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Rh Incompatibility in Pregnancy: When You May Need Anti-D Immunoglobulin

NNova editorial team · 6 min read

Anti-D immunoglobulin may be recommended for an Rh-negative pregnant person when there is a chance of mixing with Rh-positive fetal blood. It is commonly given around 28 weeks, after birth if the baby is Rh-positive, and after bleeding, procedures, trauma, or pregnancy loss.

What Rh incompatibility is

Rh incompatibility is not a disease. It is a difference in blood type. The mother is Rh-negative, and the baby may be Rh-positive. A problem can develop if fetal blood cells enter the mother’s bloodstream and her immune system starts making antibodies against them.

This does not happen in every Rh-negative pregnancy. The risk depends on whether fetal blood has mixed with the mother’s blood and whether she has already received anti-D.
  • around 28 weeks as routine prevention
  • after birth, if the baby is Rh-positive
  • after bleeding during pregnancy
  • after amniocentesis, chorionic villus sampling, or abdominal trauma
  • after miscarriage, abortion, or ectopic pregnancy

Why timing matters

ACOG generally recommends giving anti-D within 72 hours of an event that could let fetal blood reach the mother. Giving it later may still help in some cases, so ask your doctor or midwife about timing if you are unsure.

When to contact your care team right away

  • any vaginal bleeding
  • abdominal trauma or a fall
  • a noticeable drop in your baby’s movements
  • you do not know your Rh status or antibody test result
If antibodies are already present, your care team may monitor antibody levels, ultrasound findings, and your baby’s well-being more closely. Your care plan will depend on your results.

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General information only; it does not replace advice from your doctor or midwife.