Foetal diagnostics - ultrasound, combined test and NIPT

When it comes to foetal diagnostics, most people are familiar with the ultrasound exam. But other common exams include the combined test and NIPT – where you go in deeper to obtain more information about the baby.
These names and abbreviations can be a little confusing, so remember that you can always contact your doctor or midwife for more information. They can explain more about the various foetal diagnostic methods, how they work and what answers they might offer.

Ultrasound exam

The ultrasound exam is the most common and is offered and recommended to all pregnant people around week 18 to 20. An ultrasound shows how long you’ve been pregnant and how the pregnancy is developing. An ultrasound is simple and painless; it consists of high-frequency sound waves sent through the abdominal wall into the uterus. Sometimes, especially early in the pregnancy, an ultrasound exam can be done vaginally, from inside the vagina.
The exam results in two or three-dimensional images of your baby that enable a thorough medical observation, because the finest details and structures of the foetus can be discerned.

Via ultrasound, you can see:

• Baby’s size.
• Baby’s heart activity.
• How the pregnancy has developed.
• How long you have been pregnant.
• How many foetuses are in the womb.
• The quantity of amniotic fluid.
• The position of the placenta within the uterus.
• Whether the foetus has all of its vital organs.
• Whether the foetus has any visible abnormalities.

So, what you can see forms the basis for everything from how to plan the delivery to how many prams you need. Sometimes you may have additional ultrasound exams, so-called growth ultrasounds, to see if the baby (or babies) is growing along the curve. When this exam is done can vary based on where you live. It is also important to know that an ultrasound doesn’t show everything, but if something is detected that indicates a deviation, you will be offered additional foetal diagnostics.

Ultrasound should be medically justified

Ultrasound involves high-frequency sound waves, and in Sweden, the Swedish Radiation Safety Authority determined that foetuses should only be exposed to ultrasound for medical purposes – such as seeing how long the pregnancy has been underway and possibly following up to ensure the baby is growing properly. To be on the safe side, this means that you should not make videos, take pictures, or search for a penis or vagina for any reason other than a medical purpose.

Combined ultrasound and blood test

A combined test has two parts: a blood test is taken to measure the quantity of pregnancy hormones. Then a special ultrasound exam is done during weeks 11–14 to measure the thickness of the skin at the back of the baby’s neck. The results of these tests indicate the likelihood that a foetus has Down’s syndrome or other, rarer chromosome abnormalities.

The result of the combined test is only an assessment of likelihood; it is not definitive proof. If the combined test suggests an elevated risk, you can go on to NIPT (non-invasive prenatal testing), amniocentesis or placenta sampling. The guidelines for who is offered a combined test vary from place to place – if this feels important to you, then talk about it with your doctor or midwife.

NIPT – blood test that shows chromosomes

Non-invasive prenatal testing, or NIPT, is a blood test taken from the pregnant person from week 10. This reliable, risk-free test shows the baby’s DNA in the blood, which can indicate whether the foetus has certain chromosome abnormalities. If abnormalities are detected, a sample of the placenta or amniotic fluid is needed for a definitive answer. NIPT is not offered to everyone and different places have different policies. But this test might be offered to pregnant people whose combined test showed a high likelihood of a chromosome abnormality. NIPT has largely replaced the older and less precise NT scan.

Amniocentesis

If previous tests demonstrated an increased risk that the foetus has a chromosome abnormality, you can go on to amniocentesis. For this test, a doctor inserts a thin needle into the uterus and sucks up a little bit of amniotic fluid for analysis. This test can’t be done before week 15 and it is important to know that it can increase the risk of miscarriage by about 0.5–1%.

Placenta sampling

An alternative to amniocentesis is placenta sampling. Placenta sampling is offered to people with certain known hereditary diseases or whose test results have shown an increased likelihood that the foetus has a chromosome abnormality. Since this test can be done as early as week 11, placenta sampling may be recommended if a doctor thinks it’s important to have early confirmation. The test uses essentially the same method as amniocentesis, and thus results in the same slight increase in the risk of miscarriage.

Other tests to monitor the baby

A few other tests can also be done to monitor the baby in your belly. These include blood tests on the mother to check for antibodies to blood types other than the mother’s own, or analyses of antibodies to various viral diseases – which may be important to know. If the baby does not seem to be growing as it should be later in pregnancy, then in addition to the growth ultrasound, blood flow in the umbilical cord might be measured to see if the baby is getting the necessary oxygen and nutrients.

Why do you want to know?

There are various reasons why you might want to run foetal diagnostics, and there is no right or wrong approach. It may offer relief and a sense of security to know that everything looks good, but it could also lead to worry about having a difficult choice to make if the foetus does indeed have a chromosome abnormality or another abnormality. It may be important to mentally prepare for life with a child being different than what you had originally imagined. You might also feel like the tests don’t matter: your baby will still be your baby and loved exactly as they are. It is important to consider what you want to do, because these tests are voluntary. It may be wise to really think through what you want to know and why, and at the same time, you might have to think about how you may react if the test result isn’t what you had hoped for. Consider talking to a therapist (which you may be entitled to in many places), including as a partner, if you’re struggling to decide whether to have these tests done.

Please note that all information above is based on Swedish recommendations.