Mama, Mama, How Does Your Belly Grow?

Weight gain during pregnancy can influence risk for pregnancy complications

/ Author:  / Reviewed by: Robert Carlson, M.D Beth Bolt, RPh

(RxWiki News) Nearly all women gain weight during their pregnancy. This is normal and expected since they're growing a little human inside. But gaining too much or too little can present risks.

A recent study found that gaining too much weight during pregnancy can increase women's odds of developing certain pregnancy complications.

Only about one in five women in the study gained the recommended amount of weight during pregnancy, based on 2009 guidelines from the Institute of Medicine.

Most women gained more than was recommended. These women were more likely to develop pre-eclampsia or other high blood pressure disorders during pregnancy.

"Discuss your weight gain with your OB/GYN."

The study, led by Julie Johnson, MD, of the Department of Obstetrics and Gynecology at Brown University in Rhode Island, looked at how pregnant women fared based on the weight they gained during pregnancy.

The researchers specifically used the 2009 guidelines on pregnancy weight gain from the Institute of Medicine (IOM) to guide how they evaluated the participants in the study.

The researchers classified 8,293 pregnant women according to their pre-pregnancy weight using their body mass index (BMI).

BMI is a ratio of a person's height to weight and is used to determine whether someone is a healthy weight or is under- or overweight.

Of the women in the study, 9.5 percent gained less weight than recommended by the IOM guidelines, and 17.5 percent of the women were within the guidelines.

The majority of the women — 73 percent — gained more weight than recommended by the IOM.

The researchers' analysis of the women's risk for various pregnancy complications was adjusted to account for differences in the women's age, race/ethnicity, smoking status and treatment.

Women who exceeded the weight gain recommendations, regardless of their pre-pregnancy weight, were at higher risk for having high blood pressure disorders.

These disorders included pregnancy-induced hypertension and pre-eclampsia. Pre-eclampsia is a pregnancy complication involving high blood pressure and protein in a woman's urine.

For example, the odds that women with a normal pre-pregnancy weight would develop gestational hypertension (high blood pressure during pregnancy) were 1.5 times greater if they gained more weight than recommended, compared to women gaining the recommended amount of weight.

Their odds of developing pre-eclampsia were 2.5 times greater if they gained more weight than recommended.

The risk for women who were overweight before pregnancy were even higher. These women had a risk four times greater for pre-eclampsia if they gained too much weight than if they had gained the recommended amount.

Obese women who gained too much weight during pregnancy were 1.9 times more likely to develop pre-eclampsia than if they stayed within the weight gain guidelines.

Women who were a normal weight or were overweight before becoming pregnant were at a higher risk for having a cesarean section (1.6 to 1.8 times greater odds) if they gained more weight than recommended during pregnancy. 

Their odds of delivering a baby that was large for gestational age were 1.7 to 2.5 times greater if they gained more weight than recommended. Large for gestational age means that the baby had a higher birth weight than what is considered average for the pregnancy week when the baby was born.

These women were less likely than women who did not exceed the weight guidelines to have a baby that was small for gestational age, meaning a baby that had a lower birth weight than what is considered average for the pregnancy week when the baby was born.

The researchers were unable to identify consistent results regarding poor outcomes in women who did not gain enough weight based on the guidelines.

The IOM guidelines for weight gain include the following recommendations:

  • Underweight women (BMI below 18.5) should gain 28 to 40 pounds.
  • Normal weight women (BMI from 18.5 to 24.9) should gain about 25 to 35 pounds.
  • Overweight women (BMI from 25 to 29.9) should gain 15 to 25 pounds.
  • Obese women (BMI of 30 or higher) should gain 11 to 20 pounds.

"The guidelines and supporting recommendations are intended to be used in concert with good clinical judgment and should include a discussion between the woman and her care provider about diet and exercise," the IOM noted in their 2009 report.

Andre Hall, an OBGYN at Birth and Women's Care, PA in Fayetteville, NC, noted that weight gain has always been a sensitive subject, especially with women.

"The subject is no less sensitive when discussing it with women who are pregnant," he said. "On average, women are expected to gain 27-32 pounds during the course of a pregnancy, depending on their pre-pregnancy weight."

However, some women gain more than is appropriate.

"Unfortunately, many women use pregnancy as an excuse to 'give in' to cravings without the same proportion controls they use while not pregnant," Dr. Hall said. "I've often heard comments like 'I'm eating for two now.'"

Yet, Dr. Hall said that gaining too much weight during pregnancy can increase the risk of pregnancy-related complication, such as gestational diabetes and high blood pressure.

"These medical conditions may have significant adverse consequences for both mother and child," he said. "It also leads to larger babies which are at increased risk of birth trauma due to their size. Judicious eating while pregnant, as in the non-pregnant state is an important facet of maintaining a healthy lifestyle."

The study was published in the May issue of the journal Obstetrics and Gynecology.

The research was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the National Heart, Lung and Blood Institute and the National Center for Research Resources. The authors reported no conflicts of interest.

Review Date: 
September 5, 2013
Last Updated:
September 14, 2013