Prenatal genetic and genomic testing
Prenatal care, also known as ‘antenatal’ or ‘maternity’ care, is the care mothers receive from health professionals during their pregnancy. There are two main categories of genomic and genetic
prenatal testing provided by the NHS:
- Screening tests — tests which look for indicators that a baby may be affected by certain genetic conditions.
- Diagnostic tests — tests which confirm whether or not a baby is affected by a condition.
The goal of prenatal testing is to anticipate potential health problems throughout the course of a pregnancy, and to provide information so that prospective parents can make informed choices. Testing is also routinely performed when a baby is born. Newborn tests are recommended but you can decline if you wish. Prenatal tests are always optional.
Types of prenatal screening tests that may be available to you
Screening for inherited genetic conditions: sickle cell disease and thalassaemia
Sickle cell disease (SCD) and thalassaemia are inherited blood disorders. If you are a genetic carrier of SCD or thalassaemia, you can pass these conditions on to your baby. All pregnant women in England are offered a blood test to find out if they carry a gene for thalassaemia, and those at high risk of being a sickle cell carrier are also offered a test for SCD.
Screening for Down’s, Edward’s, and Patau’s syndromes
- Traditional Screening: All pregnant women in England are also offered a screening blood test for indicators of genetic conditions such as Down’s, Edwards’ or Patau’s syndromes in their child. Test results may be combined with ultrasound measurements and other information, such as a mother’s age, to get a more accurate estimate of the chances that a baby has one of these conditions.
- Non-invasive prenatal screening test (NIPT): A non-invasive prenatal test (NIPT) involves taking a sample of blood from the pregnant mother and examining small fragments of DNA – known as ‘cell free DNA’– floating in the sample. While most of these fragments will be from the mother, a proportion will come from the placenta, and will therefore carry the DNA of the child. NIPT can be conducted to screen for Down’s, Edwards’, and Patau’s syndromes as well as a number of other conditions.
Types of prenatal diagnostic tests that may be offered to you – depending on your circumstances
Invasive diagnostic tests
Chorionic villus sampling and amniocentesis are tests that may be offered during a pregnancy if results of a screening test, or factors such as maternal age or family history indicate that a baby is at risk of a genetic condition.
Both of these tests involve collecting cells from inside the womb (uterus) and are therefore considered ‘invasive’: Chorionic villus sampling (CVS) is performed by taking a small sample of placental tissue (chorionic villi). Amniocentesis involves removing and testing a small sample of cells from the amniotic fluid – the fluid that surrounds the baby in the uterus.
Non-invasive prenatal diagnosis (NIPD) test
Similar to NIPT, a non-invasive prenatal diagnostic (NIPD) test analyses a baby’s DNA from a maternal blood sample. An NIPD test can be used to confirm or rule out a specific condition and may be offered as an alternative to CVS or amniocentesis.
Genetic testing in IVF
A pre-implantation genetic diagnosis (PGD) test is a genomic examination that may be performed during IVF treatment. PGD can be offered when one or both genetic parents have, or are carriers of, a known genetic condition. Testing is performed on embryos created through IVF to determine whether they are at risk of inheriting the condition. The use of PGD enables couples at risk of passing on an inherited condition to decrease the risk of having an affected child.
In the UK, the ‘blood spot’, or ‘heel prick test’, is routinely performed on newborns within the first five days of life. This is a simple blood test.
The test looks for signs of nine rare but serious genetic conditions, including: cystic fibrosis, sickle cell disease, congenital hypothyroidism (this condition is always genetic), phenylketonuria (PKU), medium-chain acyl-CoA dehydrogenase deficiency (MCADD), maple syrup urine disease (MSUD), isovaleric acidaemia (IVA), glutaric aciduria type 1 (GA1), and homocystinuria (HCU).
Early diagnosis identifies babies at risk of developing, or living with a condition, sometimes before they develop symptoms. This means early treatment, leading to better outcomes for the children.