WinRho Dosing for 28-Week Gestation Pregnancy with O- Blood Type and Negative Antibodies
For a 28-week gestation pregnancy with O- blood type and negative antibodies, the recommended dose of WinRho (Rho(D) immune globulin) is 300 μg (1500 IU) administered intramuscularly. 1, 2
Standard Antenatal Prophylaxis Protocol
- At 28 weeks gestation, Rh-negative pregnant women without antibodies should receive 300 μg (1500 IU) of Rho(D) immune globulin intramuscularly as routine prophylaxis 1
- This antenatal dose is a critical component of the two-dose protocol (28 weeks and postpartum) that reduces the rate of RhD alloimmunization from approximately 1.8% to between 0.1% and 0.2% 2
- The intramuscular route is preferred for administration, preferably in the deltoid muscle of the upper arm or lateral thigh muscle 1
- The gluteal region should be avoided as an injection site due to risk of sciatic nerve injury 1
Clinical Rationale
- Fetal red blood cells display RhD antigens from as early as 6 weeks of gestation, making maternal sensitization possible throughout pregnancy 2
- Studies show that fetomaternal hemorrhage occurs in 45% of women during the third trimester, which can lead to maternal sensitization if prophylaxis is not given 3
- The 28-week timing is optimal as approximately 90% of alloimmunization cases in primigravidae are detectable after 28 weeks' gestation 3
- Antenatal prophylaxis at 28 weeks provides protection against "silent" fetomaternal hemorrhage that may occur without clinical symptoms 3
Follow-up Dosing Requirements
- A second dose of 300 μg (1500 IU) should be administered within 72 hours after delivery if the infant is Rh-positive 1, 2
- If delivery occurs within 3 weeks after the 28-week dose, the postpartum dose may be withheld unless there is evidence of significant fetomaternal hemorrhage (>15 mL of fetal red blood cells) 1
- For significant fetomaternal hemorrhage (>15 mL of fetal red blood cells), additional doses may be required, calculated by dividing the red blood cell volume by 15 mL to determine the number of syringes needed 1
Special Considerations
- During the current WinRho shortage, pregnant women at 28 weeks gestation should still be prioritized for receiving available doses 4
- If the typically used brand of RhIg is not available, an equivalent RhIg product (e.g., HyperRHO S/D, Rhophylac) may be substituted 4
- The half-life of IgG is 23-26 days, so the 28-week dose provides protection through most of the third trimester 1
Important Caveats
- Never administer WinRho intravenously for routine antenatal prophylaxis - only use the intramuscular route 1
- Never administer the product to the neonate 1
- Verbal or written informed consent should be obtained prior to administration of Rho(D) immune globulin 5
- Women with "weak D" (Du-positive) should not receive anti-D prophylaxis 5
- For O- women with their first pregnancy, this prophylaxis is particularly important as it prevents sensitization that could affect future pregnancies 6, 7