Women With Obesity Do Not Need to Gain Weight During Pregnancy, According to a New Study

Guidelines on weight gain during pregnancy for obese women have long been questioned. New research supports the idea of lowering or eliminating the current recommendation of gaining at least 5 kg. The results were published in The Lancet.

Recommendations for Weight Gain During Pregnancy

International guidelines from the US Institute of Medicine (IOM) state that women with obesity should gain a total of 5 to 9 kg during pregnancy, compared to 11.5 to 16 kg for women of normal weight. The guidelines have long been questioned, but until now there has been no evidence to justify a review. Research from the Karolinska Institute in Sweden shows that weight gain below the current guidelines for women with class 1 and 2 obesity (BMI of 30–34.9 and 35–39.9, respectively) does not pose any increased health risks for mother or child. On the contrary, for women with class 3 obesity (BMI over 40), weight gain below the current guidelines could even be beneficial.

The study supports earlier calls to lower or completely remove the currently recommended minimum weight gain of at least 5 kg, according to Kari Johansson, lecturer at the Institute of Medicine in Solna. “We hope that our research can contribute to a review of national and international guidelines on weight gain during pregnancy,” she says. The study is based on electronic medical records and registry data from 15,760 women with obesity in Stockholm and Gotland (the so-called Stockholm-Gotland Perinatal Cohort). 11,667 of the women in the study had grade 1 obesity, 3,160 had grade 2 obesity, and 933 had grade 3 obesity. The study included singleton pregnancies delivered between 2008 and 2015. The women were followed up after delivery for an average of eight years.

Ten known adverse events associated with weight gain during pregnancy were examined: preeclampsia, gestational diabetes, excessive weight gain after birth, maternal cardiometabolic disease, unplanned cesarean delivery, preterm birth, large or small birth weight, stillbirth, and infant death. These adverse events were weighted according to their severity and combined into an adverse composite outcome.

Overall, the study shows that women with class 1 and 2 obesity do not have an increased risk of the adverse composite outcome when weight gain is below the current IOM guidelines. In women with class 3 obesity, however, weight gain below the guidelines or weight loss was associated with a reduced risk of the adverse composite outcome. For example, no weight gain (i.e., 0 kg) was associated with a risk reduction of approximately 20 percent. On this basis, the researchers concluded that weight gain below current recommendations is likely to be safe in pregnancies with obesity and may even be beneficial for women with grade 3 obesity. The results also show that specific recommendations are needed for women with grade 3 obesity.