Skip to content

Prenatal diagnosis

Prenatal screening

There have been a few changes in recent years to how we assess the health and development of babies during pregnancy. There are three main steps to ensuring the health and wellbeing of the baby. These are:

  • An early dating scan to confirm the pregnancy.
  • The first trimester screening by ultrasound and blood tests, to assess the risk of some chromosomal conditions like Down syndrome.
  • The morphology scan between 19 and 20 weeks to check the baby’s heart, brain, skeleton and overall development.

Dating scan – before 10 weeks

To confirm and assess your pregnancy location, viability and size, as well as confirm a single or multiple pregnancy. The size of the baby and heart rate will also be checked. You will be given an expected due date (EDD) based on your dates, the baby’s size and stage of pregnancy.

First trimester screening at 10–14 weeks

At this stage of pregnancy your doctor may suggest that you have your baby assessed for conditions that can affect the health and development of the baby. For example, Down syndrome. These tests are completely optional.

Option 1

At 10-14 weeks

Non-invasive Prenatal Test (cell free fetal DNA test)

You will have a scan followed by the NIPT blood test. The test counts fragments of DNA in the maternal circulation. NIPT detects more than 99% of Down syndrome, as well as some other Trisomies. It can also determine the fetal sex and some sex chromosome abnormalities.

At 12-14 weeks

Early structural scan

This scan detects about 50% of major structural abnormalites in the baby. This ultrasound also includes looking for a thick nuchal translucency, which can be associated with congenital heart defects and skeletal problems.

Option 2

At 12-14 weeks

Nuchal Translucency scan with free BHCG and PAPP-A blood test

This ultrasound measures the nuchal translucency (NT) thickness and nasal bone. A few (usually five) days prior to the scan you are required to have the free BHCG and PAPP-A blood tests. Together the scan measurements and blood test calculate the risk of the baby having three common chromosomal conditions. It detects 95% of Down syndrome and about 50% of major structural abnormalities.

If your results show a High Risk of Down syndrome, or if you would simply like added reassurance, you can proceed with the NIPT blood test on the day or consider an amniocentesis or a chorionic villus sampling test.

Pre-Eclampsia screening

If your doctor has requested pre-eclampsia screening, your blood pressure and uterine artery flow studies will also be measured on the day of the scan.

Morphology scan 19–20 weeks

The fetus is measured to assess size and growth. Also, this scan records the position of the placenta, checks the volume of the fluid around the baby and assesses the baby’s developing organs and complex structures like the heart and brain, which are too small for detailed examination earlier. If required, the fetal gender can be determined 99% of the time. The cervical length is measured by transvaginal examination to predict preterm birth.