Obesity is characterized by having very high body fat content relative to lean body mass. The National Heart, Lung, and Blood Institute (NHLBI), in cooperation with the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) (NHLBI, 1998) and the World Health Organization (WHO; 2011), define obesity as a body mass index (BMI) of ≥30 kg/m². Normal body weight is defined as a BMI or weight (kg)/height (m²) of 18.5 to 24.9, overweight as BMI of 25.0 to 29.9, obese as BMI of 30.0 to 39.9, and extremely (morbidly) obese as BMI ≥40.0 (NHLBI, 1998; WHO, 2011). See Table 12-1 for a summary of BMI criteria for classifying weight status.

Obesity has become a worldwide public health problem, prevalent in both developed and developing countries (Knight, Kurinczuk, Spark, & Brocklehurst, 2010). There are more than 1.5 billion overweight adults in the world; 300 million meet criteria for obesity (WHO, 2011). Approximately 65% of the world’s population live in countries where overweight and obesity are responsible for more deaths than underweight (WHO, 2011). The global epidemic of obesity is of great concern, especially in the United States, where two thirds of adults are either overweight or obese as compared to slightly under half of adults in developing countries with weight problems (Berrington de Gonzalez et al., 2010). Based on data from the 2009 to 2010 National Health and Nutrition Examination Survey (Ogden, Carroll, Kit, & Flegal, 2012), it is estimated that 68% of adults 20 years of age or older in the United States are overweight, 35.7% are obese, and 5.7% are extremely obese. There are currently more obese adults in the United States than at any other time in our history. Over the last 30 years, the rate of obesity has doubled for adults and tripled for children (Gunatilake & Perlow, 2011). There now appears to be a slowing of the rate of increase or even a leveling off of obesity, particularly for women (Flegal, Carroll, Ogden, & Curtin, 2010). While there has been a considerable increase in obesity among men and boys of the last decade, prevalance of obesity among women and girls has remained essentially the same (Flegal et al., 2010). Based on comparison of data from 1999 to 2000 and 2009 to 2010, differences in prevalence of obesity between men and women have diminished significantly (Flegal et al., 2010; Ogden et al., 2012). There was no change in the prevalence of obesity in the United States among adults or children from 2007-2008 to 2009-2010 (Ogden et al., 2012). In the United States, risk of becoming overweight is approximately 50%; risk of obesity is estimated to be 25% (Duran, 2011). See Display 12-1 for a list of risk factors for developing obesity (Duran, 2011).

While the etiology of obesity may be very basic, for example, an energy imbalance due to taking in more calories than energy expended, there are multiple complex factors contributing to the increase in obesity in the United States. These factors occur at all social, economic, and environmental levels (Centers for Disease Control and Prevention [CDC], 2011). Body weight is the result of genes, metabolism, behavior, environment, culture, and socioeconomic status (Chescheir, 2011). A significant factor related to the current prevalence of obesity is the evolution of the human species, which occurred in an environment where few calories were available and a significant expenditure of energy
was needed to acquire those calories (Phelan, 2010). To ensure survival of the species, humans needed to store fat for times when resources were limited. Women specifically needed to have adequate stores of fat to sustain a pregnancy and breastfeed their newborns (Phelan, 2010). As a result, the human body is quite efficient in using calories and has no limit in storing excessive caloric intake in the form of fat. Humans may be predisposed to preferring sweet foods that are calorie dense and require a relatively low expenditure of energy to obtain (Phelan, 2010). Some scientists hypothesize that certain DNA are responsible for consumption of sugary foods and are linked to obesity-related illnesses such as diabetes (Daniels, 2006). Storing unlimited amounts of fat may have been a useful trait in the early days of evolution when humans were hunters and gatherers, but it has not been shown to be advantageous in today’s environment where many occupations are sedentary, physical activity is limited, and minimal energy is required to acquire high-calorie food (Phelan, 2010). American society has become characterized by environments that promote physical inactivity and increased consumption of less-healthy food (CDC, 2011; Chescheir, 2011). The increased intake of energy-dense foods that are high in fat, salt, and sugars but low in vitamins, minerals, and other micronutrients combined with the decrease in physical activity due to the increasingly sedentary nature of many forms of work, changing modes of transportation, and increasing urbanization have not been beneficial in promoting human health (WHO, 2011).

