Understanding Screening Tests During Pregnancy: What You Need to Know

You've already mastered your first prenatal test: peeing on a stick!

And it looks like you've passed with flying colours. During pregnancy, you will be offered screening tests to check that you and your baby are healthy. Screening tests can provide you with information about your baby’s growth and development, and how your body is coping with the physical changes and demands of pregnancy. They can also tell you whether you or your baby are more likely to have a medical condition.

Screening tests and checks you may be offered include: the first antenatal blood test, urine screening, ultrasound scans, diabetes tests, antenatal screening for Down syndrome and other conditions, STI testing and family violence risk assessment. All of these screening tests are your choice. Your midwife or obstetrician will give you information and support to help you decide whether to have screening or not. Let's take a look together to learn more about these screening tests.

First antenatal blood test

During the first of your pregnancy visits with your lead maternity carer (LMC) you will be given a form to take to your local medical laboratory so you can have your blood tested. The first antenatal blood test is designed to check your health and the health of your baby by identifying conditions or diseases as soon as possible in your pregnancy so that treatment may be offered if required.

These blood tests check various things such as : your blood group and rhesus factor (positive or negative) 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 (German measles), if you are a hepatitis B carrier, several STI's and if you have diabetes or are at risk of developing diabetes during pregnancy. Mums who are rhesus-negative or have blood group antibodies will usually have further tests at 34 to 36 weeks. Mums with blood pressure problems, diabetes or other medical problems may need regular blood tests towards the end of their pregnancy.

Urine screening

Your urine will be checked multiple times during your antenatal visits using a simple dipstick test to detect if your urine contains: protein – this may indicate early pre-eclampsia (a rare complication of pregnancy), sugar (glucose) – this is an initial check for diabetes, bacteria – during pregnancy you can have a urinary tract infections without symptoms and because this may lead to kidney infections they may suggest you are treated with antibiotics.

Pregnancy ultrasound scans

Yay! You get to see fuzzy pictures of your little one. Ultrasound screening is offered for a variety of reasons, such as to determine when your baby is due, to see if you’re expecting twins (or more!) and to check if your baby is developing normally. There could be other reasons to have an ultrasound scan as your pregnancy progresses, such as monitoring the growth of your baby and the position of the placenta.

The four most common times to have a scan are:

• A Dating scan: You will be offered a scan in the first 14 weeks of your pregnancy to check when your baby is due and whether you are having multiples.

• Nuchal translucency scan: This is part of the first trimester combined screening for Down syndrome and other conditions. If you decide to go ahead with this optional screening test, you will be offered a scan between 11 weeks 2 days and 13 weeks 6 days (ideally 12 weeks). This is the only time that this scan can be performed.

• Anatomy scan: This is a detailed scan at 18 to 20 weeks to check the baby’s brain, heart, spine and other important organs. The great majority of babies will be normal and most parents-to-be find this anatomy scan very reassuring. Occasionally, an abnormality is detected and this can have important implications for your baby’s care. For example, it may be necessary to arrange for the baby to have a surgical procedure soon after birth. This is a very rare event and in most cases finding an abnormality can help paediatricians plan any treatment baby might need after it is born. It is also important to realise that not all abnormalities in a developing baby will be detected by an ultrasound scan. At this scan, you may be able to find out what sex your baby is (if the baby is cooperating) – although some parents are happy to have a surprise and wait until the baby is born.

• Growth scans: If the maternity care provider is concerned about the baby’s growth in the third trimester, then additional ultrasound scans at this stage may be recommended. Most women will not need any ultrasound scans after their 18 to 20 week anatomy scan.

Diabetes testing

You may have heard about this test from friends or family! This is done at 24 to 28 weeks of pregnancy to check if you are at an increased risk of developing gestational diabetes (diabetes in pregnancy). You will be given a sugary drink and an hour later some blood is taken at the lab. If your blood sugar is unexpectedly high you may need a further test called a Glucose Tolerance Test (GTT). For this test you will need to miss breakfast. Blood is taken to measure your “fasting” glucose levels before you are given a glucose drink and have more blood taken to measure glucose levels two hours later.

A positive polycose test is not a “panic situation” – about 10 to 15% of women will have a positive polycose test. Only about a third of women with a positive polycose test will go on to have gestational diabetes confirmed when they subsequently have a glucose tolerance test. Gestational diabetes is associated with high blood sugars in pregnancy. Exposure to high sugar levels can result in the baby becoming excessively large. Mums who develop gestational diabetes are also at greater risk of developing diabetes in later life.

Antenatal screening for Down syndrome and other conditions

There are two screening options available for Mums who are less than 20 weeks pregnant.

• First trimester combined screening: This is available if you are less than 14 weeks pregnant. It combines the results of your blood test and a nuchal translucency (an ultrasound measurement taken from the back of baby’s neck) with other information, such as your age and weight, to give a risk result.

• Second trimester maternal serum screening: This is available if you are 14–20 weeks pregnant (ideally between 14 and 18 weeks) and combines the results of your blood test with other information, such as your age and weight, to give a risk result.

If the screening shows that there is an increased risk for a genetic condition (like Down syndrome, Trisomy 13, Trisomy 18 or Turners syndrome), There is no need to have this later test if you have already had the earlier combined test.