Pregnant women who are obese or overweight are at a higher risk of giving birth prematurely, according to a new study published in the Journal of the American Medical Association.

The Swedish study, led by Dr. Sven Cnattingius of the Karolinska Institute in Stockholm, included an analysis of over 1.5 million births.

This isn’t the first study that’s looked at the link between being overweight during pregnancy and risk of premature birth. Researchers at McMaster University revealed that overweight and obese women are at a 30 percent increased risk of induced preterm births and that their children may suffer serious health consequences from early birth.

In this study, researchers investigated whether being overweight or obese has any significant impact on pregnancy, increasing the risk of premature birth.

Premature birth is when the baby is born at less than 37 weeks of gestation. It is one of the main causes of neonatal illness and infant mortality.

A total of 1.59 million births between 1992 and 2010 were analyzed from the Swedish Medical Birth Register, the investigators checked the mother’s body-mass-index as well as any pregnancy complications, or health risks after birth.

Dr. Raul Artal, professor and chairman of the department of obstetrics at the Saint Louis University School of Medicine, who wasn’t involved in the study, said the findings of this study “reinforces the fact that the complications of obesity and additional weight gain are deleterious to both mother and fetus.”

Obese women who are pregnant could prevent health complications for their child by losing a bit of weight, a concept which was previously considered to be avoided. The American Congress of Obstetricians and Gynecologists have issued a statement saying that it’s OK for pregnant women who are obese to lose weight.

The researchers found that among the pregnant women, the higher their BMI, the higher their risk of premature birth.

The U.S. has preterm delivery rates that are more than double Sweden’s, and the percentage of pregnant women in the U.S who are considered to be overweight or obese is substantially higher than in Sweden.

Extremely pre-term births are one of the main causes of long-term disability and account for a quarter of infant deaths in the U.S.

Previous studies have found that women who have a spontaneous preterm delivery have high levels of cytokines in their body – inflammatory proteins – linked to neonatal health complications. Obese women are more likely to experience inflammation which increases their risk of urinary tract and vaginal infections, which in turn raise the risk of preterm birth.

A study from the Centers for Disease Control and Prevention (CDC) and Kaiser Permanente Northwest Center for Health Research, published in the New England Journal of Medicine, found that obesity during pregnancy is associated with greater use of health care services and longer hospital stays.

According to previous research published in the BMJ, obese women who undergo bariatric surgery before having a baby are at a reduced risk of experiencing severe health problems during pregnancy.

Overweight and obese women at raised risk of adverse neonatal and maternal outcomes

Written by Joseph Nordqvist