Bilirubin/albumin ratios in fetal blood and in amniotic fluid in rhesus immunization.
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.


CONCLUSIONS
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.


METHODS
III.
Pasman
Suzanne A
SA
Departments of Obstetric, Leiden University Medical Centre, Leiden, the Netherlands. S.A.Pasman@LUMC.nl
Sikkel
Esther
E
Le Cessie
Saskia
S
Oepkes
Dick
D
Roelandse
Freek W C
FW
Vandenbussche
Frank P H A
FP
D000328:Adult; D000418:Albumins / Q000378:metabolism*; D000653:Amniotic Fluid / Q000737:chemistry*; D001663:Bilirubin / Q000378:metabolism*; D005260:Female; D005865:Gestational Age; D006801:Humans; D016014:Linear Models; D011247:Pregnancy; D012372:ROC Curve; D012203:Rh Isoimmunization / Q000097:blood / Q000378:metabolism*
D000418:Albumins; D001663:Bilirubin