Clinical Review

Obesity in pregnancy: Risks and interventions by gestational stage

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Gestational diabetes, preeclampsia, prolonged hospitalization—these are just a few of the complications that may affect obese gravidas. Here, the authors present a rundown of what to look for when treating this unique population.


 

References

KEY POINTS
  • All obese patients have an increased risk of gestational diabetes and preeclampsia.
  • Deep venous thrombosis and its complications—which include maternal mortality—are seen more frequently in the obese patient.
  • Obesity is associated with an increased likelihood of induction of labor and cesarean delivery.
  • Obesity is a specific risk factor for several operative complications, including hemorrhage during surgery, postoperative wound infections, aspiration, and pulmonary embolism.
Specific interventions can help reduce the complications associated with obesity in pregnancy, provided physicians remain vigilant in applying the appropriate preventive measures.

Since one third of American women of childbearing age are overweight, obesity clearly has a major impact on the health of pregnant patients. And, as in the general population, the prevalence of this condition is escalating among gravidas. A 2001 study cited a 20% increase in mean maternal weights between 1980 and 1999.1

In the United States, the prevalence of obesity leaped from 12% to 17.9% between 1991 and 1998.2 Even more alarmingly, each year in this country, 280,000 adult deaths are attributable to obesity.

As health-care providers, it is imperative that we understand the impact this epidemic has on pregnancy and delivery so that we can work to minimize related complications.

What is obesity?

There is no single definition of obesity. In obstetric literature, it has been defined as a maternal weight of more than 90 kg (200 lb), more than 114 kg (250 lb), more than 135 kg (300 lb), and anywhere from 50% to 120% above ideal body weight.

In recent years, clinicians have usually determined obesity according to the body mass index (BMI), a simple mathematical formula (weight in kilograms divided by height in square meters) that correlates height and weight with body fat. This method offers several advantages over a basic weight measurement. For one, weight alone does not correlate well with body fat content; BMI, on the other hand, has a 0.7 to 0.8 correlation. In addition, this definition of obesity correlates with morbidity and mortality.3

Using BMI, the Institute of Medicine developed 4 body-type categories4:

  • under 19.8: lean
  • 19.8 to 26.0: normal
  • 26.1 to 29: overweight
  • over 29: obese
In obstetric patients, BMI is calculated using prepregnancy weight. While the varying definitions of obesity make it difficult to compare and interpret research findings, it is important to note that adverse obstetric outcomes are associated with each classification. The Institute of Medicine also made recommendations on how much weight women in each category should gain during pregnancy5:
  • lean women: 28 lb to 40 lb
  • normal-weight women: 25 lb to 35 lb
  • overweight women: 15 lb to 25 lb
  • obese women: 15 lb or more
While no upper weight-gain limit was set for obese patients, 3 studies recommend 37 lb; researchers found that obese women who gain more than this have increased risk of cesarean delivery and large-for-gestational-age infants.6-8

Preconception: Control hypertension and diabetes

The negative impact that excess weight has on pregnancy begins even before conception (TABLE 1). For example, obese women are more likely to have chronic hypertension and diabetes. In 1 study, researchers reported the incidence of chronic hypertension among obese patients (defined as those weighing 300 lb or more) to be 33%, compared with 5% among controls, while diabetes occurred in 15% of obese patients and 3% of controls.9

Through preconception counseling and management, practitioners can improve pregnancy outcomes among patients with these medical complications. Strict glucose control of pregestational diabetes, for example, decreases the risk of congenital malformations. The 4-fold increase in malformations related to poor glucose control during embryogenesis is diminished if preconceptional glycosylated hemoglobin levels are in the normal range.10

Note that hypertension may be falsely diagnosed in an obese woman if an inappropriately small cuff is used. When taking the blood pressure (BP) of these patients, therefore, clinicians should make sure the length of the cuff is 1.5 times the upper arm circumference or that the inflatable bladder of the cuff encircles at least 80% of the arm.11 For women with an arm circumference of more than 41 cm, use a thigh cuff to ensure an accurate measurement.

In general, any hypertensive woman of childbearing age should take only agents with documented fetal safety. Drugs such as angiotensin-converting enzyme inhibitors should not be used due to their association with oligohydramnios, fetal hypocalvaria, and neonatal renal failure.

TABLE 1

Obstetric concerns among obese patients

PreconceptionPregestational diabetes mellitus
Chronic hypertension
Antepartum periodGestational diabetes
Preeclampsia
Deep venous thrombosis
Stillbirth
Intrapartum periodInduction
Cesarean delivery
Poor VBAC success
Macrosomia
Postpartum periodProlonged hospitalization
Cesarean complications
Wound infection
VBAC = vaginal birth after cesarean

Antepartum

Gestational diabetes and preeclampsia. During pregnancy, all obese patients—even those without a history of hypertension or diabetes—have an increased risk of gestational diabetes and preeclampsia. Baeten et al12 recently reported the odds ratios for gestational diabetes, preeclampsia, and eclampsia in the obese nulliparous patient as 5.2, 3.3, and 3.0, respectively.

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