RENO, NEV. — Middle cerebral artery Doppler ultrasonography has better sensitivity and specificity for detecting severe maternal red cell alloimmunization than amniotic fluid bilirubin values, Dick Oepkes, M.D., said at the annual meeting of the Society for Maternal-Fetal Medicine.
He and his associates conducted a study of 164 pregnancies, in which severe anemia occurred in 74. They found that ultrasonography can safely replace determination of the deflection of the optical density of amniotic fluid at 450 nm, said Dr. Oepkes, director of the fetal medicine section of the department of obstetrics at the Leiden University Medical Center, the Netherlands.
“The Doppler is clearly the superior technique,” he said. “The results of what we have found have confirmed what many people have directly implemented in their own centers already.”
The study's 164 pregnancies were in women who had serum antibody titers indicative of Rh positivity with antigen-positive fetuses. The women underwent amniocentesis and ultrasonography at the same time and then had fetal or cord blood sampling to confirm anemia, either at the time it was deemed necessary or at birth.
Severe anemia, which was confirmed in 74 neonates, was defined as a hemoglobin greater than or equal to 5 standard deviations from the mean for gestational age.
The sensitivity of the middle cerebral artery Doppler ultrasonography was 88%, and the specificity was 82%, yielding a positive predictive value of 80% and a negative predictive value of 89%.
In contrast, the amniotic fluid bilirubin (Delta-OD 450) values had a sensitivity of 76%, a specificity of 77%, a positive predictive value of 73%, and a negative predictive value of 80%.
The sensitivity of the Doppler was equally good, whether it was performed before or after 27 weeks' gestation, Dr. Oepkes explained.
Moreover, the study was conducted at 10 different institutions, and there was no great difference seen in the reliability of different ultrasonographers.
“We actually felt that this study was a pragmatic test that was done in the field so to speak,” Dr. Oepkes said.