Introduction

Obesity continues to be a major public health problem, affecting >30% of reproductive-age women in the United States . The incidence of morbid obesity (body mass index (BMI) >40 kg/m ² ) in reproductive-age women exceeds 7%, which is 50% higher than the rate in men in the same age group . Recent studies have shown that, when compared to normal-weight women, obese women have more pregnancy complications, such as congenital malformations , stillbirth , cesarean delivery , infection , preeclampsia, gestational diabetes, and macrosomic infants .

A meta-analysis of 18 articles noted that the rates of congenital anomalies are increased in obese women . When compared to normal-weight women, obese women had increased odds of neural tube defect (odds ratio (OR) 1.87, confidence interval (CI) 1.62–2.15), cardiovascular anomalies (OR 1.39, CI 1.03–1.87), cleft lip and palate (OR 1.20, CI 1.03–1.40), anorectal atresia (OR 1.48, CI 1.12–1.97), hydrocephaly (OR 1.68, CI 1.19–2.36), and limb reduction anomalies (OR 1.34, CI 1.03–1.73) . Prenatal ultrasound diagnosis of these anomalies can be challenging in obese women due to multiple factors. Obese women have increased depth of abdominal adipose tissue. This affects visualization due to the increased distance of insonation . Obese women have an increased risk of cesarean delivery compared to normal-weight women , and cesarean scars in subsequent pregnancies can affect the quality of the acoustic window. There is also evidence that obese women have increased rates of dizygotic twinning even without the influence of fertility drugs and ultrasound evaluation of multiple gestation presents additional challenges.

The purpose of this review is to provide an evidenced-based perspective on the challenges of performing fetal ultrasound in obese women and to provide a practical guide on how to care for these patients in the ultrasound suite. In this review, obesity is defined using the World Health Organization (WHO) BMI categories that include normal (18.5–24.9 kg/m ² ), overweight (25–29.9 kg/m ² ), and obese (≥30 mg/m ² ). Obesity is further separated into class I (30–34.9 kg/m ² ), class II (35–39.9 kg/m ² ), and class III (≥40 kg/m ² ). Class III obesity is also defined as morbid obesity.