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Blood tests during pregnancy

4-minute read

As part of your antenatal care you’ll be offered several blood tests. Some are offered to all women, and some are only offered if you might be at risk of a particular infection or inherited condition.

All the tests are done to check for anything that may cause a problem during your pregnancy or after the birth, or to check that your baby is healthy, but you don’t have to have them if you don’t want to.

Talk to your doctor or midwife and give yourself enough time to make your decision. They should also give you written information about the tests. Below is an outline of all the tests that can be offered.

Blood group

There are 4 blood types (A, B, AB or O) and you will be given a blood test to find out which type you are. It is useful to know your blood group in case you need to be given blood, for example if you have heavy bleeding (haemorrhage) during pregnancy or birth.

Rhesus (RhD) factor

When you find out your blood group, you will also find out if your type is positive or negative. This is your 'Rhesus (RhD) factor', which indicates if you have a substance known as 'D antigen' on the surface of your red blood cells. If you do, you are RhD positive, if you don't, you are RhD negative. Most people in Australia are positive, around 17% are negative.

If your blood is RhD negative, it isn’t usually a problem, unless your baby happens to be RhD positive. If it is, there’s a risk that your body will produce antibodies against your baby’s blood. This usually won’t cause a problem for your first pregnancy, but could impact future pregnancies. If you are Rhesus negative, you will need an injection at 26 to 28 weeks and at 34 to 36 weeks to protect the baby.

Find out more about being Rhesus D negative in pregnancy.

Anaemia

It is very common for women to develop anaemia, or iron deficiency during pregnancy. This is because your body needs extra iron so your baby has a sufficient blood supply and receives necessary oxygen and nutrients. Increasing the amount of iron-rich food you consume during your pregnancy can help avoid iron deficiency anaemia. Some pregnant women require an iron supplement, particularly from the 20th week of pregnancy. Anaemia makes you tired and less able to cope with any blood loss during labour and birth.

Your midwife or doctor can tell you if you need iron tablets to prevent or treat anaemia. Your iron levels will be checked throughout your pregnancy.

Infections

Your blood test will also look for a number of infections that may affect your pregnancy or your unborn baby.

It's important to remember that you can still catch all these infections during pregnancy after you’ve had a negative test result. This includes sexually transmitted infections such as syphilis, HIV and hepatitis B if you or your sexual partner take risks, such as having unprotected sex. You can also get HIV and hepatitis if you inject drugs and share needles. Your midwife or doctor can discuss this with you.

Gestational diabetes

Gestational diabetes (GDM) is a type of diabetes that affects some women during pregnancy. Diabetes is a condition where there is too much glucose (sugar) in the blood.

In most cases, gestational diabetes develops in the third trimester (after 28 weeks) and usually disappears after the baby is born. However, women who develop gestational diabetes are more likely to develop type 2 diabetes later in life.

Find out more about gestational diabetes.

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Last reviewed: May 2020


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