From the Guidelines
The recommended Rho(D) immune globulin (RhIG) dose is 50 mg for pregnancies less than 12 weeks of gestation, as indicated by the most recent guidelines. This dose is considered adequate to cover the volume of potential feto-maternal hemorrhage in the first trimester 1. The American Journal of Obstetrics and Gynecology recommends this lower dose to decrease the concern for resource over-utilization with RhIg administration. When the 50 mg dose is unavailable, a 300 mg RhIg dose may be used as an alternative. It is essential to note that the priority for RhIg administration should be given to postpartum patients and antenatal patients at later gestational ages when the supply of RhIg is limited 1. Some key points to consider when administering RhIG include:
- The dose of 50 mg is sufficient for the first 12 weeks of gestation
- A 300 mg dose may be used if the 50 mg dose is not available
- Priority should be given to postpartum patients and antenatal patients at later gestational ages when the supply of RhIg is limited
- Equivalent RhIg products may be substituted if the typically used brand is not available 1.
From the FDA Drug Label
For antenatal prophylaxis, one full dose syringe of HyperRHO S/D Full Dose (1500 IU; 300 mcg) is administered at approximately 28 weeks’ gestation. If abdominal trauma, amniocentesis, or other adverse event requires the administration of HyperRHO S/D Full Dose (1500 IU; 300 mcg) at 13 to 18 weeks’ gestation, another full dose should be given at 26 to 28 weeks
The recommended Rho(D) immune globulin (RhIG) dose is 1500 IU (300 mcg), administered as follows:
- At approximately 28 weeks’ gestation for antenatal prophylaxis
- An additional dose may be given at 26 to 28 weeks if an adverse event occurs at 13 to 18 weeks’ gestation 2
From the Research
Rho(D) Immune Globulin (RhIG) Dose Recommendations
The recommended Rho(D) immune globulin (RhIG) dose varies based on the weeks of gestation and the specific clinical scenario. The following are some general guidelines:
- At 28 weeks' gestation, a dose of 300 microg of RhIG is recommended for all Rh-negative nonsensitized women when the fetal blood type is unknown or known to be Rh-positive 3.
- Alternatively, two doses of 100-120 microg may be given, one at 28 weeks and one at 34 weeks 3.
- For events that may cause fetomaternal hemorrhage (FMH), such as amniocentesis, cordocentesis, or abdominal trauma, a dose of 300 microg of RhIG is recommended 4, 5.
- If the amount of fetal erythrocytes that entered the maternal circulation is quantitatively determined, administration of 10 microg of RhIG per 0.5 mL of fetal erythrocytes or 1 mL of whole fetal blood is indicated 4, 5.
- In cases where prevention of RhD alloimmunization is not performed within 72 hours of a potentially sensitizing event, it is still reasonable to administer RhIG within 13 days, and in special cases, administration is still recommended up to a maximum interval of 28 days postpartum 4, 5.
Specific Clinical Scenarios
Some specific clinical scenarios and their corresponding RhIG dose recommendations are:
- Termination of pregnancy, spontaneous abortion, or ectopic pregnancy: 50 microg of RhIG before 20 weeks' gestation, and 100 microg after 20 weeks' gestation 4, 5.
- Amniocentesis, cordocentesis, or other invasive prenatal diagnostic or therapeutic procedures: 100 microg of RhIG 4, 5.
- Delivery of an RhD positive infant: 100 microg of RhIG 4, 5, or 300 microg of RhIG within the first 72 hours postpartum 6.
- Cesarean section or twin delivery: the same dose as after a vaginal delivery, 300 microg of RhIG 6.