Antenatal blood tests are designed to protect your health and the health of your baby and family/whānau by identifying conditions or diseases as soon as possible in your pregnancy so that treatment can be offered.
When you first see your family doctor, midwife or specialist doctor during pregnancy you will be offered a blood test. This blood test is free and is taken from one blood sample. It checks:
- your blood group and rhesus factor
- if there are any antibodies that may be harmful to your baby
- your haemoglobin (the amount of iron in your blood)
- if you are immune to rubella
- if you are a hepatitis B carrier
- if you have syphilis
- if you have HIV
- if you have diabetes or are at risk of developing diabetes.
An optional antenatal blood test is to screen for Down syndrome and other conditions (see more below).
ABO blood group test
Your blood group can be A, B, O or AB.
- Your blood is checked for your group and for the presence of antibodies (part of your immune system).
- Certain antibodies can be harmful to your baby during pregnancy.
- If you are found to have antibodies that could affect your baby, monitoring and treatment to protect your baby are recommended.
Rhesus blood group test
This is another blood group test to check for rhesus factor (mainly Rh D). Your blood group either has or does not have this factor present, so you are either Rh positive (Rh+) or Rh negative (Rh–).
- If you are Rh– and your blood mixes with your baby’s blood, you can make antibodies that can cause severe anaemia and jaundice in this or your next baby.
- Your blood can mix with the baby’s if you have an antenatal bleed, miscarriage or abortion, or it can happen during the birth.
- An injection of ‘anti-D’ after any of these events can prevent your body from making these potentially harmful antibodies.
Iron and full blood count
The full blood count is a test that checks whether your body has enough iron to manage the extra requirements of pregnancy.
- If your iron levels are low, you will feel more tired and will be less able to manage the loss of blood that occurs during birth.
- You will be offered advice about how to increase the iron in your diet and/or iron tablets.
The full blood count also checks your platelet levels. Platelets help your blood to clot.
Rubella (German measles)
This test checks that you are immune to (protected against) rubella, also known as German measles. If you catch the rubella virus in pregnancy it can lead to severe problems for your baby (eg, deafness or brain injury) or miscarriage.
If you are not immune, you can have a vaccination to prevent problems in future pregnancies.
- This vaccination can only be given when you are not pregnant.
- It is best carried out soon after you have given birth or following a miscarriage or termination of pregnancy.
Hepatitis B is a virus that can be passed to a baby during birth. You may have this disease but not know because there are often no symptoms. It can also be passed on to your family/whānau through contact with infected blood.
- Hepatitis B can cause significant health problems, including liver damage.
- About 20% of babies exposed to hepatitis B during birth, and left untreated, become infected.
- Over 90% of untreated babies become carriers of the virus.
If your lead maternity carer (LMC) knows you have hepatitis B, they can offer your baby immunoglobulin and vaccination at birth to help prevent your baby becoming infected. Your LMC can provide further information about hepatitis B.
Syphilis used to be a rare infection in New Zealand, but it is becoming more common. Most women with syphilis do not know they have the disease because they feel well and have no symptoms.
- Syphilis can be passed on either sexually or from mother to baby during pregnancy.
- If left untreated, it can cause serious health problems for you and your unborn baby.
- A blood test in early pregnancy, and then early treatment if needed, can help to avoid these problems.
Human immunodeficiency virus (HIV) affects your body’s ability to fight infection and can cause AIDS.
- HIV is passed on to others by contact with blood or body fluids.
- If you have HIV, it can be passed on to your baby during pregnancy, birth or breastfeeding.
- HIV tests are now offered to pregnant women because the risk of your baby becoming infected can be reduced from between 25%–31.5% to less than 1% if you are diagnosed and treated during pregnancy, do not breastfeed your baby and your baby is treated with medicine in the first six weeks of life.
- New medicines not only protect your baby but can also make a big difference to your health, helping you to stay well for yourself and your family/whānau.
In 1 in 1000 tests, the woman will need to have a second blood test to confirm her HIV test is negative. This is because this test is so sensitive it occasionally picks up some antibodies that are not HIV. In most of these cases, the second blood test will show the woman does not have HIV.
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Diabetes is when you have too much sugar in your blood, and it can make you sick and affect your baby’s growth. Diabetes screening is to check whether you already have diabetes or if you are at risk of developing diabetes while you are pregnant (gestational diabetes).
Diabetes screening is offered twice:
- as part of the first antenatal blood test (or any time up until you are 20 weeks pregnant)
- again when you are 24–28 weeks pregnant.
There are three blood tests that can help you find out if you have or are at risk of getting diabetes during your pregnancy. The three tests are:
- oral glucose challenge test (OGCT)
- oral glucose tolerance test (OGTT).
For more information on these tests see Testing for Diabetes in Pregnancy (pdf, 233 KB)
If you do already have diabetes or you develop diabetes in pregnancy, you will be offered information, treatment and support, including help to eat well and stay active.
Down syndrome and other conditions screening
Antenatal screening for Down syndrome and other conditions are available for pregnant women in many countries, including New Zealand. These screening tests (combined blood test and nuchal translucency scan in the first trimester, or blood test in the second trimester) can show the likelihood of a foetus having Down syndrome or some other conditions.
The screening tests:
- do not give a final result, but women whose screening results showed increased risk, will then be offered diagnostic tests, e.g. chorionic villus sampling or amniocentesis.
- should prevent some women from having to undergo the more invasive diagnostic tests, if their screening results show a low risk of Down syndrome and other conditions.
More about the screening tests is available from the National Screening Unit Ministry of Health, NZ.
Your results will be available from the health professional who organised your blood tests.
All test results are confidential. If you need any support, information or treatment you will be referred to the appropriate healthcare professional and receive care that is professional, respectful and confidential.
If you have any questions after reading this article please ask your midwife, GP or specialist. The Ministry of Health NZ recommends that you have these tests as soon as possible after you know you are pregnant because knowing whether you have these conditions can help keep you and your baby well.
Before having any blood tests you must have the opportunity to receive information about the tests and then make an informed decision as to whether or not you wish to have them. The decision to have these blood tests is yours. Your decision will be respected.
Code of Health and Disability Services Consumers’ Rights
The Code of Health and Disability Services Consumers’ Rights spells out your rights when using any health services. You have a number of rights under the code, including:
- your right to the information you need to make decisions about your health – this information should be given to you in a way that you can understand
- your right to make an informed choice and give informed consent before you receive treatment
- your right to be treated with respect, taking into account your cultural needs and values
- your right to services being provided with reasonable care and skill.
If you want more information about your rights, you can contact the Office of the Health and Disability Commissioner, freephone 0800 11 22 33 or see their website.
If you would like more information about these or other screening tests/programmes, or need to have information in a different language, please ask your midwife, GP or specialist or visit the National Screening Unit.