What is RhoGAM used for?

RhoGAM (Rh immunoglobulin) prevents Rh sensitization in Rh-negative mothers who may have been exposed to Rh-positive fetal blood. Without it, the mother can develop antibodies that attack the red blood cells of a future Rh-positive baby, causing hemolytic disease of the newborn.

What is the standard RhoGAM dose?

The standard dose is 300 mcg (one vial), which protects against up to 30 mL of fetal whole blood (or 15 mL of fetal red blood cells). For larger exposures estimated by Kleihauer-Betke testing, additional vials are required.

What dose is used in early pregnancy (before 12 weeks)?

A mini-dose of 50 mcg is often sufficient for sensitizing events before 12 weeks gestation because fetal blood volume is small. However, the full 300 mcg dose can also be used if the mini-dose is unavailable.

How is the dose calculated after a large fetomaternal hemorrhage?

Use the Kleihauer-Betke result to estimate fetal whole-blood volume. Divide the volume in mL by 30, round to the nearest whole number, and add one additional 300 mcg vial for safety. Follow the institution’s transfusion-medicine protocol.

Within what timeframe must RhoGAM be given?

RhoGAM should be administered within 72 hours of the sensitizing event for maximum effectiveness. It can be given up to 28 days after exposure and may still confer partial protection.

Does this calculator replace clinical judgment?

No. This tool is for educational and reference purposes only. Dosing decisions must be made by a licensed healthcare provider who can consider the full clinical picture, institutional protocols, and patient-specific factors.

RhoGAM Dose Calculator

Calculate the correct RhoGAM (Rh immunoglobulin) dose for Rh-negative mothers based on gestational age and estimated fetal blood volume exposure.

Patient Parameters

Gestational Age (weeks)

Enter gestational age at time of event (4–42 weeks)

Indication

Dosing Recommendation

Enter parameters and click Calculate

Standard Dosing Reference

Scenario	Gestational Age	Recommended Dose
Sensitizing event (early)	< 12 weeks	50 mcg (mini-dose) or 300 mcg
Sensitizing event (mid/late)	≥ 12 weeks	300 mcg (1 vial)
Routine antenatal prophylaxis	28 weeks	300 mcg (1 vial)
Post-delivery (Rh+ baby)	At delivery	300 mcg (1 vial)
Large fetomaternal hemorrhage	Any	round(FMH mL / 30) + 1 vial, then × 300 mcg

Summary

RhoGAM (Rh immunoglobulin) is given to Rh-negative mothers to prevent sensitization after exposure to Rh-positive fetal blood. The standard dose is 300 mcg (one vial), covering up to 30 mL of fetal whole blood. This calculator helps clinicians determine the correct number of vials based on gestational age, the clinical indication, and the estimated volume of fetomaternal hemorrhage.

How it works

Enter the gestational age in weeks to determine the clinical scenario (early, mid, or late pregnancy).
Select the indication for RhoGAM administration (routine prophylaxis, sensitizing event, or large-volume hemorrhage).
Enter the estimated volume of fetal blood exposure if a fetomaternal hemorrhage (FMH) is suspected.
For a quantified fetomaternal hemorrhage, divide fetal blood volume by 30 mL, round to the nearest whole number, then add one safety vial.
The result shows the number of 300 mcg RhoGAM vials needed and the total dose in micrograms.

Use cases

Routine antenatal prophylaxis at 28 weeks gestation.
Post-delivery dosing when baby is confirmed Rh-positive.
After sensitizing events such as amniocentesis, chorionic villus sampling, or abdominal trauma.
Calculating dose after a large fetomaternal hemorrhage detected by Kleihauer-Betke test.
First-trimester miscarriage, ectopic pregnancy, or termination in Rh-negative patients.
Antepartum hemorrhage management in Rh-negative mothers.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu