Screening Tests in Early Pregnancy

Combined Screening tests in Early Pregnancy

This involves a combination of various screening tests for Downs and Spina Bifida

  • Ultrasound Scan includes your Dating Scan
  • Blood test
  • Testing between 8 and 14 weeks
  • Non Diagnostic, gives risk factor only.

These are offered in pregnancy when you book with your midwife. You will be offered a normal dating scan but additionally will be offered combined screening tests in pregnancy so that only one scan is needed.

The combined screening tests in pregnancy involves an ultrasound scan called a Nuchal Translucency test or NT Measurement, where the sonographer will measure the pad of fat on the back of the baby's neck, which may be an indicator for downs syndrome if the pad of fat is thickened.

A blood test is also taken which measures 2 pregnancy associated chemicals.

All this information is sent off to a lab where they do the testing and the results of this test is calculated to give a risk factor only of your chances of having a baby with downs and spina bifida.

You may have a Low risk or High risk result. If you have a low risk result then you will not be offered further screening.
If your risk factor comes back high, then you will be informed by the hospital or midwife. You will then be offered more tests such as the Amniocentesis which is gives a true diagnosis of any genetic abnormalities. This is explained below.

Serum Screening only

  • Normally only a Blood test with no combination of Ultrasound Scan
  • Testing ideally between 16 - 19 weeks
  • Non Diagnostic - Gives risk factor only

This is just a simple blood test offered at 16 weeks of pregnancy and it is usually done if the sonographer is unable to get the Nuchal Fold measurement clearly, which can happen, or the woman is further along in her pregnancy than expected and past 14 weeks.

The Blood test is sent to the lab with information such as age, weight and other measurements taken from the dating scan and a risk factor is generated.

Again if your risk factor comes back high, then you will be informed by the hospital or midwife. You will then be offered more tests such as the Amniocentesis which is gives a true diagnosis of any genetic abnormalities. This is explained below.


This is offered to women in pregnancy who have a high risk result from the combined or serum tests.

The procedure itself involves the Doctor (Obstetrician) passing a very fine needle through the woman's abdomen to collect a sample of the amniotic fluid around the baby. This procedure is performed by a senior obstetrician like a senior registrar or Consultant and they use an ultrasound scanner so that they can pass the needle into the space around the baby and not near the baby.

The sample of amniotic fluid is then sent away to be tested at the lab and the result gives a definite result of YES or NO to your baby having downs or spina bifida.

Nationally, the procedure itself carries a 1:200 chance of miscarriage. You would need to contact your local hospital for their own statistics.

How an Amniocentesis is Performed


Screening - What do I need to Consider?

  • Combined and Serum screening comes back with a risk factor only not a diagnosis
  • You need to think about the "what if's" meaning that if you went ahead with any screening if the result was high risk result, then what would you do with that information, would you go ahead with the amniocentesis or not?
  • The amniocentesis carries a 1:200 chance of miscarriage, a woman could go through all the testing and then miscarry a perfectly healthy baby.
  • What happens if your baby does have any genetic disorder which can affect the baby's life, would you continue with your pregnancy or not? It comes down to personal feelings and circumstances with the woman and her partner.
  • If you don't wish to continue with your pregnancy, then depending on your gestation you may need to be induced to deliver which can be quite distressing.

This is absolutely personal choice, however there are women who just want to have the initial combined screening and end up having to make harder decisions further along the chain as they have not considered any consequences. This is about informed choice and the more information you have then you can make your own choices.

Speak to your midwife or doctor if you are unsure, if you rather not know then don't start any screening.

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