NEW YORK (Reuters Health) – The ability to detect major fetal anomalies by ultrasonography is reduced in pregnant women who are obese or diabetic, according to researchers at the University of Texas Southwestern Medical Center in Dallas.
"It was our intention to evaluate whether fetuses with anomalies would come to attention, realizing that once an abnormality was recognized, additional specialized studies would be performed and neonatal intensive care unit personnel would be present at delivery if needed – neither of which would necessarily occur had an abnormality not been identified," Dr. Jodi S. Dashe and associates state in the May Obstetrics & Gynecology.
Their retrospective study included 11,135 singleton pregnancies in which ultrasonography was performed at 18 to 24 weeks. Body mass index as determined at the first prenatal visit was within the normal range in 39% of mothers; 34% were overweight and 27% were obese.
There were 181 infants born with anomalies. Detection of anomalous fetuses was 53% among women who underwent standard ultrasonography and 68% in those with high-risk indications who underwent a more targeted ultrasound examination by physicians with expertise in prenatal diagnosis of fetal anomalies.
Among patients who underwent standard ultrasound, the anomaly detection rate decreased with increasing BMI, from 66% in women with normal BMI to 48% in overweight women, and 48%, 42%, and 25% with class I, II, and III obesity, respectively (p for trend = 0.03).
Among those who had targeted ultrasonography, the difference in detection rates among groups did not reach significance, the authors note.
The residual anomaly risk, if none was noted on the initial ultrasound examination, increased from 0.4% among women with normal BMI to 1.0% among obese women (p for trend = 0.001); i.e., specificity decreased from 99.6% to 99%.
Diabetic women were far more affected, with a greater prevalence of anomalies and lower anomaly detection rate (approximately 4%) that was not associated with maternal BMI. ":It may be," Dr. Dashe and associates suggest, "that the predominantly truncal obesity that complicates diabetes may have played a role."
"Counseling may need to be modified to reflect the limitations of ultrasonography in obese women," they conclude.
Obstet Gynecol 2009;113:1001-1007.