Prenatal Methods of Testing

Prenatal tests are important in monitoring the health of you and your unborn baby. There are a number of prenatal tests that women may have during their pregnancy. These prenatal tests can aid in identifying any potential problems and also reassure you if you are worried about the health of your baby. The very first prenatal test occurs when you suspect you are pregnant, and you may be given a blood test or urine test to confirm the pregnancy. If you find that you are pregnant you will then be given various different prenatal tests throughout the course of your pregnancy.

Types of Prenatal Tests

Blood Tests

Blood Tests are carried out routinely during pregnancy. Once you have your pregnancy confirmed you will have a blood test to check the following factors:

  • Your Blood Group
  • Whether you are rhesus positive or negative
  • Red blood cell abnormalities such as sickle cell and thallassaemia
  • Immunity to rubella (German measles)
  • Your iron levels to test your haemoglobin level
  • HIV/ AIDs testing
  • Hepatitis B
  • Syphilis

The doctor or midwife handling your prenatal care will discuss the blood tests with you and give you the opportunity to accept or decline the tests if you so wish. It is important to know your blood group in case you need a blood transfusion during pregnancy or birth.

Rhesus Positive or Negative

It is crucial to know if you are rhesus negative or positive because it determines the presence of either positive or negative red blood cells. If the doctor does not know whether you are rhesus negative or positive, the antibodies could destroy your baby’s red blood cells.

Just over 80% of people have the ‘rhesus factor’ in their blood and are therefore rhesus positive. However, problems can arise if the mother is rhesus negative and conceives a baby with a rhesus positive partner. As the foetus’s rhesus positive red blood cells pass into the woman’s bloodstream, her rhesus negative immune system naturally attacks them. In turn this can destroy the baby’s red blood cells, leading to anaemia and even jaundice, which can cause a short lifespan in very rare cases. Most mildly affected babies require no special treatment after delivery, but testing is essential.

By testing for rhesus during prenatal care, doctors take crucial steps to give any damaged baby the best chances for recovery. Rhesus negative mothers are tested frequently throughout pregnancy to check on mother and baby. Amniocentesis, or even a blood sample from the umbilical cord, can tell doctors whether significant damage has been done to foetal blood cells. Early delivery is commonplace for severely affected babies, after which any necessary treatment can be administered.

Sickle Cell and Thallassaemia

If you have the test for sickle cell and thallassaemia you can determine if you have a blood disorder, which could consequently make you anaemic. There are different tests available for the various ethnic minorities and your midwife or doctor will be able to offer further advice about which test is suitable.

Mothers-to-be with sickle cell anaemia are potentially at risk from further problems, but these should be anticipated at the first prenatal visit when the condition is found. In addition to giving you folic acid supplements and suitable care, more tests are ordered in order to be safe. These include a full blood count, liver function testing, and haemoglobin electrophoresis.

Rubella (German measles)

If you are not immune to rubella then you may be asked to have a vaccination to protect you against the illness. It is worth protecting you and your baby. If you catch rubella while you are pregnant it could cause harm to your baby’s hearing, sight and heart. It is therefore best to be protected.

The rubella immunity test is available before or during pregnancy. It lets you know if you are immune to the condition, and taking the test is always preferable because vaccines (usually taken in school years) can wear off relatively quickly. As vaccinations place a live virus within the body, the rubella jab is unsafe during pregnancy. This is why you should think about taking the immunity test before you become pregnant.

Iron Levels

Your Iron levels will be monitored to test your haemoglobin content. This can determine whether you are anaemic. Many pregnant women become anaemic during pregnancy and may be prescribed iron tablets by their doctor or midwife. In some cases of iron deficiency, you may be advised to take calcium supplements prescribed by your doctor, and also, recommended a well balanced iron enriched diet.

HIV & Aids Testing

If you have contracted the sexually transmitted disease AIDs then certain preventative measures can be taken to reduce the risk of the disease passing onto your baby during pregnancy.

This is extremely important as the HIV infection is easily passed on to babies at multiple possible points: during pregnancy, labour, delivery, and subsequent breastfeeding. If doctors can identify the virus and intervene early in pregnancy, the risk of passing on HIV is decreased dramatically. HIV tests should be offered as a routine part of your prenatal care, particularly if your risk of having the virus is considered high. A blood test is used to screen for the virus, and this takes place between 10 and 12 weeks into pregnancy.

