Obesity and the risk and detection of fetal malformations

Abstract

The incidence of obesity in pregnancy has increased over the past 2 decades, with nearly 50% of U.S. women aged 15-49 years classified as overweight or obese. Obesity (independent of diabetes) among gravidae poses unique risks that extend toward the fetus, with several large population-based analyses demonstrating independent increased risks for fetal malformations including neural tube defects, cardiac anomalies, and orofacial clefts, as well as stillbirth and macrosomia. Unfortunately, several lines of evidence also suggest that the quality of the prenatal fetal anatomic survey and certain aspects of prenatal diagnostic screening programs are significantly limited. The net effect is that among obese gravidae, the increased risk of fetal anomalies is further offset by a concomitant diminished ability to sonographically detect such malformations in the prenatal interval. The purpose of this summary review is to systematically examine the evidence suggesting an increased risk of fetal malformations in obese gravidae, the contributing role of diabetes, and the limitations of prenatal diagnostic and sonographic screening among this at-risk population.

Figure 1. Prevalence of obesity among racial and ethnic groups among gravidae

As delineated in the text, the near majority of self-identifying Black or African-American women manifest obesity in pregnancy. A significant and growing minority of both Hispanic-ethnicity and Caucasian women similarly present in pregnancy as obese (20, 21).

Figure 2. Maternal obesity linearly increases the risk of being diagnosed with (or developing) gestational diabetes

The odds ratios for the diagnosis (or likely development) of gestational diabetes significantly and linearly increases with each IOM obesity classification, with the highest risk among morbidly obese (BMI >35 kg/m2) gravidae. These values are primarily compiled from references – and .

Figure 3. Differential capacity for visualization of fetal structures and markers of aneuploidy in normal weight (BMI <25 kg/m2) and obese women (BMI >35 kg/m2)

As demonstrated in multiple studies (–19, 54) and visualized herein, maternal obesity decreases the practitioner’s ability to confidently recognize such markers, or accurately assess their dimensions. For example, from the representative images in obese women, please note the poor delineation of the boarders of the lateral ventricles and renal pelvis (which may lead to inaccurate assessment), alongside the decreased echogenicity of the intracardiac echogenic focus (which may lead to missed diagnosis).