ABO and Rhesus incompatibility in pregnancy

Pregnancy blood tests identify the mother's blood group and look for antibodies. A clinician interprets the exact antibody, its level or pattern, and whether the baby could carry the corresponding blood-group marker.

Rh(D) incompatibility can arise when a pregnant person is RhD negative and the baby is RhD positive. Exposure to RhD-positive blood may prompt sensitisation, meaning the immune system makes anti-D antibodies. Those antibodies can cross the placenta and break down fetal red blood cells in a current or later pregnancy.

ABO incompatibility occurs when maternal antibodies react with the baby's A or B blood-group markers. Its effects are often identified in the newborn through jaundice or anaemia. Anti-D does not prevent ABO incompatibility; it is specifically used to reduce RhD sensitisation.

Attend scheduled antenatal blood tests and tell your maternity team about previous pregnancies, miscarriages, abortions, transfusions, or known red-cell antibodies. If you are RhD negative and not already sensitised, anti-D may be offered during pregnancy and after events where fetal blood might enter your circulation, including birth when the baby is RhD positive.

When a clinically significant antibody is present, the maternity team may arrange repeat blood tests and fetal monitoring. After birth, the baby's blood group, haemoglobin, and bilirubin may be checked, with treatment guided by the results and clinical examination.

Contact your maternity service promptly after vaginal bleeding, abdominal injury, or an invasive pregnancy procedure if you are RhD negative or do not know your blood group, because the timing of assessment and preventive treatment matters. Seek urgent pregnancy care for heavy bleeding, severe abdominal pain, fainting, or reduced fetal movement.

After birth, obtain urgent medical assessment if the baby becomes increasingly yellow, is difficult to wake, feeds poorly, seems unusually floppy, breathes rapidly, or looks pale. These signs require examination and cannot be judged safely from blood-group information alone.

Ask for your ABO and RhD results, whether the antibody screen found anything, whether anti-D is appropriate for you, and which events should prompt an extra dose. If an antibody has been detected, ask what it is, whether it can affect this baby, what monitoring is planned, and what checks the newborn will need.