Hepatitis B

If you find that you have Hepatitis B then there may be a risk of damage to your baby’s liver. Preventative measures can be arranged to protect your baby during pregnancy and after birth. Normally, an injection is given prior to birth.

In some cases the virus can be spread to the developing foetus; this largely depends on when the mother contracted the illness. The chances of infecting the baby are low when the mother gets the virus within the first trimester, but having hepatitis later in pregnancy can increase the likelihood to almost 90%. An infected newborn has a high risk of becoming a carrier, meaning that they could also pass the infection to others.

All women should be tested for Hepatitis B at their first prenatal visit. This involves taking a blood test which is examined for traces of the protein antigen found in those with the illness. If the mother is infected, proper measures will be taken to ensure the safety of others and vaccination. Other tests are used to assess the infected woman’s liver.


If syphilis is not identified and treated then it can cause abnormalities in your baby so it is best to get it treated as early as possible.

Syphilis is regularly transmitted to the baby in the process of natural birth and sometimes through caesarean section, in addition to the risks of transmission during pregnancy. Congenital syphilis is widespread and can lead to miscarriage and stillborn babies. Early diagnosis will greatly reduce the risk of complications as medical professionals can isolate this easily curable disease and treat it in the mother. Over 98% of babies do not contract congenital syphilis if the mother is treated by week 16.

Ultrasound Tests

Ultrasound tests can be used to help screen for genetic defects and to assess the general health of your baby. Ultrasounds are normally arranged 12 weeks into the pregnancy, and again at 20 weeks. Further ultrasound scans may be given if problems have been identified. Ultrasound tests are normally performed at the hospital where you have your prenatal care. For more information Ultrasound tests click here.


Amniocentesis tests are carried out to determine if your baby has a chromosomal disorder or fetal lung maturity. Amniocentesis is a test performed with a needle, which is placed through the abdomen into the uterus to obtain a sample of amniotic fluid. The test can be carried out 11 weeks into pregnancy up to 34 weeks. For more information on Amniocentesis click here.

Chorionic Villus Sampling (CVS)

Chorionic villus sampling is carried out to identify any serious problems with the feotus. A sample of the cells in the placenta is taken and is then tested for genetic defects. Chorionic villus sampling is recommended for pregnant women who are at risk of having a baby with Down’s syndrome. For more information on Chorionic villus sampling click here

Nuchal Fold Translucency Test

The nuchal fold translucency test is the latest state-of-the-art screening test for Down’s syndrome. The nuchal test is performed via ultrasound to measure the amount of fluid between the two layers of skin behind the baby’s neck.

Baby’s who have Down’s syndrome will have a greater collection of fluid than those who don’t. The measurement of fluid is read by a computer, along with your age, to assess the risk of Down’s syndrome.

The results from the test will give you an indication of whether your baby may have Down’s syndrome or not. The results come in the form of a risk factor, for example a 1 in 100 chance. Only 7 per cent of women are currently offered the nuchal fold ultrasound scan under the NHS; however, women who do want the test can choose to have it privately. The cost of a nuchal ultrasound test performed privately ranges from £90-150 in the UK.

There are also more advanced 3D ultrasound tests which can be done at an increased price if you want to further investigate whether your baby has Down’s syndrome or not.

Alpha-fetoprotein (AFP) Testing

The AFP test is designed to test for neural tube defects (NTD), such as Spina Bifida amongst many others. The AFP consists of many tests, such as the Triple or Quad screening tests, as discussed below.

Triple Screening Test

The triple screening test is a blood test that measures the alpha protein, HCG and Unconjugated Estriol. The result of the triple screening blood test can establish if there are any risks of birth defects such as Down’s syndrome. The test results can only show if there may be a problem, but cannot however guarantee that your baby definitely has a birth defect. Sometimes the blood results will come back as abnormal due the baby being younger or older than they really are. This often happens when the gestational age has been incorrectly estimated.

The triple screening test cannot test for all birth defects and there may be some that show up at a later stage of pregnancy. Ideally, the triple screening test should be carried out from 16-18 weeks during pregnancy; however, they may also be done up to 22 weeks into pregnancy.

