As our understanding of genetic disorders and the technology necessary to detect them early progresses, the care offered to pregnant women is also changing. Today women undergo much more testing during pregnancy than ever before. This commonly includes non-invasive prenatal testing, which only requires a blood sample from the mother and informs parents of the likelihood that their child could be born with certain genetic disorders.
If you have received an inconclusive or positive result from an initial prenatal blood test, you may be scared and confused. It’s important to remember that a prenatal blood test does not indicate a certainty. Your doctor will likely recommend additional tests to confirm and diagnose your unborn child’s condition. Two of the most commonly recommended prenatal diagnostic tests are amniocentesis and chorionic villus sampling (CVS). What is the difference between the two?
Amniocentesis is a prenatal diagnostic test that is usually performed between the 15th and 20th weeks of pregnancy. This procedure involves using an ultrasound to guide a thin, hollow needle through the abdomen of the mother and into the amniotic sac. The needle will then remove just enough amniotic fluid necessary to test for abnormalities.
Discomfort during and after amniocentesis is minimal. Some women elect for a local anesthetic, but many do not. After the procedure, you may experience very mild pains that can be treated with over-the-counter pain medication, as recommended by your doctor. Plan to rest and avoid any strenuous physical activity for at least 48 hours after the test. If you experience any severe abdominal pain, bleeding, fever or other serious symptoms following the procedure, you should alert your doctor as soon as possible. There is a very slight risk of miscarriage associated with an amniocentesis (less than 1%), but the results can have a significant impact on planning for future healthcare for your baby if they have a diagnosis requiring special medical attention.
The results of amniocentesis should be available within four weeks of the procedure. This test is usually around 99.4% accurate in detecting chromosomal abnormalities in utero. You will likely be required to meet with a genetic counselor to go over the results. They will be able to give you a better idea of how likely it is that your child will be born with a particular disorder, how the results will impact your care during the remainder of the pregnancy, and if the result is positive, what you can do to prepare for the future medical care of your baby.
Chorionic Villus Sampling (CVS)
Chorionic villus sampling is a test that is usually performed between the 10th and 14th weeks of pregnancy. This procedure involves taking cells from a pregnant woman’s placenta (chorionic villus) to test for potential genetic abnormalities in the fetus. There are two ways that this sample can be taken: transcervically (through the cervix), or transabdominally (through the vagina). Before the procedure, the mother will undergo an ultrasound to verify the age of the fetus and the positioning of the placenta for the procedure. During the procedure, a hollow needle will be inserted into the uterus (via the abdomen or through the cervix, via the vagina) to remove chorionic villus cells from the placenta to send for testing.
Your doctor may use a local anesthetic to numb the area prior to sampling. Following the procedure, you may experience light vaginal bleeding and cramping, but any other more serious side effects should be reported immediately to your doctor. Chorionic villus sampling has a slightly higher risk of miscarriage, but it’s still quite low (around 0.22% chance of miscarriage). The results of the test should be available within a week of the study, and are generally 98-99% accurate. There is a possibility that you receive a false positive or need additional testing after CVS. Your doctor or genetic counselor will be able to better advise what course of action to take following testing.
Speak with Your Doctor
If you have additional questions about prenatal testing, or are looking for guidance after receiving your results, speak with your doctor or make an appointment with a genetic counselor. They will be able to answer your questions, make recommendations, and help you to coordinate the necessary future care for your child.