First trimester genetic testing: what you need to know

first trimester genetic testing

One of the most important decisions you’ll be faced with in your first trimester is which, if any, genetic testing you wanted to undertake in early pregnancy.

Genetic testing will tell you if your baby has an increased risk of certain health conditions, like Down syndrome.

These tests are optional, and there are women who opt not to undergo any form of genetic tests during their pregnancy. However, the results can help you plan ahead if you’re at increased risk of having a baby with a specific condition.

First-trimester testing

The most common genetic test conducted in the first three months of pregnancy is the combined screening test. This test combines results from a blood test and ultrasound, to decipher the chance of your baby having Down syndrome or other abnormalities.

Somewhere between nine weeks and 14 weeks your blood will be taken, with the levels of two hormones checked. This blood test is called maternal serum screening.

An ultrasound on your baby will be taken between 11 weeks and 13 weeks, six days to check the thickness of the fluid behind your baby’s neck. Known as the nuchal translucency, this area is usually larger in babies with Down syndrome.

The results of both the blood test and ultrasound are then combined, taking into account your age and weight, and your baby’s gestation to come up with the risk of your baby having Down syndrome, Trisomy 13 and Trisomy 18. Generally, you should get these results back in a week, and your doctor will let you know the results.

first trimester genetic screening

What are the tests for?

Down syndrome – this is known as trisomy 21, and is an intellectual disability that can vary from person to person. It can also cause heart defects or problems with sight and hearing.

Edward syndrome – known as trisomy 18, it’s a condition that causes intellectual disabilities, as well as heart and digestive system defects. Sadly, many babies who are born with Edward syndrome don’t live longer than a few weeks.

Neural tube defects – these include anencephaly (where the brain doesn’t develop properly and the baby can’t survive) and spina bifida.

It’s important to remember …

  • The test won’t tell you if your baby does have Down syndrome, but rather give you a risk factor. This can range from ‘not an increased risk’ – which means the chance of your baby having Down syndrome is low, to ‘at increased risk’ – which means the risk of your baby being affected is more than 1 in 300.
  • One in 25 women will get the news that they are ‘at increased risk’. This doesn’t mean the baby has Down syndrome.
  • If your doctor does inform you that you are ‘at increased risk’ there is further testing that can confirm if your baby has Down syndrome in the second trimester.

Sources: Better Health and Healthy WA

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