High BMI Lowers Detection of Fetal Abnormalities


CHICAGO — High maternal body mass index decreases the ability to detect fetal abnormalities with standard or targeted second-trimester ultrasound, a retrospective study of more than 10,000 examinations has shown.

The study found a significant decrease in detection of anomalous fetuses with increasing body mass index (BMI) with standard ultrasound and also when standard and targeted ultrasound were combined.

“Counseling may need to be modified to reflect the limitations of sonography in the setting of obesity,” Dr. Jodi S. Dashe of the University of Texas at Dallas reported at the World Congress on Ultrasound in Obstetrics and Gynecology.

“It may be harder to identify fetal anomalies in obese women because the ultrasound transducer is farther from the fetus, which limits the image resolution,” Dr. Dashe commented in an interview.

In the present study, researchers reviewed pregnancies that received standard or targeted ultrasound between 18 and 24 weeks of gestation and were delivered at the University of Texas Southwestern Medical Center between 2003 and 2007.

Standard ultrasound had been done in keeping with the criteria of the American Institute of Ultrasound in Medicine. Targeted ultrasound was performed for specific high-risk indications.

The researchers included all potentially life-threatening structural abnormalities in their analysis as well as those requiring surgery, even if detection of the anomaly would not be expected with ultrasound. Researchers used a prospectively kept database of birth defects to verify ultrasound-detected anomalies.

An anomalous fetus was considered detected if an abnormality of the relevant organ system was identified. The researchers used patients' BMIs at first prenatal visit in their analysis, categorizing BMI according to National Institutes of Health criteria: normal (less than 25 kg/m

Of 10,112 standard and 1,023 targeted ultrasound examinations, anomalies were verified in 181 infants (1.6%).

Standard ultrasound detected 66% of anomalous fetuses in women with a normal BMI, but only 49%, 48%, 42%, and 25% of anomalous fetuses in women in the overweight and class I, II, and III obesity categories, respectively.

The combined detection of anomalous fetuses was 68% in women with a normal BMI but only 55%, 49%, 47%, and 43% in women in the overweight and class I, II, and III obesity categories.

Previous research on fetal cardiac visualization and BMI also found significantly higher rates of persistent suboptimal ultrasonographic visualization (SUV) on a repeated ultrasound examination in obese women, compared with nonobese women.

SUV rates increased with increasing BMI in obese patients (J. Ultrasound Med. 2005;24:1205-9).

Dr. Dashe said she and her colleagues hope to do further research in this area. She had no financial conflicts of interest to report.

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