Costs and availability of healthy foods are other factors contributing to obesity (CDC, 2011; Phelan, 2010). Healthy foods, including lean meats, fish, fresh fruits, and vegetables, cost more than fast food meals, which can easily exceed 1,000 calories for $5 or less. Energy-dense foods with increased calorie, fat, and sugar content are associated with poverty as they are less expensive (Black, 2009). Grocery stores in which fresh foods are available are often not located in the most economically depressed areas, leaving some members of society with few options for good nutrition on a routine basis (American College of Obstetricians and Gynecologists [ACOG], 2010; CDC, 2011). Therefore, women of lower income and certain racial and ethnic groups have higher rates of obesity (Ogden & Carroll, 2010).

As a chronic disease, obesity represents a significant economic burden to society. It is estimated that obesity is responsible for an annual cost of $198 billion in the United States, with an additional $72 billion related to those who are overweight but not obese (Society of Actuaries [SOA], 2011). These economic costs include medical care ($127 billion), loss of worker productivity due to higher rates of death ($49 billion), loss of productivity due to disability of active workers ($43 billion), and loss of productivity due to total
disability ($72 billion) (SOA, 2011). The high healthcare costs are related to the comorbidities and medical complications associated with obesity and the sheer number of obese individuals. Obesity is linked to many significant diseases, such as hypertension, coronary heart disease, type 2 diabetes, gastroesophageal reflux disease, gallbladder disease, asthma, osteoarthritis, stroke, sleep apnea, thromboembolic events, elevated lipids, certain cancers (endometrial, breast, and colon) and psychological disorders such as depression (Reece, 2008; Vallejo, 2007). See Figure 12-1. Obesity-related deaths are mostly the result of diabetes, heart disease, hypertension, and cancer and estimated to account for 100,000 to 300,000 U.S. deaths every year (Duran, 2011).

Ethnicity and U.S. geographic region are factors that influence risk of obesity, based on a summary of data from 2006 to 2008 from the CDC (Odgen & Carroll, 2010). Obesity disproportionally affects minority women. Non-Hispanic blacks have a 51% higher prevalence of obesity compared with non-Hispanic whites. Hispanics have a 21% higher prevalence of obesity compared with non-Hispanic whites. The highest rate of obesity is among non-Hispanic black women at 49.6%, followed by 45.1% of Mexican American women, 36.8% of all Hispanic women, and 33.0% of non-Hispanic white women (Ogden & Carroll, 2010). Obesity in each of these groups has increased over the last 20 years (Ogden & Carroll, 2010). The prevalence of obesity for non-Hispanic whites as well as non-Hispanic blacks is highest in the Midwest and South (Ogden & Carroll, 2010). The highest prevalence for obesity in the Hispanic population is in the Midwest, South, and West (Ogden & Carroll, 2010). There are 39 states with obesity prevalence ≥25% and 9 states (Alabama, Arkansas, Kentucky, Louisiana, Mississippi, Missouri, Oklahoma, Tennessee, and West Virginia) with ≥30% (Ogden & Carroll, 2010). Only Colorado and the District of Columbia have obesity prevalence less than 20%. In the United States, obesity is rapidly approaching tobacco as the leading cause of preventable death (Rahman & Berenson, 2010).

It is estimated that 31.9% of U.S. reproductive age women from 20 to 39 years old are obese; 7.6% of these women are morbidly obese, defined as a BMI of ≥40 (CDC, 2011; Wolfe, Rossi, & Warshak, 2011). Obesity in pregnancy has increased concurrently with obesity in the general population. Approximately 30% of pregnant women are obese (CDC, 2011). Further, it is estimated that 8% of pregnant women meet criteria for morbid obesity (Gunatilake & Perlow, 2011).

During the reproductive years, women are usually at peak health, which can accommodate the dramatic physiologic changes of pregnancy and the physical challenges of birth. However, more women are becoming pregnant who have preexisting medical conditions such as obesity. Pregnancy can exacerbate obesity-related comorbidities such as hypertension and/or diabetes as well as result in the development of additional maternal complications during pregnancy, labor, and birth (Wolfe et al., 2011). Maternal morbidity and mortality increase with increasing BMI (Mantakas & Farrell, 2010; Vallejo, 2007). Women may develop lifelong obesity as a result of excessive pregnancy weight gain and postpartum weight retention (Davis & Olson, 2009).

