VMBO Year 3 · Reproduction and sexuality · Section 2.8

Genetic testing

What is genetic testing?

Genetic testing can investigate whether someone has an inherited condition or is a carrier. A carrier of a recessive condition has one disease-associated allele and usually does not have the condition, but can pass that allele to a child. The child's chance of having the condition also depends on the other parent's genetic information.

If an inherited condition runs in a family, or following repeated miscarriages, genetic counselling can help clarify possible causes and risks. A specialist may examine a family history and arrange chromosome or DNA tests. This helps people make informed decisions about pregnancy.

Testing before birth

Prenatal testing investigates a developing baby before birth. Screening estimates the chance of particular conditions; diagnostic testing can establish whether specific conditions are present. No test detects every condition. People can choose whether to undergo testing after discussing its possibilities and limitations.

Ultrasound

An ultrasound scan uses high-frequency sound waves to produce an image of the developing baby. It can assess growth and identify some structural differences. Medical ultrasound does not use ionising radiation and has no known harmful effects when used appropriately, but it cannot rule out all conditions.

NIPT

The non-invasive prenatal test, or NIPT, is a blood test on the pregnant person. It examines small fragments of DNA from the placenta circulating in the blood; these usually represent the baby's chromosome pattern. In the Netherlands it can be performed from 10 weeks of pregnancy. An abnormal screening result can be followed by diagnostic testing, because NIPT alone does not give a definite diagnosis.

Chorionic villus sampling

Chorionic villus sampling, or CVS, takes a small sample of placental tissue for chromosome or genetic testing. It is offered from approximately 11 weeks. The procedure carries a small additional risk of miscarriage.

Amniocentesis

During amniocentesis, a needle is used to collect a small amount of amniotic fluid containing foetal cells. These can be examined for chromosome differences or particular genetic conditions. It is generally performed from approximately 15 weeks and also carries a small additional miscarriage risk.

The choice of tests depends on the situation, the stage of pregnancy and the information the parents want. Pregnancy weeks here are counted from the last menstrual period.