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Experts say women should focus on achieving a healthy weight before they get pregnant. Getty Images

Women should be more concerned about their weight before they get pregnant than any weight they gain during pregnancy, a new study published today suggests.

That’s because complications during pregnancy are far more likely among women who are overweight or obese than women with a more normal weight who put on extra pounds after they conceive.

The risk of complications, such as preeclampsia, gestational hypertension, gestational diabetes, cesarean delivery, and preterm birth, were highest among women who were both overweight at conception and gained excessive weight during pregnancy.

Researchers from the Netherlands found 34 percent of women with a normal weight experienced pregnancy complications, compared to more than 60 percent of women who were severely obese when they got pregnant.

Moreover, 90 percent of women who started out very obese and had significant additional weight gain during pregnancy experienced complications, according to the study, led by Dr. Romy Gaillard, an assistant professor in the department of pediatrics at the Erasmus MC University Medical Center in Rotterdam.

The study was based on an analysis of data on more than 190,000 mothers and their children in Europe and the United States.

“We were very much surprised by these high percentages of pregnancy complications depending on women’s weight before pregnancy,” Gaillard told Healthline.

“We did observe an association of the amount of weight gain during pregnancy with the risk of pregnancy complications, but this association was much weaker than the association of maternal weight before pregnancy with the risk of pregnancy complications.

“Rather than focusing on maternal weight gain during pregnancy, strategies are needed to optimize maternal weight before the start of pregnancy to improve pregnancy outcomes,” she said.

Many current interventions focus on controlling weight gain from the second half of pregnancy onward. These, Gaillard says, have yielded disappointing results.

About 1 in 4 women in the United States are obese before they become pregnant, according to the Centers for Disease Control and Prevention.

“The study underlines the importance of optimizing maternal BMI (body mass index) before the start of pregnancy,” said Gaillard. “For women who wish to become pregnant, trying to obtain a healthier weight before the start of their pregnancy, instead of only focusing on their weight gain during pregnancy, would be beneficial, as this may reduce their risk of pregnancy complications.”

Dr. Michael Cackovic, obstetric director of the Maternal Cardiac Disease in Pregnancy Program at Ohio State University’s Wexner Medical Center, told Healthline that while the findings “are good for counseling people who we see ahead of time, the problem is that once they are pregnant there’s nothing they can do about it, because we consider losing weight during pregnancy to be unsafe.”

Cackovic says that even women who are morbidly obese — weighing 400 to 600 pounds — aren’t advised to lose more than 10 or 15 pounds once they are pregnant.

Experts say that primary care physicians and gynecologists are in the best position to work with women to achieve a healthy weight before becoming pregnant.

“When I see a woman who is planning to become pregnant, I always recommend she get as close as possible to a normal BMI prior to attempting pregnancy,” Dr. Noelia Zork, a maternal-fetal medicine specialist at New York-Presbyterian/Columbia University’s Irving Medical Center, told Healthline.

“At the first prenatal care visit we discuss her goals for weight gain for that pregnancy based on her prepregnancy BMI. If the woman is planning to get pregnant in the next few months, I recommend she lose 10 to 15 pounds prior to attempting pregnancy,” she said.

“Even a small amount of weight loss can help to improve the outcomes for the pregnancy,” Zork added.

Gestational weight gain, which includes fetal and placental growth, fluid expansion, and maternal fat accumulation, is “necessary to ensure healthy development of the fetus,” the study researchers said.

Too much weight gain during pregnancy can have health consequences, but especially compared to women who were already obese, the “influence of gestational weight gain on these risks seems to be relatively small.”

The Institute of Medicine (IOM) publishes guidelines on optimal weight gain during pregnancy.

Women considered underweight (BMI of 18.5 or less) are advised to gain 28 to 40 pounds.

Those with a normal weight (BMI of 18.5–24.9) are told to gain between 25 and 35 pounds.

Women who are overweight (BMI 25.0–29.9) should gain between 15 and 25 pounds, according to the guidelines, while women who are obese (BMI of 30 or more) should add 11 to 20 pounds during pregnancy.

However, Gaillard and colleagues say the IOM guidelines are based on a limited number of pregnancy complications and that the new study indicates that obese women should aim for less weight gain than the guidelines.

“Findings from this study suggest that current IOM recommendations may overestimate the optimal amount of weight obese women should gain during pregnancy,” according to the researchers.

“Our findings highlight the importance for further studies focused on the optimal amount of gestational weight gain among severely obese women, also including adverse outcomes such as still birth and infant death, which were not available in our study,” they said.

Zork agrees.

“Most obstetricians believe that for obese patients, gaining up to 20 pounds is excessive,” she said. “We have a lot of data showing that obese women can gain less weight than the IOM recommends without having any complications.”

Even if women don’t lose significant weight before pregnancy, they can still improve their diet for their own health and that of their children.

“A pregnant woman should eat a well-balanced diet of nutritionally beneficial foods and avoid highly processed foods. It’s not about starving yourself, it’s about choosing the right types of food to eat,” Zork said.

“So, instead of reaching for a bag of chips, eat apple slices with peanut butter. We also talk about eliminating sugary beverages and being more active. Small changes in your lifestyle can have a huge impact on your overall health. Seeing a nutritionist can be immensely helpful in coming up with a plan that is doable,” she added.