Obesity during pregnancy increases the risk of morbidity and mortality for both the mother and baby (see Display 12-2).The obese woman has an increased risk of spontaneous abortion, gestational diabetes, preeclampsia, labor abnormalities, operative vaginal or cesarean birth, anesthesia complications, wound infections, deep vein thrombosis, respiratory complications such as asthma and obstructive sleep apnea, medically indicated preterm birth, postterm pregnancy, urinary tract infections, and birth trauma related to macrosomic infants and fourth-degree lacerations (ACOG, 2013a; Blomberg, 2011; Catalano, 2007; Chescheir, 2011; Ehrenberg, 2011; Hendler et al., 2005; Jungheim & Moley, 2010; Ovesen, Rasmussen, & Kesmodel, 2011; Stream & Sutherland, 2012; Tan & Sia, 2011; Thornburg, 2011; Vidarsdottir, Geirsson, Hardardottir, Valdimarsdottir, & Dagbjartsson, 2011). An obese pregnant woman is much more likely to develop gestational diabetes than a woman of normal weight (Chu et al., 2007; Davis & Olson, 2009; Saldana, Siega-Riz, Adair, & Suchindran, 2006). Hypertensive disorders of pregnancy are more common in obese women. An increase of 5 to 7 kg/m² BMI nearly doubles the risk
of preeclampsia (O’Brien, Ray, & Chan, 2003). Operative and postoperative complications are increased with maternal obesity as well, including as a longer operative time; prolonged time from incision to birth of the baby; and increased blood loss, wound infection, and uterine dehiscence (Duran, 2011).

Maternal death is also associated with obesity (Goffman, Madden, Harrison, Merkatz, & Chazotte, 2007). Overweight and obese women are overrepre-sented among women who die during or within 1 year of a pregnancy. More than half of women who died during or after pregnancy between 2003 and 2005 in the United Kingdom were overweight or obese; 15% were morbidly or extremely obese (Centre for Maternal and Child Enquiries [CMACE], 2011). Obese pregnant women are estimated to be at four to five times greater risk of suffering maternal death than a woman of normal weight (CMACE, 2011). Racial disparities found with other health and illness indicators are also present in maternal deaths. A review of maternal deaths in Virginia from 1999 to 2002 revealed that the maternal mortality ratio for overweight and obese African American women was 2.2 times higher than for overweight or obese Caucasian women (Virginia Maternal Mortality Review Team, 2009). The same obesity-related diseases that are associated with death in the general population are also associated with maternal mortality. Many of the obese women who died in the Virginia case series report
had other chronic health conditions that are caused or exacerbated by obesity (Virginia Maternal Mortality Review Team, 2009). Nearly one third of overweight and obese women who died had cardiac disorders or gestational hypertension, preeclampsia, or eclampsia (Virginia Maternal Mortality Review Team, 2009).

The risk of spontaneous abortion and recurrent spontaneous abortion in the obese population is twice that of their non-obese counterparts (Thornburg, 2011). Extremely obese women may be at 40% greater risk of stillbirth than a normal weight woman (Salihu et al., 2007; Salihu, 2011). It is hypothesized that hyperlipidemia of obesity may lead to atherosclerotic changes in the placental vessels. This change combined with sleep apnea, leading to desaturation and decreased perception of fetal movement due to body habitus, may contribute to the increased rate of stillbirth in this population (Society of Obstetricians and Gynaecologists of Canada [SOGC], 2010).

The fetus of an obese woman is at increased risk for congenital anomalies, macrosomia, and fetal death. Excessive maternal weigh and obesity have a negative effect on uterine contractility (Zhang, Bricker, Wray, & Quenby, 2007), which may explain why these women have a lower rate of spontaneous preterm birth (Hendler et al., 2005). However, the comorbidites associated with overweight and obesity such as hypertensive disorders and diabetes predispose overweight and obese women to medically indicated preterm birth and their babies to the sequelae of prematurity (Hendler et al., 2005). Multiple congenital anomalies have been associated with maternal obesity, such as neural tube defects, cardiovascular anomalies, cleft lip and palate, diaphragmatic hernia, and gastroschisis (Gunatilake & Perlow, 2011). Evidence suggests that the risk of malformations increases proportionate to the level of obesity (Gunatilake & Perlow, 2011). Macrosomic infants are exposed to an increased risk of birth trauma from shoulder dystocia. Due to the increased risk of medically indicated preterm birth associated with the comorbidities of obesity such as diabetes and hypertensive disorders, babies of obese women are at increased risk for the neonatal complications related to prematurity, including respiratory distress, cardiac problems, intracranial hemorrhage, and vision and intestinal problems (James & Maher, 2009).

