Epidemiology
Obesity has become an epidemic in most parts of the world and its prevalence in the United States has increased by 75% since 1980. Maternal obesity has been defined in various ways, including bodyweight above 80–114 kg (175–250 lb), a weight 50–300% more than ideal pre-pregnancy weight for height, and a Body Mass Index (BMI) of 25 or above. BMI is a measure of body fat calculated as the weight in kilograms divided by the square of the height in meters. The World Health Organization and the National Institutes of Health define normal weight as a BMI of 18.5–24.9. Overweight is defined as a BMI of 25–29.9 and obesity as a BMI of 30 or greater. Obesity is further characterized as class I (BMI 30–34.9), class II (BMI 35–39.9) and class III (BMI greater than 40). Approximately one half of reproductive-aged women are overweight and one-third are obese. The increased prevalence has been especially notable in non-Hispanic black women (48%), Mexican American women (38%) and non-Hispanic white women (31%). The rates of obesity have also increased dramatically in children as young as 2 years old and in adolescents.
Maternal and fetal complications
Maternal pregravid obesity is a significant risk factor for adverse outcomes in pregnancy. Obesity in the nonpregnant woman is a known risk factor for diabetes mellitus, atherosclerosis and certain malignancies and is the second leading cause of preventable death in the United States. The metabolic syndrome is common in obese women and manifests as hypertension, glucose intolerance and hyperlipidemia. In general, obese women are more insulin resistant than nonobese women and are consequently at significantly greater risk for the development of gestational diabetes mellitus (GDM). Gestational hypertension and pre-eclampsia are also more common in the obese gravida. The increase in the latter two conditions may be related to the presence of the metabolic syndrome. Other conditions complicating pregnancies in obese women include sleep apnea, nonalcoholic fatty liver disease, and chronic renal and cardiac dysfunction.
Numerous studies have found associations between obesity and an increased risk of fetal heart defects, neural tube defects, and omphalocele. The mechanisms underlying these anomalies are not well understood and some believe undiagnosed type 2 diabetes may play a role in the etiology. Unexplained intrauterine fetal death also occurs more frequently in overweight and obese women, even after adjustments for maternal age and exclusion of maternal diabetes and hypertensive disorders. Furthermore, obesity is independently associated with an increased risk of large for gestational age infants and this impact on birthweight increases with increasing BMI.
An obese woman is at significantly higher risk of early miscarriage and recurrent miscarriage following spontaneous conception compared to a normal-weight woman. Even women undergoing assisted reproductive therapy are at increased risk of pregnancy loss. A higher rate of preterm delivery has also been reported in obese women compared to women of normal weight. However, data from more recent studies are conflicting, showing lower rates of spontaneous preterm birth in the obese group.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
