TIMING OF ANTENATAL SCREENING AND DIAGNOSTIC TESTS
Fetal viability ultrasound scan
6 – 10 weeks
This scan is usually done in an early pregnancy unit to check the pregnancy is progressing as expected.
Dating ultrasound scan
9-14 weeks
The sonographer will take measurements of the baby to estimate the number of weeks the baby is and to predict when you might be expected to give birth to your baby. Very occasionally the sonographer may find that the baby is not developing as expected.
Sickle cell & thalassaemia blood test
Ideally before 10 weeks (but can be done later)
This test is usually offered to women whose ethnicity means there is a chance they carry a gene for sickle cell disorder or thalassaemia and may risk passing it on to the baby. If the test suggests a woman carries a gene, the father of the baby will be offered a test.
Infectious diseases blood test
8 – 12 weeks
You will be offered tests for HIV, syphilis and hepatitis B.
Combined screening test for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome
11 – 14 weeks
This test combines maternal information with measurements taken from an ultrasound scan and a blood test. All the information is put in a computer to calculate the chance of a baby having one of the conditions.
Quadruple blood screening test
14 – 20 weeks
If you are too late for, or, for some reason, unable to have the combined test, you will be offered a test called the quadruple blood screening test. This only screens for Down’s syndrome and is not as accurate as the combined test.
Non-Invasive Prenatal testing (NIPT)
From 10 weeks onwards
If you are in England, Scotland or Wales and receive a higher chance combined or quadruple test result, you will be offered NIPT. This blood test gives a more reliable prediction of the likelihood of the baby having Down’s syndrome, Edwards or Patau’s syndrome than combined or quadruple screening. It does not give a definite yes/no answer.
Chorionic villus sampling (CVS) diagnostic test
11 – 14 weeks
If your Combined screening or NIPT gives a higher-chance result you will be offered a CVS. This will tell you for certain whether or not your baby has Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. It might also be offered if anomalies are seen on a scan.
Depending on the tests done on the sample taken by the CVS, other chromosomal or genetic conditions can be diagnosed. There is a 0.5% (1 in 200) chance of a CVS causing a miscarriage.
Amniocentesis (amnio)
Usually 16 – 22 weeks (but can be performed later).
If your Combined, Quadruple or NIPT gives a higher-chance result you will be offered an amnio. This will tell you for certain whether or not your baby has Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. It might also be offered if anomalies are seen on a scan
Depending on the tests done on the sample taken by the amnio, other chromosomal or genetic conditions can be diagnosed. There is a 0.5% (1 in 200) chance of an amnio causing a miscarriage.
Detailed fetal anomaly ultrasound scan
18 – 20 weeks and 6 days
At this scan the sonographer will check the baby is developing as expected and check for major fetal anomalies.
Fetal growth scans
28 weeks and later
This scan checks the baby is growing as expected. This is usually only offered to women when there is a concern that the baby might be significantly small.