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Screening tests

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Screening tests are non-invasive and do not pose any risk to the baby but they will not give enough information to confirm whether the baby has a chromosome defect.

SOFT UK would like to thank Dr Lucy Kean (Consultant Obstetrician) and Lorna Parsons (Midwife), Nottingham University Hospitals

1st Trimester Combined Screening

Screening tests will indicate if a pregnancy is in a low or high risk category. Some couples choose not to have any tests. The National Screening Committee recommends that this should be offered as the preferred early screening test. It is performed between 11 and 13 weeks of pregnancy and uses ultrasound Nuchal Translucency (NT) measurement, plus a blood test to measure free beta hCG and PAPP-A.

Maternal Serum Screening Test - Triple or Quadruple Test

This is a blood test carried out between 15 to 20 weeks of pregnancy. Raised or lowered levels of certain chemicals in the blood can indicate an increased risk of Down syndrome.

Ultrasound

Pregnant women are usually offered 2 ultrasound scans. They cannot diagnose a chromosome abnormality but can look for structural abnormalities such as a heart defect or holoprosencephaly, and for chromosomal markers. These markers, or 'clue signs' can be seen in normal babies, but are more common in babies with a chromosome problem. Abnormalities seen on scan, or a cluster of chromosomal markers may alert medical staff to suspect a chromosome defect, but this can only be confirmed by an invasive diagnostic test.

Dating Scan

The first scan is called an early dating scan and it usually happens after 8 weeks of pregnancy.The purpose of the dating scan is to: 

  • Find out how many weeks pregnant you are
  • Check whether you are expecting more than one baby
  • Measure the size of the fluid area at the back of the neck, an area is called the nuchal translucency or NT
  • Check that the baby is growing in the right place
  • Check your baby's development
    Some abnormalities may also be detected at this scan such as neural tube defects, for example spina bifida.

Mid Trimester Anomaly Scan

The second ultrasound scan is often called a mid-trimester anomaly scan and it usually happens between 18 - 20 weeks of the pregnancy and screens for major structural anomalies. The objective of this scan is to:

  • Offer choice to women and their partners about their screening options and pregnancy.
  • Identify serious abnormalities when choices can be made whether to continue or terminate a pregnancy.
  • Identify abnormalities which may benefit from or need early treatment following delivery.

Before you agree to undergo this scan, you should be aware that the aim of this scan is to check your baby's development and that problems with your baby may be found. It is important to note that not all abnormalities can be seen on an ultrasound scan; just because nothing is picked up on the scan does not mean that your baby will have no problems or anomalies. There are things that the ultrasound scan cannot pick up. If the sonographer thinks that there may be a problem with your baby, you may be offered a further scan or an invasive diagnostic test such as chorionic villus sampling or amniocentesis. These tests look at your baby's chromosomes and can confirm whether he/she has a certain condition or not.

Fetal Cardiology

Many babies with trisomy 13 or trisomy 18 have heart defects and specialist centres can perform a detailed scan of the baby's heart during pregnancy.

Important

Improvements in antenatal screening mean you should ask your midwife or obstetrician for details of new tests that may be available. 

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