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The prevalence of obesity has increased substantially over the past 10 years and affects more than one-third of the population in the United States. The rates of extreme obesity (body mass index [BMI] > 40) have had the fastest rate of increase, now affecting up to 8% of the population. All levels of obesity affect more persons in the southern United States than in other regions, and non-Hispanic black women are disproportionately represented compared to other ethnicities, with 50% affected. Mexican American women follow closely at 45%, and 33% of non-Hispanic Caucasian women are obese.

Obesity presents many challenges prior to pregnancy, and weight loss prior to conception has many proven benefits. Preconception counseling is of benefit in these patients. There are risks to pregnancy at the time of conception, as well as during the first trimester, and counseling about these risks prior to pregnancy would allow the patient the opportunity to make lifestyle changes that would benefit her and improve obstetrical outcome. There are several limitations during pregnancy in regard to prenatal diagnosis, and accurate determination of certain risks to the fetus may be more difficult to ascertain than in the nonobese population. The risks of certain prenatal diagnostic procedures are increased, and the limitations of prenatal imaging by ultrasound for diagnosis of certain types of fetal abnormalities worsen. This chapter focuses on preconception counseling as well as the difficulties of prenatal testing in this group of patients. Difficulties later in pregnancy are covered elsewhere in this book.


Obesity is defined by BMI level, and normal weight is defined as a BMI of 18.5–24.9. The Institute of Medicine (IOM) recently published pregnancy weight gain guidelines based on prepregnancy BMI.1 The recommendations are independent of age, parity, smoking history, race, and ethnic background. The IOM guidelines define overweight as a BMI of 25–29.9, and obesity as a BMI greater than 30. IOM does not differentiate between the higher classes of obesity, which are separated into class I (BMI 30–34.9), class II (BMI 35–39.9), and class III (BMI > 40). The risks during pregnancy are affected by extreme obesity and increase with increasing degree of obesity.

Preconception counseling is important for all women, but especially for obese women, particularly as they reach class II or class III obesity. The risk of gestational diabetes, for example, increases from an odds ratio of 2.6 (confidence interval [CI] 1.2–3.9) for women who are class I to (CI 1.5–5.9) for women with class III (OR = 4). The risk of preeclampsia increases from 1.6 (class I) to 3.7 (class III) (CI 0.90–2.2 and 1.85–4.4, respectively), and fetal macrosomia increases from an odds ratio of 1.7 (class I) to 2.9 (class III) (CI 1.3–2.6 and 1.8–3.8, respectively). The risk of Cesarean section ranges from 20.7% for women with a BMI of 29.9 or less to 33.8% for women with a BMI of ...

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