Prenatal diagnostic tests are performed during pregnancy to learn if a baby has a genetic condition, such as Duchenne muscular dystrophy (DMD). Expectant parents with natural pregnancies and those who used assistive reproductive technologies like in-vitro fertilization (IVF) might both pursue this type of testing, since the genetic testing performed earlier on in IVF isn’t always accurate.
When is prenatal testing for DMD offered?
All pregnant women receive standard prenatal screening that uses blood tests to check for several genetic conditions and birth defects, but this standard prenatal screening protocol doesn’t test for Duchenne. As DMD is a rare disorder and is most often inherited, prenatal testing for the disease is generally only performed when there is a risk of the disease occurring.
Prenatal testing for DMD is offered when there is a family history of DMD, a previous pregnancy was affected by DMD or the mother is a known carrier. DMD is caused by a mutation on the dystrophin gene, found on the X chromosome, meaning that while men are the most often affected, women are carriers.
How is prenatal testing for DMD performed?
Prenatal testing is done using fetal DNA. To obtain fetal DNA, there are two main options: chorionic villus sampling (CVS) and amniocentesis.
CVS can be performed at 10 to 13 weeks of pregnancy and involves inserting a long thin needle into the pregnant mother’s abdomen or cervix. Ultrasound imaging guides the needle as it extracts tissue from the placenta, which will have the same genetic makeup as the fetus.
Amniocentesis can be performed at 15 to 20 weeks of pregnancy. It also involves inserting a long thin needle into the abdomen, but instead of taking a tissue sample this test extracts amniotic fluid from the uterus.
Both methods are highly accurate, but a small risk of miscarriage exists: for CVS the risk is one in 450 cases, and for amniocentesis it is less than one in 900.
After the samples are collected, they are then analyzed using advanced genetic testing, and an accurate diagnosis is made. If the mutation is identified in a male fetus, DMD is confirmed; if it is identified in a female fetus, she will be a carrier, and in most cases unaffected by the condition.
A genetic counselor will play an important role in accompanying parents when a DMD diagnosis is made, helping to explain the results and the next steps.
Are there other testing options?
Noninvasive prenatal testing involves analyzing pieces of fetal DNA collected during a maternal blood test, and can be performed from 10 weeks into pregnancy. This testing method can indicate the sex of a fetus. While it can test for chromosomal disorders like Down syndrome, it is not generally used to screen for DMD, though some early research indicates it may have the potential to help idenifty the disease.
However, this specialized screening method is not universally available, and results need to be confirmed by more invasive diagnostic testing.
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