In the United States, about half of all pregnant women are overweight or obese. A recent study indicates that higher prepregnancy body mass index (BMI) is associated with a higher risk of maternal morbidity. 

In this study carried out in Washington State, 743,630 women were included. Prepregnancy BMI was distributed as follows: underweight, 3.2%; normal weight, 47.5%; overweight, 25.8%; obesity class 1, 13.1%; obesity class 2, 6.2%; and obesity class 3, 4.2%.

Rates of severe maternal morbidity were the highest in both underweight and overweight women, with the following adjusted odds ratios (ORs): 1.2 (95% CI, 1.0-1.3) for underweight women; 1.1 (95% CI, 1.1-1.2) for overweight women; 1.1 (95% CI, 1.1-1.2) for women with class 1 obesity; 1.2 (95% CI, 1.1-1.3) for women with class 2 obesity; and 1.4 (95% CI, 1.3-1.5) for women with class 3 obesity, as compared to women with normal BMI.

These findings are statistically significant, although result in a relatively small absolute increase in risk.  However, it is noteworthy that there appears to be a dose-response effect, such that the rates of maternal morbidity rose as prepregnancy BMI increased.

This may be a particularly important issue in women with psychiatric illness who are pregnant or planning to conceive.  Women with psychiatric disorders have a higher risk of obesity than women in the general population.  Higher BMI may be related to the illness itself or lifestyle factors associated with psychiatric illness; however, we have seen that women taking certain psychotropic medications, particularly the second generation or atypical antipsychotic medications, enter into pregnancy with a higher BMI and are therefore at greater risk for adverse outcomes.    

The big question is how to best reduce risk of obesity and weight gain in this population. Many interventions focus on weight gain during pregnancy; however, there may be risks associated with weight loss during pregnancy.  Thus, one could argue that the ideal time to intervene is before pregnancy.  

A study at MGH is investigating a new lifestyle intervention to help women with a history of depression who are either pregnant or  trying to conceive to learn to exercise, eat well, and live a healthy lifestyle. If you are interested in participating or would like additional information, please call Samantha at 617-643-2076 or visit the MGH Clinical Trials site.

Ruta Nonacs, MD PhD


Lisonkova S, Muraca GM, Potts J, Liauw J, Chan WS, Skoll A, Lim KI.  Association Between Prepregnancy Body Mass Index and Severe Maternal Morbidity.  JAMA. 2017 Nov 14;318(18):1777-1786.

Read More:

Low and High Prepregnancy BMI Raise Maternal Mortality (Medscape – free subscription)