210 Obstetrics and Gynecology Board Review •••
❍ For which gestational events is Rh immune globulin indicated?
Fetomaternal hemorrhage with ectopic pregnancy or abortion, chorionic villus sampling, amniocentesis, external
cephalic version, significant antepartum bleeding, molar pregnancy (complete mole controversial), blunt
abdominal trauma, fetal death in the second or third trimester, or multifetal reduction.
❍ Is threatened abortion before 12 weeks’ gestation an indication for anti-D immune globulin prophylaxis?
Controversial. The RhD antigen has been reported on fetal erythrocytes as early as 38 days of gestation, but
alloimmunization rate is low in threatened abortions before 12 weeks.
❍ What dose of anti-D immune globulin, if indicated, should be given in the first trimester?
50 mg.
❍ At what anti-D antibody titer is a patient considered to be sensitized?
1: 4.
❍ It has been suggested that severe erythroblastosis or perinatal death does not occur when antibody levels
remain below a “critical titer.” What is this critical titer level?
1:16. This number may vary depending on the lab.
❍ In which situation is measuring maternal anti-D antibody titers not indicated?
If a previous affected pregnancy included severe fetal anemia (perinatal loss or intrauterine/neonatal transfusion).
In this situation, maternal antibody titers do not predict the degree of fetal anemia in the current pregnancy.
❍ If a mother has had a hydropic fetus, what is the recurrence risk?
80%.
❍ What is the initial management for a subsequent pregnancy following an affected fetus/infant?
First check the paternal genotype. If the father is a heterozygote, perform amniocentesis at 15 weeks’
gestation to determine fetus’ RhD status. If the fetus is RhD-negative, no further follow-up is needed. If the
fetus is RhD-positive or the father is a homozygote, begin serial middle cerebral artery (MCA) Dopplers or
amniocentesis (if Dopplers are not available) at 18 weeks.
❍ What noninvasive test is known to be the most accurate way to document fetal anemia in at-risk
pregnancies?
MCA Doppler studies.
❍ What are the sensitivity and specificity of MCA Doppler measurements?
Up to 90% sensitive and 98% specific.
❍ What MCA Doppler measurement corresponds with severe fetal anemia?
A MCA peak systolic velocity (PSV) >1.5 multiples of the median (MoMs).