Amniotic fluid is evaluated using a Liley graph and change in absorbance of 450 nm. What is being evaluated and why?

Amniotic fluid is evaluated using a Liley graph and change in absorbance of 450 nm. What is being evaluated and why?

• A. Bilirubin, which increases in HDN
• B. AFP, which increases in spina bifida
• C. hCG, which increases in Down syndrome
• D. Lamellar bodies, increase with fetal lung maturity

Answer: (A)

The test is about bilirubin in amniotic fluid and how its level reflects fetal hemolysis. In hemolytic disease of the fetus and newborn, red blood cell destruction raises unconjugated bilirubin, which diffuses into the amniotic fluid. This bilirubin has a peak absorbance near 450 nm, so photometrically measuring the change in absorbance at 450 nm (delta OD450) provides a quantitative estimate of amniotic fluid bilirubin. The Liley graph plots this bilirubin value against gestational age to categorize risk into zones, guiding management from close monitoring to intrauterine transfusion or early delivery. The other options describe markers tied to different conditions (AFP for neural tube defects, hCG for Down syndrome, lamellar bodies for fetal lung maturity) and are not assessed by the 450 nm bilirubin measurement.

The test is about bilirubin in amniotic fluid and how its level reflects fetal hemolysis. In hemolytic disease of the fetus and newborn, red blood cell destruction raises unconjugated bilirubin, which diffuses into the amniotic fluid. This bilirubin has a peak absorbance near 450 nm, so photometrically measuring the change in absorbance at 450 nm (delta OD450) provides a quantitative estimate of amniotic fluid bilirubin. The Liley graph plots this bilirubin value against gestational age to categorize risk into zones, guiding management from close monitoring to intrauterine transfusion or early delivery. The other options describe markers tied to different conditions (AFP for neural tube defects, hCG for Down syndrome, lamellar bodies for fetal lung maturity) and are not assessed by the 450 nm bilirubin measurement.