Everyone is at a risk of having a child with a genetic disease, even if they have no family history or symptoms of disease. Carrier screening is a genetic screening for couples and individuals of all ethnic backgrounds who are planning a pregnancy or are early in pregnancy.
Most babies are born healthy; however there is always a risk that something can go wrong. The risk will be greater for some couples than others, depending on age, lifestyle issues, medical history and blood relations to each other (consanguinity).
While couples are generally advised to undergo genetic testing, the decision to do so is ultimately up to them. It’s a good idea to think about why they want to be tested and the consequences for them and their family if they learn that their baby does have a genetic disorder.
Such a test will look for disease-causing changes, called mutations, in a couple’s genes that could cause a genetic disease if inherited by their offspring. The risk of having a child affected with a genetic disease is greater if the couple shares blood relations for example, if they are related.
The information from the carrier screen test can help couples make decisions about their reproductive options and their child’s medical care that may be required.
The carrier screen would cover hundreds of genetic diseases including, but not limited to, Alpha and Beta Thalassemia, Sickle-cell anemia, Spinal Muscular Dystrophy, G6PD and so forth. In fact, many of the diseases included can shorten life expectancy and/ or cause physical/cognitive impairment.
The world of genetic testing is complicated. Genetic counselors help couples understand the complex genetic information, discuss the implications of such testing for the couple and their family, organize the testing, provide in-depth explanations of the results, and guide and support the couple to make informed decisions.
Types of Tests
There are two kinds of tests that can be done in pregnancy:
1. Screening Tests: These can tell you if you are at a risk of having a baby with birth defects. These tests will not give you definite information about the fetus.
These include a combination of blood tests and ultrasound examination and are part of the routine pregnancy check-ups.
2. Diagnostic Tests: These can tell you if the fetus has a defect. These include:
- Chorionic Villus Sampling (CVS) (at 11 to 12 weeks) – In this test a small sample is taken from the placenta. The sample from the placenta can be used for genetic testing. One woman in one hundred (one percent) could have a miscarriage as a result of this test.
- Amniocentesis (at 15 to 18 weeks) – A sample of the amniotic fluid that surrounds the baby is collected and can be used for genetic testing. Amniocentesis has a one in two hundred risk of causing a miscarriage.
- Ultrasound scans (at 18 to 20 weeks) – This second trimester scan is used to identify physical and structural abnormalities including Spina Biﬁda, heart and limb defects.
- Non-Invasive Prenatal Diagnosis (at 10 to 24 weeks) – Noninvasive prenatal testing is a relatively new, and sophisticated blood test that examines fetal DNA from the mother’s blood to determine whether the fetus is at risk of Down Syndrome, extra sequences of chromosome 13 (trisomy 13), extra sequences of chromosome 18 (trisomy 18) or a sex chromosome abnormality, such as Turner’s syndrome. The testing can also be used to determine a fetus’ sex and rhesus (Rh) blood type.
If a couple is found to be carrying a disease-causing mutation, their reproductive options include:
• Screening embryos created by in-vitro fertilization (IVF) before pregnancy
• Continuing naturally with family planning and pregnancy
• Testing the pregnancy via Chorionic Villus Sampling (CVS) of Amniocentesis
• Adopting a child