About 1 in 4 women now are obese at the time they become pregnant.
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Pregnant women who eat a diet rich in vegetables, fruits and whole grains and drink plenty of water may have a lower risk of giving birth before their pregnancy reaches full term, a large new study from Norway suggests.
Preterm delivery, defined as giving birth between 22 and 37 weeks of pregnancy, is linked with short- and long-term health problems in children, and accounts for nearly 75 percent of all newborn deaths, according to the study.
Pregnant women in the new study who ate either a diet of fruits, veggies and whole grains, or a diet of boiled potatoes and fish were less likely to have a preterm birth compared with women whose diets included salty and sweet snacks, and processed meat, researchers reported today (March 4) in the journal BMJ.
But the findings don't establish a causal link between diet and preterm birth, the researchers said.
"We don't completely understand preterm labor, and nutrition is only one factor," said Christine Metz, an obstetrics researcher at The Feinstein Institute for Medical Research in Manhasset, N.Y., who was not involved in the study.
The biggest risk factor for preterm labor is having a previous preterm birth, though factors such as smoking, alcohol or drug use, inadequate prenatal care or having twins or triplets also play a role, Metz told Live Science. [Blossoming Body: 8 Odd Changes That Happen During Pregnancy]
The new study was based on data from the Norwegian Mother and Child Cohort Study, which includes 66,000 Norwegian women who gave birth between 2002 and 2008. The women completed a questionnaire about their dietary habits during the first four to five months of pregnancy. Women who had diabetes, and those who did not deliver a single, live baby were excluded from the study.
The researchers classified the women's diets as "prudent," "traditional" or "Western." A prudent diet consisted of raw and cooked vegetables, salad, fruit and berries, nuts, vegetable oils, whole grain cereals, poultry and water to drink. "OB/GYNs are always going to recommend a prudent diet," Metz said.
A "traditional" diet, by contrast, was mainly composed of boiled potatoes, fish, gravy, margarine, rice pudding, low-fat milk and cooked vegetables.
Lastly, a "Western" diet contained a lot of salty snacks, chocolate and sweets, cakes, French fries, white bread, ketchup, sugar sweetened drinks, processed meat products, and pasta.
Preterm births occurred in 3,505 women, or 5.3 percent of those in the study. Eating the prudent diet was linked to a lower risk of preterm birth, especially for women who were having their first baby, the analysis showed. Eating the traditional diet was also linked to a lower risk of preterm delivery compared with the Western diet, but to a lesser extent than the prudent diet.
It may be more important for pregnant women to consume more healthy foods than it is to cut out junk food or processed food, the researchers said.
The findings reinforce existing nutrition guidelines for pregnant women, but they don't establish a causal relationship between diet and preterm delivery, said Dr. Shilpi Mehta-Lee, an OB/GYN at NYU Langone Medical Center who was not part of the research.
However the study "opens the question" of whether there should be trials testing diet changes in pregnant women, Mehta-Lee told Live Science.
It's not clear whether the findings apply to other populations, the researchers noted. The preterm birth rate in the United States is 12 percent, compared with 6 percent of pregnancies in Nordic countries.
Diet can increase the risk of conditions such as gestational diabetes, obesity, preeclampsia (high blood pressure during pregnancy), which in turn might affect the health of the mother or fetus, Metz said. Eating a healthy diet could also benefit the mother long before or after pregnancy, too.
"Pregnancy is one of those teachable moments in a woman's life where she could implement a better diet," Metz said.