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Obstetrics & Gynecology 2008;111:1083-1088
© 2008 by The American College of Obstetricians and Gynecologists
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ORIGINAL RESEARCH

Bilirubin/Albumin Ratios in Fetal Blood and in Amniotic Fluid in Rhesus Immunization

Suzanne A. Pasman, MD1, Esther Sikkel, MD, PhD1, Saskia Le Cessie, PhD2, Dick Oepkes, MD, PhD1, Freek W. C. Roelandse3 and Frank P. H. A. Vandenbussche, MD, PhD1

From the Departments of 1Obstetrics, 2Medical Statistics, and 3Clinical Chemistry, Leiden University Medical Centre, Leiden, the Netherlands.

OBJECTIVE: To test the hypothesis that unconjugated bilirubin is equally distributed over the albumin molecules present in fetal blood and amniotic fluid in Rhesus (Rh) immunization.

METHODS: Molar concentrations of unconjugated bilirubin and albumin were measured in fetal blood and amniotic fluid samples, obtained before the first intrauterine transfusion in 30 nonhydropic, anti-D–alloimmunized fetuses, with gestational ages ranging from 20 to 35 weeks.

RESULTS: Bilirubin concentration in amniotic fluid was best predicted by a combination of bilirubin concentration in fetal blood (P<.001), albumin concentration in fetal blood (P=.008), and albumin concentration in amniotic fluid (P<.001) (adjusted R2=0.91). The bilirubin/albumin ratios in fetal blood were linearly correlated with the bilirubin/albumin ratios in amniotic fluid (R2=0.75, P<.001). However, the bilirubin/albumin ratios in fetal blood were always higher than the bilirubin/albumin ratios in amniotic fluid (regression coefficient 1.4, 95% confidence interval 1.1–1.7). In our population, a bilirubin/albumin ratio in amniotic fluid of 0.10 or greater had a better sensitivity and specificity to predict severe anemia (Z hemoglobin –5 standard deviations or less) than the Queenan 4 or the Liley 2c line.

CONCLUSION: The relation between fetal hemolysis and amniotic fluid bilirubin concentration is based on the linear correlation between bilirubin/albumin ratios in fetal blood and in amniotic fluid. The slope in Queenan’s and Liley’s chart follows that of the albumin concentration in amniotic fluid during gestation.

LEVEL OF EVIDENCE: III






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