Gestational weight gain (GWG) — the weight you gain during pregnancy — is normal, even welcomed in some cases. But according to a new report from the Centers for Disease Control and Prevention (CDC), nearly half of all pregnant women in the United States are putting on more pounds than they should.

Right now, the Institute of Medicine offers pregnant women GWG guidelines based on their body mass index (BMI) pre-pregnancy. For example, women with a normal BMI (18.5 to 24.9) should gain 25 to 30 pounds, while women with a lower-than-normal BMI (below 18.5) should gain 28 to 40 pounds. As for women who are overweight and obese, the IOM recommends only gaining between 11 and 20 pounds.

These guidelines are in place because the weight a woman gains during pregnancy "has important health implications for both mother and child," the CDC reported. IOM's guidelines in particular are meant to "promote optimal health by balancing risks associated with too much or too little weight gain." While a recent study found that 21 percent of pregnant women gain less than the recommend amount of weight, and 47 percent gain more, the CDC found researchers didn't observe this prevalence on a state level.

So, they analyzed 2013 birth data for U.S. resident women who delivered full-term (37–41 weeks gestation) infants from 43 jurisdictions: 41 states, New York City, and the District of Columbia. In addition to referencing the 2003 birth certificate for maternal height, pre-pregnancy weight, and delivery weight, researchers also considered 2012 data from the Pregnancy Risk Assessment Monitoring System (PRAMS) in order to "estimate prevalence for five states with available data that had not yet adopted the 2003 birth certificate."

The results showed only one third of women had gained an "appropriate" amount of weight, whereas 20 percent had gained an "inadequate" or "excessive amount." In fact, excessive weight gain was more prevalent than inadequate or appropriate weight gain in every state. Numbers-wise, 47.5 percent of women gained an excessive amount of weight during pregnancy, with lower rates in New Jersey and higher rates in Missouri.

Women who had a low- or normal-BMI prior to becoming pregnant had gained 23.5 and 37.6 percent more weight, respectively, and women who were overweight or obese gained up to 61.6 percent more weight.

"Gestational weight gain outside the IOM recommendations has important short- and long-term health consequences for mothers and infants," the CDC said. "Whereas, inadequate GWG increases the risk for low birth weight; excessive GWG increases the risk for macrosomia, postpartum weight retention, future maternal obesity, and possibly future childhood obesity.”

The CDC added that excessive weight gain often begins early in pregnancy, yet most women only need to consume an additional 340-450 calories per day during their second and third trimesters. Thus, the CDC urges clinicians, nurses, and nutrition specialists work to implement early education and interventions that "might promote appropriate GWG combine several strategies, including dietary goals, physical activity, routine self-monitoring of weight, and frequent provider contact."

Physical activity may be an especially important focus given many women fear keeping up with their pre-pregnancy routine can be harmful to health. However, several studies haved dispelled this myth (click here and here) and conclude pregnant women are safe to do moderately intense workouts, like brisk walking and yoga. The CDC itself recommends 150 minutes of this kind of exercise per week. And to some experts, exercise is the greatest way to deter excessive GWG.

The CDC report concludes: "To improve maternal and child health, intensified, multifaceted strategies are important for increasing the proportion of women who achieve appropriate GWG."

Source: Nicholas P. Deputy, MPH1,2,3; Andrea J. Sharma, PhD1; Shin Y. Kim, MPH1Gestational Weight Gain — United States, 2012 and 2013. Centers for Disease Control and Prevention. 2015.