study was published today (May 20) in the journal PLOS Medicine.