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combined screening in pregnancy

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What is combined screening?

Combined screening is a test offered to all women between 11 weeks and two days and 14 weeks and one day to help identify pregnancies that have a higher chance of being affected with one of three chromosome conditions: Down’s syndrome (trisomy 21), Edward’s syndrome (trisomy 18) and Patau’s syndrome (trisomy 13).

It is a screening test, which means it will not tell you definitely whether your baby has any of these conditions. This test can only tell you the chance of your baby being affected. You can then use this information to help decide whether to go on and have a diagnostic (invasive) test. This test is optional: it is your choice whether to have this test or not.

Your midwife will ask if you would like screening for:

  • All three conditions (one risk for Down’s syndrome and one risk for Edward’s & Patau’s syndromes combined).
  • Down’s syndrome only.
  • Edward’s and Patau’s syndromes (one risk for both conditions).
  • None of the conditions.

How can you tell if my baby definitely has Down’s,
Edward’s or Patau’s syndrome?

Only an invasive diagnostic test such as Chorionic Villus Sampling (CVS) or Amniocentesis can tell you for sure if your baby has one of these conditions. However these tests carry a risk of miscarriage of around one in a 100 (1%). Therefore you need to consider carefully whether you want to have a diagnostic test and the results from Combined Screening may help with this decision.

More information about diagnostic tests is available in the leaflet CVS and Amniocentesis or you can speak to your doctor or midwife.

How does Combined Screening identify pregnancies at
higher chance of Down’s, Edward’s or Patau’s syndrome?

It is called Combined Screening because it combines information from an ultrasound scan and blood test to work out the chance of your baby having a chromosome condition. The ultrasound scan checks your dates and measures the amount of fluid behind the baby’s neck, called the nuchal translucency.

An increased amount of fluid is more likely in babies with chromosome conditions. The blood test is taken from you after the scan. It measures the levels of two substances found in your blood during pregnancy which may be altered if the baby has a chromosome condition.

Other factors which can affect the result are also taken into account: these include your family origins, age, weight, smoking history, pregnancy history and medical history.

When will I get the results?

This depends on whether your result is assessed as a higher or lower chance for the conditions you chose to be screened for.

A lower chance result (also called a low risk result).

Any result below 1 in 150 is considered to be a ‘lower chance’. (This is less than 0.7%, such as 1 in 200, 1 in 850, 1 in 4400 etc.). The bigger the number, the lower the risk. This does not rule out the condition in your baby but means it is less likely. We will write to you within two weeks of having the test if you have a low chance result. If you have not received your result by this time, please contact the screening midwives (contact phone number available in the Further Information section).

A higher chance result (also called a high risk result).

Any result of 1 in 150 or higher (such as 1 in 120, 1 in 50, 1 in 8 etc.) is considered to be ‘higher chance’. The smaller the number, the higher the risk. In these cases, a specialist midwife will call you, usually within three working days. We will offer you an appointment to discuss the result in more detail and discuss whether you want to have a diagnostic test. Remember, a higher chance result does not mean there is definitely a problem with your baby and most women given this result will go on to have a healthy baby.

How reliable is Combined Screening?

Combined screening identifies about 80% (eight out of ten) of babies with Down’s syndrome.

What happens if I am over 14 weeks and one day
pregnant at scan?

If you are over 14 weeks and one day at the scan it is too late to have combined screening. However we can offer you another screening test, called the ‘quadruple test’. This is a blood test that measures the amount of four substances in your blood to work out the chance of the baby having Down’s or Edward’s syndromes. Unfortunately it is not possible to offer women who book after 22 weeks of pregnancy any screening tests for chromosome conditions.

Can Combined Screening be used if I am having twins?

Yes, Combined Screening can be used if you are expecting twins.

Can any other abnormalities be identified by Combined Screening?

If the amount of fluid on the baby’s neck is increased at 3.5mm or more, this may indicate a rarer chromosome, genetic or structural problem in the baby. In such cases we would discuss this with you and offer a detailed heart scan as well as invasive testing. Finding an increased amount of fluid does not mean there is definitely a problem.

It is important to remember that no test can guarantee that your baby will be free of all abnormalities.

Further information

To discuss any of these tests or your results in more detail you might find it helpful to call our specialist screening midwives on 07876 357 423. The following organisations may also be of help

Down’s Syndrome Association.
Provides information and support for people with Down’s syndrome, their families and carers.
Helpline 0333 1212 300.

Support organisation for trisomy 13 and 18.
Helpline 0121 351 3122.

Antenatal Results and Choices (ARC)
National organisation providing support and information about screening tests, test results and diagnosis of fetal abnormality.
Helpline 0845 077 2290.

If you have vision, mobility or access issues please contact the specialist screening midwife team on 07876 357 423 for further information. You can also call the midwives at the hospital in the antenatal clinic on

Royal Sussex County Hospital.

Telephone 01273 696955 (ask for antenatal clinic).

Princess Royal Hospital.

Telephone 01444 441881 (ask for antenatal clinic).

This information is for guidance purposes only and is in no way intended to replace professional clinical advice by a qualified practitioner.

This article is intended for patients receiving care in Brighton & Hove or Haywards Heath.

Publication Date: May 2018

Review Date: October 2022

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