Heavier Pregnant Women Tend to Deliver Prematurely
In large Swedish study, risk rose along with the mother's weight
For example, the United States has preterm delivery rates twice as high as Sweden's. In the United States, slightly more than half of women are either overweight or obese in early pregnancy, and severe obesity is much more common than in Sweden. Extremely preterm births accounted for 25 percent of all U.S. infant deaths among single births, and extremely preterm birth is also the leading cause of long-term disability, according to study background information.
The study's results seem to suggest an interplay between health risks linked to overweight and obesity, said Dr. Jill Rabin, chief of ambulatory care, obstetrics and gynecology, and head of urogynecology at Long Island Jewish Medical Center in New Hyde Park, N.Y.
Earlier studies have found that women who suffer a spontaneous preterm delivery have increased levels of inflammatory proteins called cytokines, which are associated with neonatal health problems such as weakening of the membranes and preterm contractions.
Both obesity itself and the health problems that come with obesity increase the amount of inflammation in a woman's body, Rabin said. Obesity and the inflammation that accompanies it also make it more likely that a woman could suffer an intrauterine bacterial infection.
"Obese women have increased risk of urinary tract infections and vaginal infections," Rabin said. "These increase the risk of preterm delivery."
The study noted that a bacterial infection is considered the most important risk factor for spontaneous extremely preterm delivery.
The American Congress of Obstetricians and Gynecologists has issued a recommendation that it is OK for women who are overweight or obese to not gain weight during pregnancy, or even to lose weight, said Artal, of Saint Louis University.
"I consider pregnancy to be an ideal time for behavioral modification," Artal said. He noted that pregnant women have an improved chance to adopt healthy habits because they have better access to medical care than at any other time in their life, are more prone to comply with recommendations because they have the added responsibility of their unborn child, and are under close medical supervision.
Although the study found an association between maternal obesity and premature birth, it did not establish a cause-and-effect relationship.
For his part, Fothergill said the study cries out for follow-up research that will better elaborate upon the link between obesity and premature birth.
"There needs to some additional research that explains why these women are delivering early," he said. "What is it about obesity that's making these women go into labor early?"