RhoGAM at 32 Weeks Gestation
Yes, RhoGAM remains highly beneficial at 32 weeks gestation for an Rh-negative pregnant woman, and should absolutely be administered if the standard 28-week dose was missed.
Standard Timing and Rationale
The American College of Obstetricians and Gynecologists recommends routine RhIg prophylaxis at 28 weeks gestation, with a postpartum dose within 72 hours after delivery of an Rh-positive infant 1. This two-dose protocol reduces RhD alloimmunization rates from approximately 1.8% to between 0.1% and 0.2% 1. The mechanism works by suppressing the maternal immune response to fetal Rh-positive red blood cells, though the complete mechanism is not fully understood 2.
Why 32 Weeks Still Provides Protection
Fetal RBC exposure occurs throughout pregnancy: Fetal red blood cells display RhD antigens from as early as 6 weeks gestation, making maternal sensitization possible at any point during pregnancy 1.
Late pregnancy carries significant risk: The 1-2% treatment failures with postpartum-only RhIg are primarily due to isoimmunization occurring during the latter part of pregnancy or following delivery 2. This underscores that third-trimester exposure is a critical window for sensitization.
Delayed administration is better than none: While RhIg should preferably be given within 72 hours of a sensitizing event, it may still provide benefit if given up to 28 days later, as delayed administration decreases protection but is still preferable to no administration at all 1.
Clinical Algorithm for 32-Week Administration
If the 28-week dose was missed:
- Administer 300 μg RhIg immediately at 32 weeks 1, 2
- Still plan for postpartum dose within 72 hours of delivery if infant is Rh-positive 1
- The antenatal dose at 32 weeks will provide protection for the remaining 8 weeks of pregnancy
Priority during shortages:
- If RhIg supply is limited, postpartum patients and antenatal patients at later gestational ages (like 32 weeks) should be prioritized 1
Critical Pitfalls to Avoid
Don't assume it's "too late": The window between 28-40 weeks represents a high-risk period for fetomaternal hemorrhage, and protection during these final weeks is essential 1, 2.
Don't skip the postpartum dose: Even if RhIg is given at 32 weeks, the postpartum dose is still required if the infant is Rh-positive, as the antenatal dose may not provide complete coverage through delivery and the immediate postpartum period 1.
Consider additional dosing for trauma: If there has been any placental trauma, abdominal trauma, or bleeding between 32 weeks and delivery, quantitative testing for fetomaternal hemorrhage should be considered to determine if additional doses are needed 1, 3.
Dosing Specifics
The standard dose is 300 μg (1500 IU) administered intramuscularly or intravenously 2, 3. Both routes are equally effective, with similar anti-D IgG concentrations from 2-3 weeks post-administration onward 4.