Antenatal Screening Explained
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Screening tests are non-invasive tests that can be offered to all pregnant women. They are NOT diagnostic; they help to identify women who have an increased risk of having a baby with either Down’s syndrome of Neural tube defect.
Down’s syndrome
Down’s syndrome is caused by an extra chromosome 21, sometimes referred to as trisomy 21, giving a total of 47 chromosomes. This is a genetic accident that occurs at conception.
Risk of Down’s syndrome
Maternal Age
Less than 25 Years
Risk of Down's Syndrome
1:1500
Maternal Age
30Years
Risk of Down's Syndrome
1:900
Maternal Age
40Years
Risk of Down's Syndrome
1:110
All Maternal Age
All
Risk of Down's Syndrome
1:800
Neural tube defect
There are two kinds of Neural tube defect:
- Spina Bifida
- Anencephaly
Babies with Spina Bifida have an opening in the bones of their spine, which can result in damage to the nerves controlling the lower part of the body. This can cause some weakness and paralysis of the legs and sometimes bowel and bladder. Babies with spina bifida are more likely to have a collection of fluid on the brain called hydrocephalus which can lead to mental disability.
Here at the Liverpool Women’s Foundation Trust we offer the Triple Test to all women and this is free on the NHS. This is a simple blood test at 15- 22 weeks and along with your age will calculate the risk of your baby having Down’s syndrome or neural tube defect.
The Triple test cannot tell you if your baby has or has not either of these problems but will indicate if you should be offered diagnostic testing.
The Triple test measures 3 biochemical markers in your blood:
- AFP – Alpha Feto Protein
- hCG – Human Chorionic Gonadatrophin
- uE3 – Unconjugated Oestriol
In babies where the baby has Down’s syndrome the hCG is usually higher than average and the uE3 and AFP lower.
If the AFP is raised then this can indicate the baby may have a nueral tube defect. If this is the case then you will be asked to attend the FMU for a detailed scan with one of the Fetal Medicine team specialists./general_21.jpg)
Results of the Triple Test
If the test shows that your risk of having a baby with Downs syndrome is lower than 1:250 then you will be low risk . Low risk does not mean NO risk at all.
If your risk is greater than 1:250 then you will be high risk.
If you have a high risk result you will be sent an appointment for a face to face discussion of your result with one of the FMU midwives. ALL screening tests and diagnostic tests are optional. The aim is for you to receive clear and concise information allowing you to make an informed choice.
