An unsensitized Rh-negative woman undergoes suction evacuation for a missed miscarriage at 8 weeks gestation. She received no antenatal anti-D earlier. What is the correct dose of anti-D immunoglobulin she should receive within 72 hours?

• A 300 microgram (1500 IU) intramuscularly
• B 100 microgram (500 IU) intramuscularly
• C 50 microgram (250 IU) intramuscularly ✓
• D No anti-D required before 12 weeks

Explanation

Before 12 weeks gestation the fetal blood volume is small, so a sensitizing event such as miscarriage, ectopic pregnancy, or termination requires only the mini-dose of 50 microgram (250 IU) anti-D. The full 300 microgram dose is reserved for events after 12 weeks, delivery, and large fetomaternal hemorrhage, making option A excessive here. Option D is wrong because even early first trimester procedures carry a small sensitization risk, particularly after surgical evacuation. If gestation is uncertain beyond 12 weeks, give the full dose.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.