What Every Mother Needs to Know About Non-Invasive Prenatal Testing

30 November 2016
 Categories: Health & Medical , Blog


You may have heard from friends or your obstetrician about early blood tests that can give you information about your baby's health.  They go under a variety of names, but are collectively known as non-invasive prenatal testing or NIPT.  Blood is taken from the mother as early as 10 weeks and analysed to find small pieces of genetic information from the placenta. This is commonly called fetal DNA or cell-free fetal DNA.  The amount of DNA from different chromosomes is analysed to estimate the genetic makeup of the baby. This analysis can be used to give information about the risk of genetic conditions where a baby is born with an extra copy of one chromosome, such as Down Syndrome or Patau Syndrome. NIPT is highly accurate and simple to do, but it's important to understand what it can or can't tell you.

No answer is 100%

The NIPT is a screening test.  It gives the mum and her health professional the risk of the baby having a condition rather than telling them that the baby definitely does or doesn't have a particular syndrome.  NIPT will pick up Down Syndrome in 98% of babies with Down Syndrome but 2% of babies with is will have a normal test result. To confirm the baby does or doesn't have a syndrome a diagnostic test such as an amniocentesis or chorionic villus sampling (commonly called CVS) will be needed, however these tests are invasive and do pose risks to you and your baby.

Some pregnancies aren't suitable for a NIPT.

If you're having twins, triplets or quads then the NIPT test isn't going to be as accurate and may not give you useful information.  With more than one baby there's more than one set of genetic information and analysing this can lead to misleading results.  If your pregnancy is as a result of egg donation or if you've had certain medical treatments in the past then the test may not be accurate.  The test is usually done at around 10-14 weeks but in a small number of women not enough fetal DNA will be in the blood sample, so no result will be available.  In this case it can usually be repeated later in the pregnancy.

"So what are you having: boy or girl?"

Back when our grandparents were having babies there was only one way to find out whether the baby would be a boy or girl: wait for it to be born and sneak a peek between the baby's legs! In the 1980s grainy ultrasound images gave some mums to be information about their baby's sex and by the late 1990s most women found out whether they were expecting a boy or girl at the mid-pregnancy anatomy scan. Now NIPT can be used to find out whether the baby is a boy or girl while you're still in the first trimester.  Analysing the fetal DNA can show whether the baby is a boy with XY chromosomes or a girl with two X chromosomes.  Around 1 in 200 results will be incorrect, but the test does offer an early way to find out what side of the children's clothing department you'll be frequenting!

Pregnancy can be a nerve wrecking time and testing such as NIPT can help by giving parents more information.  At the moment there isn't an Australian recommendation for who NIPT should be offered to so it's important to discuss your unique pregnancy and situation with your obstetrician.