Conditions & Treatments

First Trimester Screening & Non-Invasive Prenatal Testing - Treatments

WHAT IS FIRST TRIMESTER SCREENING (FTS)?

First trimester screening is performed between 11-14 weeks of pregnancy when the baby measures between 45 - 84mm in length. There are two parts to the test and a computer software will combine the results with the mother’s age to give an estimate of the risk for Down syndrome.

The two components of FTS are -

An ultrasound scan to measure the nuchal translucency (NT), which is the amount of fluid at the back of baby’s neck. NT measurement can detect 80% of babies with Down syndrome if performed alone. The ultrasound scan will additionally allow your doctor to screen for physical abnormalities in the baby.
A blood test to measure the level of two proteins - pregnancy associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG) - in the mother’s blood. This improves the detection rate for Down syndrome to 90% when performed in combination with the ultrasound scan.

Figure 2. Nuchal translucency (seen between the two white + markings) of the fetus.

Figure 3. Thickened nuchal translucency (measurements within the 2 white + markings) in a baby with Down Syndrome

You may opt to do (1) alone or both (1) and (2) together, which is known as the combined test.

Table 1: Summary of currently available screening tests for Down Syndrome

HOW DO I PREPARE FOR FTS AND WHAT CAN I EXPECT?

It is important to keep to your scheduled appointment, as changing the appointment date may result in the baby being too small or too large for the FTS to be accurate. There is no need for any special preparation for FTS. You can eat and drink on the day of the test.

The ultrasound scan will usually be performed through the abdomen. In some cases, accurate measurement of the NT cannot be achieved because of the position or size of the baby. If the baby is <45mm in length, you will be given another appointment for repeat scanning. If the baby is >84mm in length, alternative methods of screening will be discussed with you.

ARE THERE ANY RISKS IN PERFORMING FTS?

No, FTS will not cause any risk to your pregnancy.

HOW DO I INTERPRET MY FTS RESULTS?

Your results will be reported in the form of an estimated risk.

For example –

Mdm A undergoes FTS. Her estimated risk of having a baby with Down syndrome is 1 in 10. This means that among 10 similar pregnancies with the same ultrasound and blood protein measurements, 1 pregnancy will eventually result in the birth of a baby with Down syndrome, while the other 9 pregnancies will result in the birth of babies unaffected by Down syndrome.

WHAT IS A HIGH-RISK RESULT AND WHAT HAPPENS IF MY RESULTS ARE HIGH-RISK?

A “high-risk” or positive result is when the chance of the baby having Down syndrome is higher than 1 in 300 on FTS. Please remember that FTS only tells you the chance of the baby having Down syndrome, and does not confirm

if the baby has Down syndrome or not. Around 5% of women doing FTS have a false-positive result, meaning that

the test result is positive but the baby does not actually have Down syndrome.

Your doctor will discuss your results with you and explain your options. These may include doing another screening

test such as NIPT, or performing a diagnostic test such as chorionic villus sampling or amniocentesis. Diagnostic tests are the only way to confirm the diagnosis but are associated with a small risk of miscarriage of about 1%.

WHAT IS A LOW-RISK RESULT AND WHAT HAPPENS IF MY RESULTS ARE LOW-RISK?

Most women who undergo FTS have a low risk result. This does not mean that the baby definitely does not have Down syndrome, but suggests that the likelihood of the baby being affected is small.