Blood Type and Pregnancy: ABO, Rh-D, and HDFN

The antenatal antibody screen

The first antenatal blood tests in both the UK and US include ABO and Rh-D typing plus an antibody screen. The screen looks for red cell antibodies in the mother's plasma that could cross the placenta and affect the developing baby. The combination is sometimes called a type-and-screen. Booking timing is typically 8 to 12 weeks of pregnancy.

If the mother is Rh-D negative, a follow-up antibody screen is repeated at 28 weeks (UK NICE guidance) before the routine antenatal anti-D prophylaxis dose is given. Mothers with previously identified clinically significant antibodies (anti-K, anti-c, anti-E, anti-Fya, anti-Jka, and others) are referred to a fetal medicine centre for monitoring.

The NICE NG201 antenatal care guideline sets out the UK pathway. The American College of Obstetricians and Gynecologists publishes the US guidance. The protocols differ in some detail but the overall structure is similar.

ABO incompatibility

ABO incompatibility (most commonly a group O mother with a group A or B baby) can cause haemolytic disease of the fetus and newborn (HDFN), but the disease is typically much milder than the Rh-D version. Most affected newborns develop mild jaundice in the first few days of life and respond to standard phototherapy. Severe cases needing exchange transfusion are uncommon.

The clinical mildness has two reasons. First, anti-A and anti-B antibodies are predominantly IgM, which do not cross the placenta efficiently. Some IgG anti-A and anti-B is present in group O mothers and does cross, but the binding to fetal red cells is partly blocked by the wide distribution of A and B antigens in fetal tissues other than red cells.

ABO incompatibility is monitored postnatally rather than antenatally. The newborn is observed for jaundice, and bilirubin is measured if jaundice appears. Phototherapy is the standard intervention. The NICE CG98 guideline on neonatal jaundice covers the management algorithm.

Rh-D incompatibility: the more serious version

Rh-D incompatibility is the major reason blood type matters in pregnancy. If the mother is Rh-D negative and the baby is Rh-D positive (inherited from the father), fetal red cells crossing the placenta can sensitise the mother's immune system to produce anti-D antibodies. The first pregnancy is usually unaffected because sensitisation occurs at delivery. In subsequent pregnancies with a Rh-positive baby, the pre-formed anti-D crosses the placenta and can cause severe fetal anaemia, hydrops, and intrauterine death.

Anti-D immunoglobulin (RhoGAM in the US, anti-D in the UK) is given to Rh-negative mothers to prevent sensitisation. The current routine schedule includes a dose at around 28 weeks of pregnancy and a further dose within 72 hours of delivery if the baby is Rh-positive. Additional doses are given after sensitising events (miscarriage, ectopic pregnancy, antepartum bleeding, abdominal trauma, amniocentesis, external cephalic version).

See our dedicated anti-D immunoglobulin page for the dose, timing, and clinical evidence behind the prophylaxis programme. See our Rh factor pregnancy page for a deeper dive on the mechanism.

NIPT for fetal Rh-D status

Non-invasive prenatal testing (NIPT) using cell-free fetal DNA in maternal blood can determine fetal Rh-D status from about 11 to 13 weeks of pregnancy onwards. The UK NHS rolled out routine NIPT-RhD for Rh-negative women in 2021 following a 2017 cost-effectiveness analysis. About 35 to 40 percent of Rh-negative women are carrying a Rh-negative baby and can safely skip routine anti-D prophylaxis.

The US has not adopted routine NIPT-RhD on the same scale. Some private practices offer it; ACOG continues to recommend universal anti-D prophylaxis for Rh-negative women without fetal genotyping. The cost-benefit calculation differs between the universal-screening UK NHS context and the more fragmented US insurance-funded context.

The NICE DG25 guidance covers the UK NIPT-RhD pathway and the high-quality fetal Rh-D genotyping service offered by NHSBT.

Other red cell antibodies in pregnancy

Beyond ABO and Rh-D, several other red cell antibodies can cause significant haemolytic disease of the fetus and newborn. Anti-K (Kell antigen) is the second most common cause after anti-D. Anti-c (small c, the Rh antigen related to D), anti-E, anti-Fya (Duffy a), and anti-Jka (Kidd a) are also clinically important.

Mothers with these antibodies are referred to fetal medicine centres for monitoring. The middle cerebral artery (MCA) Doppler ultrasound, measured serially, is the modern non-invasive way to detect fetal anaemia. Intrauterine transfusion (IUT) is the established treatment for severe fetal anaemia, performed under ultrasound guidance.

The Royal College of Obstetricians and Gynaecologists (RCOG) Green-top guideline on the management of women with red cell antibodies during pregnancy covers the UK practice in detail.

Postnatal blood type testing of the baby

Cord blood is tested for ABO and Rh-D at delivery in many UK and US units, especially if the mother is Rh-D negative or has any other significant antibody history. The result determines whether the postnatal anti-D dose is needed (Rh-positive baby with Rh-negative mother triggers a 72-hour postnatal anti-D dose).

Newborns are also assessed for clinical signs of HDFN (jaundice, anaemia, hepatosplenomegaly). Severe HDFN may require exchange transfusion in the neonatal unit, performed with O-negative or type-specific blood depending on the situation. See our O-negative donation need page for the donor-supply context.

For routine cases, the baby's blood type may not be communicated to parents at the maternity unit; it can be requested from the GP or paediatric records later if there is a clinical reason. See our how to find your blood type page for the options.

Frequently asked questions

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