You are here: Home » Services » Maternity Services » Booking your maternity appointment » Antenatal blood tests and screening

Antenatal blood tests and screening

As part of your antenatal care, you will be offered a number of blood tests. Some are offered to all women and some are only offered if it is thought that you are at risk of a particular infection or inherited condition. All of the tests are done to help make your pregnancy safer or to check that your baby is healthy.

Blood tests

Talk to your midwife or doctor so that you understand why the blood tests are being offered and so that you can make an informed choice about whether or not you want them. Your midwife or doctor should also give you information about the tests. Below is list of the tests offered.

Anaemia
Your blood group, rhesus factor and antibodies
Immunity to rubella (German measles)
Syphilis
Hepatitis B
HIV

Blood group tests

Your blood group and rhesus factor are important in case you have to have a blood transfusion, and if you are Rhesus Negative you will be offered anti-D injections. Your midwife will discuss this with you in more detail. Rhesus disease can happen if a pregnant woman who is rhesus negative develops antibodies that attack the baby’s blood cells. This can then lead to jaundice or anaemia in your baby.

Screening for Hepatitis B, HIV and Syphilis

Screening for all of these are offered at the booking appointment, as it is important to detect any of these infections early for the wellbeing of you and your unborn baby. All can have implications as they can be passed from a mother to her baby through blood or body fluids. There is no risk associated with this test as it’s simply a blood test. It is your choice to have this blood test.

Immunity to Rubella (German Measles)

If you get rubella in early pregnancy, it can seriously harm your unborn baby. Your midwife or doctor will talk to you about what happens if your test results show low or no immunity. You will be offered measles, mumps and rubella (MMR) immunisation after your baby is born to protect future pregnancies.

Should you test positive to any of the above infections in pregnancy your care will be reviewed by the Antenatal Screening Co-ordinator who will discuss how this will affect your ongoing care.

Scans

Ultrasound Scans

You will be offered at least two ultrasound scans during your pregnancy. The first is usually around 10-12 weeks and is sometimes called the dating scan because it can help to determine when the baby is due. The second scan usually takes place around 20 weeks and is called the anomaly scan because it checks for structural abnormalities.

Anomaly Scan

All women will be referred for an anomaly scan around 20 weeks gestation. You will find information regarding the anomaly scan in your green notes (MHHR). This ultrasound scan provides you with an opportunity to see your baby and provides reassurance that all is well with your baby. However the main purpose of this scan is to screen for structural abnormalities of the baby such as Spina Bifida or heart defects. Detecting abnormalities such as a heart defect is important so that your baby can be delivered in the appropriate place and so that your baby’s care is managed appropriately when it is born. It also gives the parents time to prepare if their baby has a known condition.

For women with a normal uncomplicated pregnancy ultrasound scans are not recommended after 24 weeks (NICE, 2008).

Tests to detect abnormalities

There are other tests available that can screen for an increased risk of congenital abnormalities such as Down’s syndrome, Edward’s, Patau’s (chromosomal disorders) or spina bifida , which is a defect in the development of the spine Discussing the tests and what they mean with your partner, midwife and Doctor may help you in deciding what tests are right for you.

Screening tests can:

reassure you that your baby has no detected structural abnormalities
give you time to prepare for the arrival of a baby with special needs

Tests can also provide valuable information for your care during the pregnancy. However, no test can guarantee that your baby will be born without an abnormality. No test is 100% accurate and some abnormalities may remain undetected.

If you do have a screening test and it suggests an increased chance of a chromosomal abnormality, you will be offered diagnostic tests, which will give a more definite diagnosis. These diagnostic tests carry a small risk of miscarriage, so you may decide not to have them. Discussing the issues with your partner, midwife, doctor and friends may help you in deciding what is right for you.

Quadruple test or Quad test

Usually taken from 14 weeks. It is a blood test to measure various levels of substances in your blood. The cost of this test is around £27. The Quad screen is used to evaluate whether there is an increased chance of your baby being affected with certain conditions, such as Down’s Syndrome, Edward’s , Patau’s or neural tube defects. A low risk result can offer reassurance that there is a low chance of your baby having these conditions. The Quad test is however only a screening test and not a diagnostic test. A low risk result does not mean no risk and a high risk result does not mean your baby will have the condition. If it shows a high risk result you will be offered further diagnostic tests.

Harmony Test

This test is a more accurate screening test which costs around £290, but can detect baby cells in the mother’s circulation and these can be genetically tested for Down’s Syndrome (Trisomy 21), Patau’s and Edward’s syndrome (Trisomy 18). This test can be performed after 10 weeks gestation. Not all positive Harmony test results are true positives, so it is still recommended that you should have a positive result confirmed by Amniocentesis and you will be offered referral to fetal medicine for this.

Amniocentesis

Following a high risk or positive screening test for any of the above you will be referred to fetal medicine in the Royal Jubilee Maternity Hospital in Belfast. There a more detailed scan will be performed and they will offer you an amniocentesis usually after 15 weeks gestation. This procedure involves taking a small sample of the amniotic fluid surrounding your baby for analysis. Guided by an ultrasound a very fine needle is inserted through the abdomen and the sample is retrieved. This is then sent to genetics for chromosomal analysis. This test is a diagnostic test which should confirm if your baby has chromosomal abnormalities such as Down syndrome, Patau’s or Edward’s syndrome. Other less common abnormalities may not be detected.

One of the risks associated with an amniocentesis is miscarriage and it is estimated that 1 in every 100 women will miscarry following an amniocentesis.