Routine Pregnancy Screening
Screening tests are recommended for all pregnant women. We use them to assess the health of you and your baby. When performed at the prescribed time, these tests act as an early warning system if there are issues.
There are two types of test:
- Screening tests – are offered to all pregnant women to assess the chance of you or your baby having a health problem.
- Diagnostic tests – are performed to find out whether your baby has a specific condition.
While screening offers an excellent way to assess how likely it is that your baby has a health problem, it may not detect any or all issues. Your midwife or health care provider will explain these tests. If you do not want to undergo any, please talk this through with your midwife or doctor. If you make an informed decision about declining these tests, your choice will be respected.
Screening tests1
8–12 weeks
Routine blood tests:
- Haemoglobin – tests the oxygen-carrying capacity of your blood
- Blood group – determines your blood group in case of need for treatment or transfusion. To read more about blood groups please click here to read a dedicated post.
- Antibodies – determine if you have built resistance to other blood types, usually through exposure
- Syphilis, Hepatitis B, Hepatitis C, HIV, Chicken Pox and Rubella immunity as early as possible.
These may be repeated later during pregnancy.
8–11 weeks
- Ultrasound dating scan – measures the length of your baby from head to tail (crown-rump length). As all babies grow at the same rate until about 12 weeks, your baby’s length is a reliable measure of gestation. After this time, the baby’s size can be affected by many factors and dating the pregnancy by ultrasound is less accurate.
11–14 weeks
- Combined First Trimester Screen (CFTS) paired with a nuchal translucency ultrasound. This test screens for trisomy (including Down syndrome) and may help identify some problems with baby’s development.
- Non-Invasive Prenatal Test (NIPT or Harmony). This test screens for genetic anomalies by taking YOUR blood and extracting your baby’s DNA from your sample. The NIPT test can also determine the sex of your baby at a very early stage.
18–21 weeks
- Foetal anomaly (morphology) scan. Looks at whether your baby has formed all necessary body parts and identifies the location of the placenta. The length of your cervix may also be measured at this ultrasound. This scan is the most reliable for finding out what sex your baby is.
- Early Glucose Tolerance test (if indicated).
28 weeks
- Glucose Tolerance Test
- Full blood count +/- iron studies – shows how you are using and storing iron
- Rhesus antibodies (for women with a negative blood group).
34 – 36 weeks
- Full blood count +/- iron studies – shows how you are using and storing iron
- Rhesus antibodies (for women with a negative blood group)
Ultrasound scans
An ultrasound scanner uses high-frequency sound waves that bounce off solid objects (like tissue and bone). These feedback to the scanner and it creates an on-screen picture. While it is nice to see an image of your baby, the primary goal of an ultrasound is to look at your baby’s body and collect information about growth and development. 4-D scanning offers the most accurate technology to provide a picture of your baby before they are born.
An ultrasound can demonstrate:
- Your baby’s size (important for estimating your due date and ensuring baby is growing as expected)
- Whether your baby is head up, head down or somewhere in between (significant at the end of your pregnancy)
- Whether twins (or more!) are present
- That your baby’s organs and bones are developing properly
- May show some abnormalities or problems (but it is not always possible to identify them). If your ultrasound reveals an unexpected issue, we will refer you for further diagnostic tests.
- Where your placenta is lying (a low-lying placenta may cause bleeding in late pregnancy or may block the birth canal requiring birth by caesarean section).
What happens?
Early scans will need you to fill your bladder before you start by drinking lots of water. As your bladder fills, it pushes the uterus up and allows your sonographer to get a better picture. It’s a bit uncomfortable for you, as you may want to go to the toilet.
We will ask you to lie down on a cushioned table, and the sonographer stands or sits next to you. You’ll need to lift your clothes and uncover your tummy. Gel is then spread on your abdomen and a hand-held instrument (called a transducer) rolled over your belly. This transducer puts out and picks up the sound waves, producing a picture of everything underneath it and transmits it to a screen.
Sometimes it is necessary to perform the scan vaginally. This scan involves an elongated transducer, which is covered and inserted into your vagina. While uncomfortable (in many ways) it enables a more unobstructed view of your cervix and uterus. This view may be important in some cases.
The few cases where ultrasound reveals an unexpected problem are referred for discussions regarding diagnostic tests such as amniocentesis or chorionic villus sampling (CVS). If this is the case please discuss these tests, their risks and benefits with your specialist.
We can also use ultrasound to determine the exact position of the baby to allow the doctor to carry out these tests. Pregnancy screening identifies mothers and babies who may have rare but serious conditions. Most mothers and babies screened will not have any of the conditions, but, for the small number that does, the benefits of screening are enormous. Early treatment can improve their health and prevent severe disability or even death.
Dr Janelle McAlpine (PhD), Clinical Midwife
Image by Tyler Olsen, used under license from Shutterstock.com