Pregnancy blood tests – Blood group

Pregnancy (antenatal) blood tests are carried out during pregnancy to check on the health of you and your baby. One routine test identifies your blood group.

As part of your care during your pregnancy, you will be given a blood test to find out which blood type (group) you are. 

Blood group including Rhesus D (RhD)

There are 4 blood types (A, B, AB or O). You inherit your blood group from your parents so therefore it stays the same your whole life. These blood groups do not cause any issues in pregnancy, but can be useful to know after delivery, in case you need to be given blood, eg, if you have heavy bleeding (haemorrhage) during the birth or afterwards.

It is also recommended that another type of inherited blood group, called Rhesus D, is checked. You can be either Rhesus D positive (RhD +) or negative (RhD -).

If you are RhD + it does not cause any issues or require any treatment. However, if you are RhD -, it is possible to develop ‘antibodies’ as an immune response if some of your baby’s blood enters your bloodstream. This might occur if you have a ‘sensitising event’, eg, any bleeding in pregnancy, a miscarriage or abortion, a car accident or blow to the abdomen/puku, or during delivery. These antibodies remain for the rest of your life, and do not cause you any health problems. However, they can cause any babies you have in the future (and occasionally this baby) to become severely anaemic and jaundiced, which could even cause them to die. To reduce the chance of this happening, you will be recommended to have an injection of ‘Anti-D’ every time one of these sensitising events happens.

Blood group antibodies

There are over 50 different kinds of blood groups, and if another person’s blood ever enters your body (eg, from a blood transfusion or during a former pregnancy, as explained above) you may start making antibodies against a group that is different from yours. Some of these antibodies are harmless, but some in pregnancy can make the baby anaemic and even cause it to die. If antibodies are picked up, you will be referred to a specialist for discussion about monitoring your baby carefully, with very occasional treatment being required.

Learn more

Blood groups and types PatientInfo, UK
About blood NZ Blood Service

Reviewed by

Dr Janet Crofts is an obstetrician with further specialisation in maternal-fetal medicine. She is currently based in Auckland, and has trained in the UK, New Zealand and Australia.
Credits: Health Navigator Editorial Team. Reviewed By: Dr Janet Crofts. Obstetrician, Auckland Last reviewed: 17 Feb 2022