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 30–34.9 and 47.4% for women with a BMI of 40.² There is also an increased risk of spontaneous abortion in obese women, in both those who conceive spontaneously and those undergoing fertility treatments.

Encouraging weight loss in these women may substantially reduce their risk of obstetric complications. All studies that have compared pregnancy outcomes for obese women to those for patients who underwent an active weight loss program prior to conception showed a significantly decreased rate of obstetric complications in those who lost at least 10% of their prepregnancy weight or decreased their class of obesity by 1 level. There does not appear to be any threshold below which there is a higher chance of better outcomes, but it appears that in the obesity class III set of patients, even a modest weight loss of 5% shows a decrease in the rate of development of gestational diabetes, premature delivery, and hypertensive complications.³

As with any nonpregnant obese individual, a baseline electrocardiogram (ECG) and echocardiogram are suggested when a women presents for preconception or prenatal care. This is particularly true in the first trimester of pregnancy, as these patients may have underlying cardiomyopathy from prolonged obesity and may have hypertension. The higher-class obese patients may exhibit a “Pickwickian”-type syndrome and be chronically short of breath, be polycythemic, and have hypertrophic cardiomyopathy. In addition, if a patient requires more than 2 pillows to sleep at night or there is evidence of excessive snoring or sleep apnea, a sleep study should be undertaken to determine if there are any issues with chronic airway obstruction. These obstructive airway issues will worsen during the course of pregnancy with the gravid uterus and physiologic airway changes, and many of these patients will benefit from a continuous positive airway pressure (CPAP) machine for sleep.

Counseling of these women is also important to inform them of potential fetal risks. The risks of stillbirth⁴ and certain congenital defects, such as neural tube defects (NTDs), are increased, and 1 study of 2900 obese women suggested a lower rate of prematurity.⁵ Other studies^4,6 have suggested higher rates of premature delivery in obese women compared to normal-weight women. Many of these preterm deliveries are iatrogenic due to pregnancy complications caused by obesity, such as preeclampsia, hypertension, and gestational diabetes. A Swedish study⁴ showed that if women with a BMI greater than 25 optimized their BMI prior to pregnancy, there was a 13% reduction in risk of stillbirth. A meta-analysis of 9 observational studies showed that women who were overweight or obese before pregnancy were at greater risk of stillbirth. The odds ratio for overweight women was 1.47 (CI 1.08–1.94) and for obese women was 2.07 (CI 1.59–2.74). As women are more likely to remain obese at the time of conception and during pregnancy, it is unclear if weight loss during pregnancy confers the same benefit.

Obese women are more likely to give birth to an infant with certain congenital anomalies; the most frequent are NTDs. The risk of an NTD is double that compared to normal-weight women,⁶ and this association persists after controlling for diabetes as a potential confounding factor. Folic acid administration in doses higher than the usual recommended 400 μg daily has not been studied in women without diabetes, and whether this would confer any reduction in risk of NTDs in obese women is not known.

Other congenital defects are noted with increased frequency in obese women, and in decreasing order are congenital cardiac defects; orofacial defects, including cleft lip, cleft lip and palate, but not cleft palate alone; and limb abnormalities.⁷ The mechanism for the development of these types of defects and how they relate to obesity are not known.

An important factor in preconception counseling is to inform patients of potential lifelong implications in their offspring related to maternal obesity. The relationship between maternal obesity and diabetes in later life in both mothers and offspring is already well established.⁸ The exact cause of this relationship is not completely understood, and there may be multiple factors involved in the development of this relationship. There is certainly a strong genetic component, and a family history of type 1 and type 2 diabetes will significantly increase the rates of diabetes in progeny within these families. However, there also appears to be mechanisms, such as epigenetic modification of the fetal genome, that increase the rates of diabetes even in those without a family history of diabetes.

A 2012 study⁹ reported higher rates of impaired glucose tolerance of offspring in 21% of Caucasian women with gestational diabetes and 11% in Caucasian women with type 1 diabetes. These studies have shown impaired glucose tolerance that persists through at least 16 years of age, and other studies have found this association much later in life.¹⁰ There is a correlation with fetal hyperinsulinemia that leads to pancreatic overgrowth; excessive fat formation, leading to chronic inflammation; and development of metabolic syndrome. These correlations vary in degree of risk but are seen in age- and sex-matched controls across many populations and ethnicities. This risk remains unchanged after adjustment for demographic variables, socioeconomic status, and maternal prepregnancy BMI among populations studied.

