It is important to see your doctor promptly after pregnancy is confirmed. This is because some tests for foetal abnormalities are carried out before you have your first pre-natal appointment. There are two categories of tests. Screening tests assess the risk of abnormality, while diagnostic tests determine for certain whether the foetus has a chromosomal abnormality or structural defect, such as spina bifida. Some diagnostic tests are invasive and hence carry a risk to the foetus. For example, CVS and amniocentesis both carry a risk of miscarriage of around one per cent, while for cordocentesis it is put at one to two per cent. However, the level of risk depends on the operators’ skill.
A non-invasive procedure that offers a window into the womb. If you experience bleeding or abdominal pain, or have a history of miscarriage or ectopic pregnancy, you may be offered a scan as early as six weeks.
- Dating scan - in some areas, a scan is offered at 11 – 13 weeks to date the pregnancy and to pick up possible developmental problems.
- Nuchal translucency scan - this measures the fluid at the back of the baby’s neck, and is sometimes looked at alongside a maternal blood sample. This can assess the baby’s risk of having Down’s syndrome, and is usually offered to women over 35 (the risk of Down’s increases with age).
- Fetal anomaly scan - offered routinely at 18 – 20 weeks to check for abnormalities, such as heart defects, and to confirm EDD to within ten days.
Non-invasive blood tests that measure levels of AFP (alphafetoproten), a hormone produced in early pregnancy, along with other marker to gauge the risks of Down’s syndrome or neural tube defects such as spina bifida. The tests are usually carried out at around 16 weeks, and the results are known within two to three days. If the risk is greater than one n 250, further testing, such as ultrasound or amniocentesis, will be offered.
Chorionic villus sampling (CVS)
An invasive test that is usually only offered to women considered high risk. It tests for chromosome abnormalities and inherited disorders by taking a tissue sample from the placenta. It is carried out at 11 weeks, and results take five to seven days.
A sample of blood is taken from the foetal vein in the umbilical cord to test for chromosome disorders and inherited disorders. It can also detect infections such as toxoplasmosis and rubella. It cannot be performed before 18 weeks, and results take a week to arrive.
At around 16 weeks, cells are taken from the amniotic fluid surrounding the baby to test for Down’s syndrome, spina bifida and cystic fibrosis, plus other disorders. Results can take up to four weeks. Some hospitals offer more rapid testing methods with results in two to three days, so do ask. A faster test (Amnio Q-PCR/Amnio + FISH) can rapidly diagnose Down’s. Turner’s and Edwards’ syndromes, but isn’t widely available. Alternatively this test, like standard amniocentesis, can be done privately.