Anti-D for threatened miscarriage before 12 weeks
The case
A 26-year-old woman, blood group O RhD-negative, presents to the emergency department at 10 weeks' gestation with 2 hours of painless light vaginal bleeding. She is haemodynamically stable. Transvaginal ultrasound confirms a viable intrauterine pregnancy with fetal cardiac activity. The cervical os is closed and the bleeding has slowed. This is her first pregnancy and she has no red cell antibodies. She asks whether she needs an anti-D injection. Which of the following most accurately reflects the appropriate anti-D management?
Options
- AGive 250 IU anti-D within 72 hours
- BNo anti-D for light, ongoing bleeding with a viable pregnancy before 12 weeks
- CAnti-D is not needed because the fetus is too small to sensitise her
- DGive 625 IU anti-D within 72 hours
- EPerform a Kleihauer test before deciding
Think it through before you read on. Which single option is best, and why are the other four wrong?
Show the answer and explanation
Answer
B. No anti-D for light, ongoing bleeding with a viable pregnancy before 12 weeks
Why this is the right answer
Anti-D immunoglobulin prevents an RhD-negative woman from making antibodies against RhD-positive fetal red cells that enter her circulation. Sensitisation in this pregnancy would put later RhD-positive babies at risk of haemolytic disease of the newborn.
The National Blood Authority guideline on the prophylactic use of RhD immunoglobulin in pregnancy care (2021, with RANZCOG endorsement) sets out which events need anti-D in the first trimester: miscarriage, termination, ectopic or molar pregnancy, and chorionic villus sampling. For these, the dose is 250 IU within 72 hours.
A threatened miscarriage before 12 weeks, where the pregnancy is viable and the bleeding is light, is treated differently. The guideline states that anti-D is not routinely recommended, because the volume of fetal blood transferred is very small and there is no evidence that prophylaxis changes outcomes in this situation. Anti-D should be considered if the bleeding is heavy, repeated, or associated with abdominal pain, and after any significant trauma.
The reason is not that sensitisation is impossible. Fetal red cells express RhD from about 6 to 7 weeks, and confirmed pregnancy loss before 12 weeks does get anti-D.
The 625 IU dose applies to sensitising events from 12 weeks onward, and the Kleihauer test, which measures the size of a fetomaternal haemorrhage, is used for events after 20 weeks to decide whether extra doses are needed. Routine prophylaxis at 28 and 34 weeks, and after delivery of an RhD-positive baby, will still be given later in this pregnancy.
Why the other options are wrong
- A
250 IU is the first-trimester dose for confirmed miscarriage, termination or ectopic, not for a threatened miscarriage with a viable pregnancy and light bleeding.
- C
The fetus can sensitise from 6 to 7 weeks; the reason for withholding is lack of evidence of benefit, not impossibility.
- D
625 IU is the dose from 12 weeks onward; it is not indicated at 10 weeks and routine anti-D is not recommended here.
- E
Kleihauer testing quantifies bleeds after 20 weeks; it is not relevant at 10 weeks.
High-yield takeaway
Before 12 weeks, give 250 IU anti-D for miscarriage, termination, ectopic or CVS, but not for a threatened miscarriage with light bleeding and a viable pregnancy.
Reference: National Blood Authority Guideline for the Prophylactic Use of RhD Immunoglobulin in Pregnancy Care (2021)
Common questions
What events need anti-D before 12 weeks?
Miscarriage, termination, ectopic pregnancy, molar pregnancy and chorionic villus sampling, at a dose of 250 IU within 72 hours.
When would anti-D be given for a threatened miscarriage?
If the bleeding is heavy or repeated, associated with abdominal pain, or follows significant trauma.
Related free cases
No account. No card.
Try twenty of these, unmarked.
A worked case shows the reasoning. A session shows you where you stand.
No account. No card.