Rates of obesity are continuing to rise dramatically in developed countries, including an increased prevalence of morbid obesity (body mass index [BMI] >35). This trend has led to a concurrent increase in health concerns for women of reproductive age, and it is now well established that weight gain and obesity cause major comorbidities in pregnancy that contribute to adverse maternal and neonatal outcomes.
The Institute of Medicine recommends use of BMI to classify maternal weight groups, using prepregnancy height and weight. According to the classification by the World Health Organization, obesity is defined as a BMI above 29 kg/m2. Other definitions of obesity found in the literature include women who are 110 to 120 percent of their ideal body weight or weigh more than 91 kg (200 lb).
To reduce risk and complications of weight gain in pregnancy, women should set pregnancy weight goals according to Table 24-1.
TABLE 24-1:PREGNANCY WEIGHT GAIN ACCORDING TO BMI ||Download (.pdf) TABLE 24-1: PREGNANCY WEIGHT GAIN ACCORDING TO BMI
| ||BMI (kg/m2) ||Weight Gain (kg) ||Weight Gain (lb) |
|Underweight ||<18.5 ||12.5-18 ||28-40 |
|Normal weight ||18.5-24.9 ||11.5-16 ||25-35 |
|Overweight ||25.0-34.9 ||7-11.5 ||15-25 |
|Obese ||>30 ||5-9 ||11-20 |
If obesity is seen in prepregnancy counseling, recommendations are made about diet and lifestyle modifications. Bariatric surgery is also recommended in prepregnancy counseling because it has been shown to result in significant weight loss, which can improve pregnancy outcomes. Studies have shown that bariatric surgery also reduces hypertension, preeclampsia, and macrosomia.
Obese mothers have an increased incidence of medical complications, such as hypertension, diabetes mellitus, and obstructive sleep apnea. Obese mothers also have a higher rate of predisposing medical issues, which is what contributes to a higher rate of labor induction in this group or operative delivery.
There is still conflicting and limited studies on labor characteristics in obese gravid women. The best evidence suggests that obese women have longer labors. In a cohort study of nulliparous women, as maternal weight increased, the rate of cervical dilatation decreased, and the induction to delivery interval was longer. Increased duration of labor does not seem to be due to maternal poor expulsive efforts. A recent study showed that obese nulliparous women were found to have a higher rate of cesarean section in the first but not the second stage of labor. Therefore, pushing out the baby is not the issue, but getting to the second stage is.