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Types of Screening Tests

Combined Test

Between 11 and 13 weeks of pregnancy, a combination of the nuchal scan measurement (see Nuchal Scan below) and a blood sample from the mother which measures the concentration of two serums: pregnancy associated plasma protein-A (PAPP-A), and free beta human chorionic gonadotrophin (Free beta hCG); together with the mother's age, are used to estimate her chances of having a pregnancy with Down's syndrome. If the chance is more than 1 in 250 (although this does vary with different hospitals) a diagnostic test, such as CVS, will be offered.

Integrated Test

The integrated test is performed in two stages. In the first stage, at around 12 weeks of pregnancy, a blood sample is taken from the mother which measures the concentration of serum pregnancy associated plasma protein-A (PAPP-A) and a nuchal scan is also carried out. The second stage involves a second blood sample which is ideally taken at 15 or 16 weeks of pregnancy. Only after this second stage is a statistical result given. This blood sample measures four serum levels - alpha feto protein (AFP), unconjugated oestriol (uE3), free beta human chorionic gonadotrophin (freeß-hCG) and inhibin-A (inhibin). The measurement of the total six markers together with the mother's age are used to estimate her chances of having a pregnancy with Down's syndrome. Women with a chance greater than 1 in 100 are offered amniocentesis.

Nuchal Scan

Between 11 - 13 weeks of pregnancy the fluid at the back of the baby’s neck, the nuchal translucency, is measured. By combining the mother’s age with information from the scan an individual statistical chance of a chromosome abnormality can be given for that particular pregnancy. If the chance is more than 1 in 250 (although this does vary with different hospitals) a diagnostic test, such as CVS, will be offered.

Triple Test

This test has many names - you may hear it called the Leed’s test, the Bart’s test, the double test or the blood test. A sample of blood is taken usually between 16-18 weeks of pregnancy. The stage of pregnancy is best estimated by an ultrasound dating scan. The number of substances measured will vary according to hospital policy but they will be a combination of alpha-fetoprotein (AFP), uncojugated oestriol (uE3) inhibin-A (inhibin) and free beta human chorionic gonadotrophin (free ß -hCG). The concentrations of these substances are used together with the mother’s age to estimate her chances of having a pregnancy with Down’s syndrome. The level of AFP is also used to determine if there is an increased chance of spina bifida or anencephaly. Women with a chance greater than 1 in 250 (although the figure does vary at different hospitals) are offered amniocentesis. One in every 20 women will be given a chance greater than 1 in 250.

Screening for sickle cell and thalassaemia

This screening involves a simple blood test and questions about your family origins and those of the father of the baby. The haemoglobinopathies are common inherited blood conditions, they mainly affect people who have originated from Africa, the Caribbean, the Middle East, Asia and the Mediterranean, but are also found in the northern European population. More information can be found at the Sickle Cell Society and the UK Thalassaemia Society.

Ultrasound Scanning

This is a technique used routinely in most hospitals to monitor the growth and development of the baby before birth. Scans can be used as a means of screening in pregnancy by identifying ‘markers’ which are indications of chromosomal abnormalities.