WinRho Postpartum Dosing After 28-Week Antenatal Prophylaxis
For a primigravida at 36+4 weeks who received WinRho at 28 weeks, the next dose is due within 72 hours after delivery if the infant is Rh-positive. 1, 2
Standard Two-Dose Protocol
The American College of Obstetricians and Gynecologists recommends a two-dose protocol that has reduced RhD alloimmunization rates from 1.8% to between 0.1% and 0.2%: 1
- First dose: 300 μg (1500 IU) at 28 weeks gestation 1, 2
- Second dose: 300 μg (1500 IU) within 72 hours after delivery if the infant is Rh-positive 1, 2
Critical Timing Considerations
The postpartum dose should be administered preferably within 72 hours of delivery, though it may still provide benefit if given up to 28 days after delivery. 3 Although protection decreases with delayed administration, late administration is still preferable to no administration at all. 4
When the Postpartum Dose May Be Withheld
If delivery occurs within 3 weeks after the 28-week dose (i.e., before 31 weeks gestation), the postpartum dose may be withheld UNLESS there is evidence of fetomaternal hemorrhage exceeding 15 mL of fetal red blood cells. 2
Since this patient is at 36+4 weeks, she is well beyond the 3-week window, so the postpartum dose is definitely required. 2
Dose Modification for Large Fetomaternal Hemorrhage
One standard 300 μg dose provides sufficient antibody coverage for up to 15 mL of fetal red blood cells (approximately 30 mL of whole fetal blood). 2, 3
If a large fetomaternal hemorrhage is suspected at delivery: 2, 3
- Perform quantitative testing using an approved laboratory technique (e.g., modified Kleihauer-Betke acid elution stain) 2
- Calculate additional doses needed: divide the red blood cell volume by 15 mL 2
- If the calculation results in a fraction, round up to the next whole number of doses 2
- Administer 10 μg additional anti-D for every additional 0.5 mL of fetal red blood cells beyond 15 mL 3
Common Pitfalls to Avoid
Do not assume the 28-week dose provides adequate coverage through delivery and postpartum. The half-life of IgG is 23 to 26 days, and protection must be maintained throughout pregnancy and reinforced after delivery. 2 The antenatal dose at 28 weeks reduces but does not eliminate the need for postpartum prophylaxis. 1
Do not delay postpartum administration while waiting for infant blood typing if there will be any delay beyond 72 hours. While determining the infant's Rh status is important, the 72-hour window is critical for optimal protection. 2, 3
Always confirm the infant's RhD phenotype even if fetal RhD genotyping was performed during pregnancy. 5 The postpartum dose is only necessary if the infant is confirmed Rh-positive. 1, 2