Excessive weight gain during pregnancy appears to create an intrauterine environment that promotes larger babies with more fat cells, which in turn puts the baby at higher risk for obesity during childhood and as an adult with all the long-term consequences (Phelan, 2010). There is evolving evidence about the developmental origins of disease that has implications for fetuses of women who gain excessive weight during pregnancy. When the fetus is subjected to an environment during pregnancy characterized by nutritional factors contributing to excessive maternal weight gain, fetal programming, that is, the process in which a stimulus in utero establishes a permanent response in the fetus, can lead to increased susceptibility to disease in childhood and throughout life (Catalano, 2007). Children born to obese mothers are twice as likely to develop obesity at 2 to 4 years of age (Whitaker, 2004). Primarily due to the obesity epidemic, U.S. children born now are projected to have a shorter life span than their parents (Phelan, 2010). Excessive weight gain during pregnancy results in a negative cycle of adverse health as obese women give birth to macrosomic daughters who are more likely to become obese themselves and deliver large babies (Artal, Lockwood, & Brown, 2010).

The risk for offspring of obese women extends past the pregnancy. Children born of obese mothers are at increased risk for diabetes, heart disease, and long-term obesity (Gunatilake & Perlow, 2011). Several studies have noted an association between birth weight and childhood obesity (Baird et al., 2005; Hui et al., 2008; Phelan et al., 2011). Research has shown a close association between large-for-gestational-age (LGA) babies and childhood obesity in African American, inner city single mothers of low income and education, putting this population at high risk (Mehta, Kruger, & Sokol, 2011). The United States has launched programs to address childhood obesity. These efforts are aimed at school foods and activity level of schoolchildren, food marketing, taxation, and reducing sedentary time at a computer or television (Ogden, Carroll, Curtin, Lamb, & Flegal, 2010). Since the antenatal period is further implicated in contributing to the obesity of children, more emphasis is needed on counseling mothers on the association between the effects of pregnancy and obesity to address some of the modifiable risk factors before pregnancy occurs (Mehta et al., 2011).

Weight loss and modification of nutritional intake before pregnancy reduce risk of obesity and the related potential complications for the mother and baby (American Academy of Pediatrics [AAP] & ACOG, 2012; CDC, 2006). Preconception care that includes risk screening, health promotion counseling, and interventions based on individual patient status enables women to enter pregnancy in optimal health (CDC, 2006). Therefore all pregnant women, including those that are overweight or obese, should have a preconception visit to their obstetrical care provider to assess health status; evaluate physical, emotional, and nutritional readiness for pregnancy; and allow for modification of potential risk factors and behaviors (CDC, 2006). Obesity increases risk of early miscarriage by twofold to threefold and decreases success of fertility treatments; therefore, obese women planning pregnancy should be counseled that achieving a successful pregnancy may be more difficult (Jungheim & Moley, 2010;
Thornburg, 2011). Women who have had bariatric surgery should be advised to wait 12 to 24 months before attempting pregnancy as this time frame is the period of the most rapid weight loss, which can be detrimental to the growing fetus (ACOG, 2009a). During the preconception visit, the woman’s height and weight should be recorded so BMI can be calculated (AAP & ACOG, 2012).

Counseling an obese woman who is planning pregnancy should include information regarding maternal and fetal risks associated with obesity, screening for diabetes and hypertension, nutrition counseling, encouragement of exercise, and consultation with a weight loss specialist before attempting pregnancy. This counseling should take into consideration the woman’s food preferences, eating patterns, cultural beliefs, and access to healthy food (AAP & ACOG, 2012). Referral to a dietitian may be indicated for women who are overweight or obese. Obese women considering pregnancy should be encouraged to follow an exercise program (AAP & ACOG, 2012). Follow-up visits with healthcare providers to monitor lifestyle changes in nutrition and physical activity prior to pregnancy may be warranted.

Preconception weight loss with possible resolution of hypertension, hyperlipidemia, and diabetes most likely will improve both maternal and fetal outcomes during pregnancy, labor, birth, and the postpartum period (CDC, 2006). Establishing a healthy diet and physical activity program prior to pregnancy may translate into maintaining these beneficial lifestyle changes during the pregnancy and beyond. The fetus and newborn may have less risk of maternal obesity-related problems when the mother adopts a healthier lifestyle. Weight loss will also decrease the lifelong disease burden for the woman (Gunatilake & Perlow, 2011).