How should a Rh‑negative pregnant woman be managed with respect to Rh immunoglobulin prophylaxis and antibody screening?

Management of Rh-Negative Pregnancy

All Rh-negative pregnant women should receive routine antenatal Rh immunoglobulin (RhIg) prophylaxis at 28 weeks of gestation and again within 72 hours postpartum if the neonate is Rh-positive, with additional doses required after any potentially sensitizing event throughout pregnancy. 1

Initial Assessment and Antibody Screening

• Perform initial antibody screening at the first prenatal visit to identify women who are already sensitized to RhD or other red blood cell antigens. 1

• Repeat antibody screening at approximately 24-28 weeks gestation in unsensitized Rh-negative women before administering antenatal prophylaxis. 2

• If antibodies are detected, the pregnancy requires specialized management for alloimmunization, including cell-free fetal DNA testing to determine fetal antigen status and middle cerebral artery Doppler surveillance for fetal anemia. 1

Routine Antenatal Prophylaxis

Standard dosing and timing:

• Administer 300 mcg of RhIg at 28 weeks of gestation to all unsensitized Rh-negative women. 1, 3

• This single dose at 28 weeks is the standard approach, though evidence shows that nearly two-thirds of women will have undetectable anti-D antibodies at term if delivery occurs more than 10 weeks after administration. 2

• Consider noninvasive fetal RHD genotyping using cell-free DNA from maternal plasma starting at 18-20 weeks gestation to identify women carrying Rh-negative fetuses who do not require prophylaxis. 1, 4, 5

• Fetal RHD screening demonstrates ≥99.9% diagnostic sensitivity and can avoid unnecessary prophylaxis in 36-40% of Rh-negative pregnant women carrying Rh-negative fetuses. 4, 5

Postpartum Prophylaxis

• Administer 300 mcg RhIg within 72 hours of delivery if the neonate is confirmed to be Rh-positive. 3

• While administration within 3 hours is ideal, RhIg remains effective up to 72 hours post-exposure and should still be considered even if this window is exceeded. 3

• If the infant's Rh status cannot be determined, assume the infant is Rh-positive and administer prophylaxis. 3

Prophylaxis for Potentially Sensitizing Events

First trimester events (≤12 weeks gestation):

• For spontaneous or induced abortion at <12 weeks, administer 50 mcg (mini-dose) RhIg within 72 hours when RhD testing and RhIg are logistically and financially feasible. 6, 3

• If the 50 mcg dose is unavailable, a standard 300 mcg dose is acceptable. 6

• While the risk of alloimmunization from first-trimester events is low, it is not negligible at the population level, and the consequences of sensitization are severe. 6

• In settings where requiring RhD testing or RhIg would delay or create barriers to abortion access, prioritize completing the abortion and counsel patients on the potential implications of unknown blood type. 6

After 12 weeks gestation:

• For any abortion or miscarriage occurring after 12 weeks, administer the standard 300 mcg dose of RhIg. 3

Other sensitizing events requiring 300 mcg RhIg:

• Invasive procedures (amniocentesis, chorionic villus sampling, cordocentesis) 7, 8
• Abdominal trauma during pregnancy 7, 8
• External cephalic version 7
• Vaginal bleeding during pregnancy 8
• Ectopic pregnancy 7
• Molar pregnancy 7

Management of Already Sensitized Pregnancies

If a woman is already sensitized (positive antibody screen):

• Use cell-free fetal DNA testing early in pregnancy to determine if the fetus carries the relevant antigen. 1

• Implement middle cerebral artery peak systolic velocity Doppler measurements starting earlier in pregnancy to detect fetal anemia. 1

• Consider intravenous immune globulin (IVIG) in select high-risk cases: specifically in women with a documented antigen-positive fetus and a history of either fetal anemia or fetal loss due to hemolytic disease before 24 weeks in a previous pregnancy. 1

• If intrauterine transfusion is required, continue therapy until 35 weeks gestation. 1

• Plan delivery between 37 weeks 0 days and 38 weeks 6 days in alloimmunized pregnancies. 1

Common Pitfalls to Avoid

• Failure to administer RhIg after sensitizing events: Despite comprehensive prophylaxis programs, allo-anti-D remains the most common cause of severe hemolytic disease of the fetus and newborn, often due to missed doses after unrecognized sensitizing events. 8

• Assuming all Rh-negative women need prophylaxis: Implementing fetal RHD genotyping can avoid unnecessary exposure to blood products in over one-third of women carrying Rh-negative fetuses. 4, 5

• Delaying postpartum prophylaxis: The effectiveness of RhIg decreases with time; aim for administration within 3 hours when possible, though up to 72 hours remains beneficial. 3

• Inadequate dosing for first-trimester events: While 50 mcg is adequate for events ≤12 weeks, events after 12 weeks require the full 300 mcg dose. 3