••• Chapter 20^ Rh Alloimmunization^211
❍ How often are MCA Dopplers performed during at-risk or affected pregnancies?
Weekly.
❍ After what gestational age, do MCA Dopplers have a higher false-positive rate?
34 to 35 weeks.
❍ How is amniotic fluid analysis used to estimate the degree of fetal red cell hemolysis?
Bilirubin causes a shift in spectrophotometric density of the amniotic fluid, and the amount of shift from 450 nm
(the ΔOD 450 ) is used to estimate the degree of fetal red cell hemolysis. The ΔOD 450 value is plotted on a Liley curve
(in the second and third trimesters) or a Queenan curve (early pregnancy). The Queenan curve has largely replaced
use of the Liley curve at all gestational ages. It is useful to follow the trend of these results.
❍ If fetal hydrops is detected on an ultrasound, how low is the fetal hematocrit?
Probably <15%.
❍ The Liley curve is divided into how many zones?
Three zones.
❍ What does each zone of the Liley curve indicate?
Zone I usually indicates mildly affected or unaffected fetus with a low risk of severe anemia.
Zone 2 indicates mild to moderate fetal hemolysis but low risk of severe anemia.
Zone 3 indicates severe anemia with high risk of fetal death within 7 to 10 days.
Lower zone expected hemoglobin is 11.0 to 13.9 g/dL; upper zone expected hemoglobin is 8.0 to 10.9 g/dL.
❍ Amniocentesis is performed and demonstrates results in Zone 1. When would the next amniocentesis be
repeated?
Every 10 days to 2 weeks.
❍ When describing the Liley curve, in addition to zones, what other information is needed to properly plot an
amniocentesis result?
Gestational age. The Liley curve is gestational age specific.
❍ In a preterm fetus with a value in Liley Zone 3, management would include what?
Fetal blood sampling and intrauterine transfusion.
❍ What is the proper management of a fetus with severe Rh sensitization and absent lung maturity at 30 to
32 weeks’ gestation?
Controversial, but because of excellent outcomes with current neonatal intensive care, transfusion, and maternal
steroid administration with delivery at 32 to 34 weeks may be considered.
❍ What is the proper management of mild fetal hemolysis and reassuring fetal testing?
Delivery at 37 to 38 weeks’ gestation or earlier if fetal lung maturity documented.