The pathophysiology of the association between stillbirth and obesity is not entirely certain, but there may be several mechanisms involved. These include placental dysfunction, placental inflammation, impaired glucose tolerance and fetal insulin resistance, and hyperlipidemia. In many animal models, there are mechanisms that are known as programming effects. These are mechanisms by which an exposure to an outside agent or condition will activate certain genes within the genome, such that development of disease may occur. For example, the genes that control low-density lipoprotein (LDL) metabolism become activated.⁸ This may occur in utero, and offspring show cholesterol streaks within large vessels such as the aorta, renal arteries, and mesenteric arteries. These high-density LDL molecules are strong producers of vascular atherosclerotic plaques, and even though most will recede in newborns and children, there is increasing evidence⁸ that in utero, these genes confer a lifelong risk for the development of atherosclerotic disease.

Placental dysfunction has been shown in primates that are fed a high-fat diet. The obese primates being studied demonstrated an increased rate of placental insufficiency and increased stillbirth.¹¹ Pregnancy induces a pro-inflammatory, hyperlipidemic, insulin-resistant state, and these responses are exaggerated in obese women. These women will exhibit abnormal vascular function and changes to inflammatory mediators that lead to placental inflammation. This inflammation exacerbates insulin resistance and leads to fetal overgrowth, as insulin is the primary growth hormone in the fetus. These inflammatory and vascular changes are also seen within the placenta and will interfere with nutrient and metabolic waste exchange and cause atherosclerotic changes in the placental and fetal vasculature. The inflammation and atherosclerosis in vessels may contribute to the increased rate of stillbirth in pregnancies complicated by maternal obesity.

There is a national movement to decrease maternal morbidity and mortality, both antepartum and postpartum, in the United States. The program designed to decrease these risks is being piloted in New York as the Safe Motherhood Initiative and is supported by the American Congress of Obstetricians and Gynecologists. This program, which is being promoted in almost every hospital in New York that provides maternity care, will be implementing best practices in obstetrical care to screen for, prevent, and treat postpartum hemorrhage, severe hypertension, and venous thromboembolism. Obesity confers a higher risk of all of these maternal complications, and the implementation of these safety bundles is a critical and timely way to minimize pregnancy complications given the rising rates of maternal obesity. Discussion of these risks prior to conception and early in pregnancy allows the patient to understand the issues that may arise in a pregnancy, including embolic phenomena and anesthesia concerns.

Obesity increases the risk of venous thromboembolism, particularly around delivery and for 6 weeks postpartum. If an obese woman has additional risk factors, then antepartum thromboprophylaxis should be used and continued for 6 weeks postpartum. Whether prophylactic versus therapeutic dosing of thromboprophylaxis is used should be based on existing guidelines. All obese patients undergoing cesarean section should have thromboprophylaxis with sequential pneumatic compression devices at a minimum, and these should be continued until the patient is ambulatory.

Anesthesia poses a significant challenge for some patients, and an antepartum consultation with the anesthesia service is suggested. These patients often have difficult airways, and intubation in an emergent situation is a potential complication. They may have excessive soft tissue around their airways, and full extension of the neck may pose difficulties. In addition, swelling of the mucous membranes is normal during pregnancy, and this may pose yet another challenge when trying to secure the airway. Ideally, this evaluation will be considered early in pregnancy.

Ventilatory support can also be a particular issue, particularly in patients with class III obesity. Some obese women may have pendulous breast tissue, and further breast enlargement and engorgement occurs during the last half of pregnancy. When lying supine, this large volume of breast tissue may place significant weight onto the chest wall and increase chest and airway pressures. Some ventilation machines may not be able to generate enough air pressure and will subsequently “pop off” and stop the ventilatory cycle. Our anesthesia colleagues will also need to account for the increased volume of distribution in large patients and compensate for certain anesthetics that may be used. Some inhaled anesthetic agents are fat stored, and this will also need to be taken into account with prolonged periods of inhaled anesthesia. This may prolong the time necessary to wean a patient off the ventilator and safely extubate.

Careful determination of maternal weight is also necessary when planning for admission, as standard operating room tables may not be able to support of some of these women, and a bariatric operating table may needed. Large beds and wheelchairs may also be necessary for some patients with class II or III obesity, and prearrangements should be made. Prelabor planning is essential for these patients to ensure necessary equipment is available and so that any extra personnel are available if needed. Induction of labor at term may be considered in certain extreme circumstances to ensure a controlled environment in which all personnel and equipment are readily available.

Regional analgesia and anesthesia are recommended for these patients. This is often problematic due to obscured landmarks, difficulty in patient positioning, and excessive layers of adipose tissue. The last issue may necessitate using special instruments, including extra-long spinal needles to reach the epidural or intrathecal space. Ultrasound guidance may also be used to help proper placement of the needle during anesthesia administration.