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Obesity Before Pregnancy Linked To Earliest Preterm Births, Study Finds

Posted:  Friday, July 04, 2014

Obesity may lead to long-term health problems like high cholesterol, type 2 diabetes, and stroke. But add pregnancy into the equation, and some of these risks are augmented for both mother and child.

Women who are obese before they become pregnant face an increased risk of delivering a very premature baby, according to a new study of nearly 1 million California births. The findings from the Stanford University School of Medicine provide important clues as to what triggers extremely preterm births, specifically those that occur prior to 28 weeks of pregnancy.

The study, published in the July issue of Paediatric and Perinatal Epidemiology, found no link between maternal obesity and premature births that happen between 28 and 37 weeks of the normal 40-week gestation period. The disparity suggests that premature birth may have different causes at different stages of pregnancy.

"Until now, people have been thinking about preterm birth as one condition, simply by defining it as any birth that happens at least three weeks early," said Gary Shaw, professor of paediatrics and lead author of the new study. "But it's not as simple as that. Preterm birth is not one construct; gestational age matters."

Preterm births affect one in nine pregnancies, or more than a half-million U.S. babies per year. Prematurity can lead to lifelong health problems, such as cerebral palsy, developmental delays and impaired vision or hearing. Babies born before 28 weeks of pregnancy are at especially high risk.

High U.S. prematurity rates prompted the 2011 launch of the March of Dimes Prematurity Research Centre at Stanford University School of Medicine, the first of five such centres the March of Dimes has planned across the country. The new findings are a product of the centre’s work.

For first-time mothers, obesity was linked with a substantial increase in risk of delivery before 28 weeks of pregnancy. The risk was highest at the earliest gestational ages and also at the highest levels of obesity. For instance, non-Hispanic, white first-time mothers in the most obese category were six times more likely than normal-weight women to deliver a baby between 20 and 23 weeks.

Obese women having their second or later child were also more likely to deliver very early than normal-weight women, though the risk was less pronounced than for first-time mothers.

"Ideally, as the American College of Obstetricians and Gynaecologists has already recommended, women should embark upon a healthy diet and exercise program before becoming pregnant," said study co-author Deirdre Lyell, MD, associate professor of obstetrics and gynaecology and an obstetrician at Lucile Packard Children's Hospital Stanford.

A number of factors can contribute to obesity, but the same common-sense diet and fitness recommendations apply to all women, regardless of their pregnancy status. Being in contact with a prenatal physician, sticking to a balanced diet, and exercising regularly can make all the difference in the wellness of a mother and her child.

Research also shows that genetic changes leading to obesity can be passed down from an obese mother to her child, but maternal weight loss surgery before pregnancy can help reduce these risks.