A couple planning to become parents should consider prenatal (before birth) testing if one (or both) has tested positive for the Huntington’s disease (HD) gene, or has a family history of HD.

In prenatal testing, a DNA sample is taken and tested after pregnancy has begun and the pregnancy is usually only continued if the HD genetic test is negative.

Deciding whether to test an unborn baby is a difficult and often emotional decision; it requires careful consideration, preferably before becoming pregnant. Once a woman is pregnant, there isn’t a great deal of time for the decision-making process, as the testing must be carried out early in the pregnancy. It’s therefore important to consult your doctor as soon as you realise you’re pregnant.

Prior to prenatal testing, the couple should have made the decision that they’ll terminate the pregnancy if the foetus is found to be carrying the gene. This is because undergoing a prenatal test – assuming the pregnancy isn’t terminated – takes away the child’s right to choose whether to have the genetic test later in life. Many adults at risk for HD choose not to have the test before they start to develop symptoms.

Prenatal testing procedure

To test the foetus, medical procedures called chorionic villus sampling (CVS) or amniocentesis are performed.

CVS involves collecting a small sample of tissue from the chorionic villus (part of the developing placenta), which has the same genes as the foetus. CVS is a quick outpatient procedure. To collect the sample, a fine needle, guided by an ultrasound scanner, is passed either through the vagina and cervix or through the abdomen. The cells are tested in the laboratory for the presence of the HD gene mutation.

CVS is usually carried out between 10 and 12 weeks into a pregnancy. At this early stage, a pregnancy can still be kept from family and friends, should the parents want it. It’s also best, if termination of the pregnancy is required, for this to be performed at an early stage.

Prenatal testing can also be performed by amniocentesis. In this case, a fine needle is passed into the mother’s abdomen to take a small sample of amniotic fluid, which surrounds the developing foetus and contains some foetal skin cells. The sample is then sent to a laboratory to be studied for the presence of the HD mutation in the foetal cells. This test is done at around 14-18 weeks into the pregnancy.

Both CVS and amniocentesis are quick outpatient procedures and considered very safe. The main potential complication related to these tests is miscarriage, but the risk of this is very low: about 1% (1 in 100 pregnancies) with CVS, and about 0.5% (1 in 200 pregnancies) in the case of amniocentesis.

Sources:
– Daley, A. Huntington’s Disease Society of America. Family Planning and Huntington’s Disease: Considering Options and Making Decisions.
– National Genome Research Institute. National Institutes of Health. Is there a test for Huntington’s disease?

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