Rh isoimmunization in pregnancy — Frequently asked questions (FAQ)
1) What does this algorithm cover?
The algorithm guides the prevention and management of Rh isoimmunization in pregnancy, including identification of the RhD-negative pregnant woman, systematic irregular antibody screening / indirect Coombs test, monitoring of potentially sensitising events and indication for prophylaxis with anti-D immunoglobulin. It also includes criteria for hospital referral in cases of alloimmunization.
2) What is irregular antibody screening and why is it important?
Irregular antibody screening, also known as the indirect Coombs test, detects maternal antibodies against fetal red blood cell antigens. It allows early identification of alloimmunization, guiding decisions about prophylaxis and the need for specialist follow-up when positive.
3) When should irregular antibody screening be performed?
It should be performed at the first antenatal visit and repeated between 24–28 weeks, always before routine anti-D administration. It should also be considered after sensitising events, such as bleeding or invasive procedures.
4) What are potentially sensitising events?
These are situations that may cause fetomaternal haemorrhage, allowing fetal red blood cells to enter the maternal circulation. They include bleeding during pregnancy, pregnancy loss, abdominal trauma, external cephalic version, invasive procedures such as amniocentesis, and delivery itself.
5) When should anti-D immunoglobulin be administered?
It is indicated in non-sensitised RhD-negative pregnant women after potentially sensitising events and as routine antenatal prophylaxis between 28–30 weeks. Postpartum, it should be administered if the newborn is RhD positive, ideally within 72 hours.
6) What is the aim of antenatal prophylaxis?
Antenatal prophylaxis aims to prevent maternal sensitisation resulting from subclinical fetomaternal haemorrhage, which is common in late pregnancy. Its use has significantly reduced the incidence of fetal and neonatal haemolytic disease.
7) What should be done if the antibody screen is positive?
A positive antibody screen suggests alloimmunization and requires referral to obstetrics/fetal medicine. In these cases, anti-D prophylaxis is not indicated, and specialist follow-up with assessment of fetal risk is required.
8) Is it necessary to repeat antibody screening after anti-D administration?
No. After anti-D administration, the antibody screen may become positive due to passive antibodies, which does not correspond to true alloimmunization. Therefore, repeat testing is not necessary unless clinically indicated.
9) What is fetomaternal haemorrhage and when should it be quantified?
Fetomaternal haemorrhage refers to the passage of fetal blood into the maternal circulation. It should be considered in high-risk situations, such as significant bleeding, trauma or delivery complications, and may be quantified using tests such as Kleihauer-Betke or flow cytometry to adjust the anti-D dose.
10) Is there an alternative to universal antenatal prophylaxis?
In some settings, fetal RhD genotyping using cell-free fetal DNA in maternal blood may be used. If the fetus is RhD negative, unnecessary antenatal prophylaxis can be avoided, although this approach is not universally available.
11) What happens if prophylaxis is not administered?
Failure to administer prophylaxis may lead to maternal sensitisation and development of anti-D antibodies, increasing the risk of haemolytic disease in future pregnancies, including fetal anaemia, hydrops fetalis and the need for intrauterine transfusions.
