Maternal fetal medicine expert Loralei L. Thornburg, M.D., dishes out on the truths and myths about the pregnancy-related changes and obstacles obese women may face in the journal Seminars in Perinatology.

"I treat obese patients all the time, and while everything may not go exactly as they'd planned, they can have healthy pregnancies," says Thornburg, who specializes in the care of high-risk pregnancies and conducts research on obesity and pregnancy. "While you can have a successful pregnancy at any size, women need to understand the challenges that their weight will create and be a partner in their own care; they need to talk with their doctors about the best way to optimize their health and the health of their baby."

Fact or myth?

1. Many obese women are vitamin deficient.

Fact

Forty percent are deficient in iron, 24 percent in folic acid and 4 percent in B12. This is a concern because certain vitamins, like folic acid, are very important before conception, lowering the risk of cardiac problems and spinal defects in newborns. Other vitamins, such as calcium and iron, are needed throughout pregnancy to help babies grow.

Thornburg says vitamin deficiency has to do with the quality of the diet, not the quantity. Obese women tend to stray away from fortified cereals, fruits and vegetables, and eat more processed foods that are high in calories but low in nutritional value.

"Just like everybody else, women considering pregnancy or currently pregnant should get a healthy mix of fruits and vegetables, lean proteins and good quality carbohydrates. Unfortunately, these are not the foods people lean towards when they overeat," noted Thornburg. "Women also need to be sure they are taking vitamins containing folic acid before and during pregnancy."

Fact or myth?

2. Obese patients need to gain at least 15 pounds during pregnancy.

Myth

In 2009, the Institute of Medicine revised its recommendations for gestational weight gain for obese women from "at least 15 pounds" to "11-20 pounds." According to past research, obese women with excessive weight gain during pregnancy have a very high risk of complications, including indicated preterm birth, cesarean delivery, failed labor induction, large-for-gestational-age infants and infants with low blood sugar.

If a woman starts her pregnancy overweight or obese, not gaining a lot of weight can actually improve the likelihood of a healthy pregnancy, Thornburg points out. Talking with your doctor about appropriate weight gain for your pregnancy is key, she says.