Excessive weight has become one of the major health problems in affluent societies. Because of its medical importance and its multifaceted effects on pregnancy, it is discussed separately in this chapter. The prevalence of obesity in the United States has increased steadily as economic prosperity has increased. For a number of years, obesity has been termed epidemic—strictly defined, this implies a temporary widespread outbreak of greatly increased frequency and severity. Unfortunately, obesity more correctly is endemic—a condition that is habitually present. Moreover, its prevalence has continued to increase since 1960. By 1991, approximately a third of adults in the United States were overweight, and almost 300,000 deaths were attributed annually to obesity (Allison and co-workers, 1999). Sadly, the problem is not limited to adults, and 15 percent of children aged 6 through 11 years are reported to be overweight (Ogden and associates, 2002). The prevalence in adolescents is similar.
Public health authorities began to address the problem of obesity in the late 1980s. A stated goal of Healthy People 2000 was to reduce the prevalence of overweight people to 20 percent or less by the end of the 20th century (Public Health Service, 1990). Not only was this goal not achieved, but by 2000, more than half of the population was overweight, and nearly a third of adults were obese (Flegal and colleagues, 2002; Hedley and associates, 2004).
There are many obesity-related diseases, including diabetes, heart disease, hypertension, stroke, and osteoarthritis. Together they result in a decreased life span. The worldwide diabetes epidemic that Bray (2003) predicted would follow the worldwide obesity epidemic has already begun. Obese women who become pregnant—and their fetuses—are predisposed to a variety of serious pregnancy-related complications. Long-term maternal effects include significant and increased rates of morbidity and mortality. Moreover, recent studies show that the offspring of obese women also suffer long-term morbidity.
A number of systems have been used to define and classify obesity. The body mass index (BMI), also known as the Quetelet index, is currently in use. The BMI is calculated as weight in kilograms divided by height in square meters (kg/m2). Calculated BMI values are available in various chart and graphic forms, such as the one shown in Figure 43-1. According to the National Heart, Lung, and Blood Institute (1998), a normal BMI is 18.5 to 24.9 kg/m2; overweight is a BMI of 25 to 29.9 kg/m2; and obesity is a BMI of 30 kg/m2 or greater. According to Freedman and colleagues (2002), obesity is further categorized as class I (BMI: 30 to 34.9 kg/m2), class II (BMI: 35 to 39.9 kg/m2), and class III (BMI: 40-plus kg/m2).
Chart for estimating body mass index (BMI). To find the BMI category for a particular subject, locate the point at which the height and weight intersect.
Pleis and colleagues (2003) reported that by 2000, 34 percent of adults in the United States were overweight, and another 27 percent were obese. This is an increase of 75 percent compared with 1980 statistics. Thus, by 2000, more than half of adults in the United States were either overweight or obese. Moreover, 2.8 percent of women and 1.7 percent of men were extremely obese (class III), with a BMI of 40 kg/m2 or more (Mokdad and associates, 2003). Prevalence data through 2004 for women aged 20 to 39 are shown in Figure 43-2. As shown in Figure 43-3, there is a disparate prevalence of obesity in Mexican-American and black women ages 20 to 39. This is also true among indigent individuals (Drewnowski and Specter, 2004). The prevalence of obese adults in 2006 was less than 20 percent in only four states (Centers for Disease Control and Prevention, 2007, 2008).
Prevalence (percent) of obesity among 20- to 39-year-old nonpregnant U.S. women. Obesity is defined as a body mass index of greater than 30 kg/m2 (Redrawn with permission from Influence of Pregnancy Weight on Maternal and Child Health Workshop Report, 2007, by the National Academy of Sciences, Courtesy of the National Academies Press, Washington, D.C.)
Prevalence (percent) of obesity among U.S. nonpregnant women, aged 20 to 39, by race/ethnicity for 2003-2004. Obesity is defined as a body mass index of greater than 30 kg/m2. (Redrawn with permission from Influence of Pregnancy Weight on Maternal and Child Health Workshop Report, 2007, by the National Academy of Sciences, Courtesy of the National Academies Press, Washington, D.C.)
In some people, obesity interacts with inherited factors and leads to the onset of insulin resistance. This metabolic abnormality in turn is responsible for altered glucose metabolism and a predisposition to type 2 diabetes. In addition, it causes a number of subclinical abnormalities that predispose to cardiovascular disease and accelerate its onset. The most important among these are type 2 diabetes, dyslipidemia, and hypertension. When clustered together with other insulin resistance–related subclinical abnormalities, these are referred to as the metabolic syndrome (Abate, 2000). Virtually all obese women with hypertension demonstrate elevated plasma insulin levels. Levels are even higher in women with excessive fat in the abdomen—an apple shape, compared with those whose fat is in the hips and thighs—a pear shape (American College of Obstetricians and Gynecologists, 2003). In fact, Gus and associates (2004) reported that for women, a waist circumference greater than 88 cm was more predictive ...