If the test results do come back abnormal then your doctor will do further tests and may even carry out an ultrasound scan. You may also be offered an amniocentesis test in cases of suspected Down’s syndrome.

Quad Screening Test

The quad screening test is designed to measure the levels of HCG, alpha protein, Estriol and Inhibin A. The quad screening test is similar to the triple screening test; however, the quad screening test looks for an extra substance called Inhibin A which is a protein produced by the placenta and ovaries.

The quad screening test can also aid in identifying birth defects such as Down’s syndrome and gives a more detailed evaluation of the risks of such defects. The quad test is performed by taking blood from the mother, after which the blood sample is taken to the hospital to be tested. The results from the quad test normally take a few days to process. However, doctors are understanding of the anxiety of parents wanting to know the results and try to issue them with a response as punctually as possible.

There is no evidence of any side effects from having the quad screening test as it is simply a blood test. The quad screening test is normally offered when the mother reaches 16-18 weeks. All pregnant women are offered the quad screening test and it is particularly beneficial to have the test done if the mother has already had any babies with birth defects or any family history of birth defects.

The quad screen test can identify high levels of alpha protein, which may suggest a form of neural tube disorder such as Spina Bifida which is the abnormality in the spine of the baby. The quad screen test results may require additional tests, typically performed in the form of an ultrasound scan.

Glucose Tolerance Test during Pregnancy

The test is done to establish whether the mother has gestational diabetes or glucose intolerance during pregnancy. Many women temporarily suffer from diabetes during pregnancy, even if they have never been diagnosed with the condition before. However, diabetes during pregnancy may subside once the baby is born.

The glucose tolerance test can aid in identifying whether the mother is diabetic, with the test normally being carried out by way of a blood test. You may be asked to fast or have a glucose sugar drink, and then your sugar levels will then be tested.

The glucose tolerance test is normally offered to women in the 28th week of pregnancy; however, if you have a family history of diabetes then the test may be offered at an early gestational date.

The results are benchmarked and if the reading given by your doctor complies with the average normal level of glucose than you may not be diabetic. If the reading is higher than normal, you may have gestational diabetes. Your doctor or midwife will be able to further advise you on what is best for your diet and wellbeing.

Non Stress Test

The non stress test is designed for mothers who are overdue to test the wellbeing of the baby. In some cases this test is done to ensure precautions are in place in case the baby has to be delivered by C-section. The test is normally performed by your doctor or midwife, and a Doppler machine may be used to check the fetal heartbeat of the baby.

The test is performed between the 38th and 42nd week of pregnancy. The test monitors the response of the baby. A reactive or non reactive result will be given before taking further steps.

The procedure is painless and involves monitoring of the baby’s heartbeat during movement and at rest. It can take between 30 minutes and an hour, during which time the mother lies on their left side and leans back with support from a wedge. The technician attaches a device for hearing the baby’s heartbeat to the mother’s abdomen, and another that records contractions within the uterus. Sometimes the mother is required to press a button whenever they feel the baby moving. After analysing the results, the technician may recommend to induce labour or wait a little longer for a natural birth, repeating the test every week.

Bio Physical Profile Test

The bio physical profile Test is performed when the mother goes beyond her due date, at around 38-42 weeks pregnant. The bio physical test involves a detailed ultrasound of your baby, and the movement of the baby will be closely monitored. The ultrasound will look closely at the baby’s arms and legs and analyse the muscle tone and flexibility of the baby. Your baby will then be given a score from 0-2, 0 being abnormal and 2 being normal.

This test is most commonly ordered when a nonreactive result is obtained from the non stress test (discussed above). It can also be a necessary safeguard if the mother has had problems in an earlier pregnancy, or is at risk of complications due to diabetes, high blood pressure, poor intrauterine growth of the foetus, or a previous loss of a baby in the second or third trimester. Worrying overall scores may lead to induction or a caesarean section.

Stress Test

The stress test is performed to see how your baby reacts to the stress of contractions through labour. The test is performed by giving the mother an injection of pitocin and this is normally given just before inducing a labour. The results are measured as a pass or fail; if the baby passes it will be left alone to come out naturally, but if it fails then the mother may need to be induced or have a caesarean section.

For more information on birth defects click here

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