What is the Rh immune globulin (RhIg) dose based on weeks of gestation?

From the Guidelines

The recommended dose of Rh immune globulin (RhIg) is 50 mg for pregnancies less than 12 weeks of gestation, as indicated by the most recent guidelines 1. When considering the administration of RhIg, it is essential to take into account the weeks of gestation to determine the appropriate dose.

• For pregnancies less than 12 weeks of gestation, a 50 mg dose of RhIg is recommended to cover the volume of potential feto-maternal hemorrhage in the first trimester 1.
• If the 50 mg dose is unavailable, a 300 mg dose of RhIg may be administered as an alternative 1. 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. Key points to consider when administering RhIg include:
• The dose of RhIg should be administered within 72 hours of the spontaneous or induced abortion 1.
• If a typically used brand of RhIg is not available, an equivalent RhIg product may be substituted if 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. Following 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 Rh immune globulin (RhIg) dose is 1500 IU; 300 mcg at approximately 28 weeks’ gestation for antenatal prophylaxis.
• If an adverse event occurs at 13 to 18 weeks’ gestation, a dose of 1500 IU; 300 mcg is given, and another dose of 1500 IU; 300 mcg should be given at 26 to 28 weeks.
• No specific dose is provided based on weeks of gestation for other situations, such as postpartum prophylaxis or fetomaternal hemorrhage, except that a dose may be given at 26 to 28 weeks if an event occurred earlier in pregnancy 2.

From the Research

Rh Immune Globulin (RhIg) Dose Based on Weeks of Gestation

• The dose of RhIg varies based on the week of gestation and the specific clinical scenario 3, 4, 5, 6, 7
• At 28 weeks' gestation, a dose of 300 microg of RhIg is recommended for all Rh-negative nonsensitized women when fetal blood type is unknown or known to be Rh-positive 3
• Alternatively, 2 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, 6
• 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, 6

Specific Clinical Scenarios

• After miscarriage or threatened abortion or induced abortion during the first 12 weeks of gestation, a minimum dose of 120 microg of RhIg is recommended 3
• After 12 weeks' gestation, a dose of 300 microg of RhIg is recommended 3
• For ectopic pregnancy, a minimum dose of 120 microg of RhIg should be given before 12 weeks' gestation and 300 microg after 12 weeks' gestation 3
• For molar pregnancy, RhIg should be given to nonsensitized D-negative women because of the possibility of partial mole 3

Timing of RhIg Administration

• RhIg should be administered within 72 hours of delivery or other potentially sensitizing event 3, 4, 5, 6
• If RhIg is not given within 72 hours, it should be given as soon as the need is recognized, for up to 28 days after delivery or other potentially sensitizing event 3, 4, 5, 6