Your pregnancy scans & tests explained

Routine blood tests and ultrasound scans are a vital part of determining the health of your pregnancy – from that initial scan where you can first see your baby, through to all the different blood tests you undergo; it is all part of the bigger picture of monitoring both your health and your baby’s health. Here in Aotearoa New Zealand there are a set of standard tests that pregnant women can be offered as part of your antenatal care. To give you a good idea of what to prepare for we have broken these down for you below.

First Trimester Blood Tests:

The first trimester blood tests in New Zealand are usually organised when you first see your GP at the beginning of your pregnancy. These tests are done to check your blood group, Rhesus factor and antibodies, haemoglobin, iron levels, immunity to rubella, and your hepatitis B, hepatitis C, HIV and syphilis status. It is a simple blood test performed at your local laboratory. The results will be sent to the practitioner who requested the test.

Nuchal Translucency Scan and Combined First Trimester Screening:

Pregnancy ultrasounds use sound waves to create an image of your growing baby in your womb. They are painless and non-invasive. There is no radiation involved, and they typically take between 15-30 minutes to complete.

At 12 to 13+6 weeks of pregnancy, a Nuchal Translucency Ultrasound Scan can be performed to assess the potential risk of Down Syndrome (Trisomy 21), Trisomy 13 and 18, and other Syndromes. This is usually your first pregnancy ultrasound scan and measures the thickness of the fluid at the back of the baby's neck. The width of the baby’s neck is bigger with Syndromes and abnormalities. If your baby is in a good position, the sonographer can also check how the baby's organs are developing.

For a complete risk assessment, a blood test needs to be performed between 9-13 weeks of pregnancy. This blood test measures placental markers. This combination of an ultrasound and blood test is called the MSS1 screening test or CFTS (combined first trimester screening). Your result will come back as high or low risk. Those who have a high-risk screen will be offered further testing.

If the decision is made not to have the above screening test it is still important to have an ultrasound around 12 weeks of pregnancy to confirm the pregnancy is viable, inside the uterus (that is not an ectopic pregnancy) and to check for twins or even triplets. This ultrasound can also help determine that your baby is developing normally.

The Nuchal Translucency scan and the 20 week anatomy scan are performed at Specialised Radiology Practices.

Second Trimester Blood Tests:

If the first trimester screening test is missed and a screening test is still desired blood tests can be done between 14-20 weeks of pregnancy. These results are not combined with an ultrasound scan and are less sensitive than the first trimester screening bloods for detecting Down Syndrome and other Syndromes. These can be done by your local laboratory and test results will be sent to the practitioner who requested the test.

Anatomy Scan:

At around 20 weeks, an anatomy ultrasound scan is performed to check on your baby's growth and development. This scan checks for any anatomical differences in the baby's organs, limbs, and other body parts. The placenta, umbilical cord and uterine anatomy is also reviewed. The anatomy scan is a longer ultrasound scan and can take around 45 minutes to complete. If there are any concerns, you will be offered further scans or further investigations at your local hospital.

Gestational Diabetes Screening (Polycose test (GCT) and Glucose tolerance test (GTT):

Between weeks 26-28, a glucose test is performed to screen for gestational diabetes. This test measures how your body processes sugar (glucose), and if there are any issues, steps can be taken to manage the condition.

The test involves drinking a glucose solution and then having blood drawn at specific intervals to measure blood glucose levels. The test typically takes 1-2 hours to complete and can involve fasting beforehand.

At the same time as this blood test, your Haemoglobin and Iron stores are checked. If you’re low in red blood cells, which is also known as anaemia, this will be diagnosed and treated, usually with iron tablets.

Group B Streptococcus (GBS) Test:

Around 36 weeks of pregnancy, a GBS test can be done to check for the presence of the bacteria Group B Streptococcus around the birth canal. This test is done via a self-collected vaginal and anorectal swab, and if the test is positive, antibiotics can be given during your labour to reduce the risk of infection in your baby.

Third Trimester Blood Tests:

Around 36 weeks of pregnancy, your Haemoglobin and Iron status is checked again so any anaemia can be diagnosed and treated before birth.

Additional Ultrasound Scans:

If there are any concerns about the baby's growth, position or placental location, an ultrasound scan may be done at any stage in your pregnancy. In the later stages of your pregnancy, this can be helpful to assess and determine the best method for birth.

High-Risk Pregnancies:

For expectant mothers who have high-risk pregnancies, additional testing may be required. High-risk pregnancies may include pregnancies in women over 35, multiple babies, or pregnancies with other health concerns. Additional testing may include more frequent ultrasounds, antenatal diagnostic testing, or other types of monitoring.

Other Tests:

NIPT (non-invasive prenatal testing)

The NIPT test can be done instead of the MSS1 or CFTS first trimester screening test. Usually, there is an additional fee for this test. It is a screening test for some chromosomal abnormalities in pregnancy. It is able to screen for Down Syndrome and other Syndromes more accurately. It can usually be performed from 10 weeks of pregnancy onwards. If this test comes back as high-risk you will be offered further investigations.

Prenatal genetic carrier screening (before pregnancy)

Pre-pregnancy genetic testing (carrier testing) can be done before you become pregnant. This test includes genetic carrier screening to identify whether you or your partner carry genetic conditions that could be passed on to your baby. This testing may be recommended based on your ethnic background, family history, or other factors. Some conditions checked for include cystic fibrosis, spinal muscular atrophy and sickle cell anaemia. This is organised as part of preconceptual counselling to determine if any of these tests are relevant to you.

Antenatal genetic testing (while pregnant)

Antenatal genetic testing may also be offered to expectant mothers who have a family history of genetic disorders, or who are carriers for certain conditions, or who have a high-risk result on their first trimester screening test or ultrasound scan.

These are known as diagnostic tests and include a CVS (chorionic villus sampling) or amniocentesis. These are performed by Specialist Obstetricians who are specifically trained in CVS and amniocentesis.

The amount of testing and scanning may seem overwhelming, there are lots of appointments to try and fit in as well as preparing for a baby. However your LMC will manage this and help you schedule them over the course of your pregnancy. These tests are designed to identify potential issues, ensure that both you and baby receive appropriate care, and overall help keep you and your baby safe during pregnancy.

At Wellington Obstetrics, we have the best ultrasound services in Wellington, Wellington Ultrasound, as our neighbours, and we can conduct many of the other testing you may need in house. We’ll help guide you through your appointments and be on hand for any questions or concerns you may have.

Get in touch to meet our team today

Pregnancy Scans & TestsSarah WrightJune 1, 2023