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The sample will be used to study the DNA, chromosomes, and enzymes of the fetus. It is often performed during the first trimester or 10 to 13th week of pregnancy. However, this procedure has also been prescribed to as early as eight week of pregnancy to mothers at special circumstances.
This procedure involves the removal of a small piece of placenta tissue, also called chorionic villi, from the uterus for laboratory tests. Chorionic villus sampling uses an ultrasound to pick the safest method and serves as guide during the sampling.
First, the abdominal ultrasound is performed in determining the position of the uterus, the size of the gestational sac, and the position of the placenta within the uterus. After which, the vulva, vagina, cervix, and abdomen are disinfected using antiseptic such as Betadine.
There are two ways to perform this procedure: transcervical or transabdominal method. Both methods are equally safe when done by experienced doctors. However, studies show that chances for miscarriage are potentially high when done through the cervix.
Using an ultrasound in guiding the process, the transcervical procedure entails inserting of a thin plastic tube through the vagina and cervix until it reaches the placenta. Then, the doctor will remove a sufficient amount of chorionic villus tissue for sampling.
On the other hand, the transabdominal procedure is done by inserting a needle which passes through the abdomen, uterus, and into the placenta. Ultrasound is also used in this process for guidance. The same amount of chorionic villus tissue is removed for sampling.
After removing the sample, this is placed on a dish and is delivered to the laboratory for testing. The test results may take about one to two weeks. Abnormal results may mean more than 200 disorders including Down syndrome, hemoglobinopathies, and Tay-Sachs disease to name a few.
Aside from prenatal diagnosis, Chorionic villus sampling is a procedure to identify chromosomal or genetic disorders in the fetus. In some cases such as the pregnant woman is 35 years of age and above, there is an abnormal first trimester screen results, or there is an increased nuchal translucency, this procedure is also recommended. However, chorionic villus sampling cannot detect neural tube defects and Rh incompatibility.
The risks of chorionic villus sampling are higher than amniocentesis. There are higher chances for miscarriage, infection, and amniotic fluid leakage. The amniotic fluid leakage can also lead to low amniotic fluid level – a condition known as oligohydramnios. If this condition is not treated, the child can develop a hypoplastic lungs or underdeveloped lungs.
Other risks include possible complications such as bleeding, infection, Rh incompatibility in the mother, and rupture of membranes. Symptoms of complications include fever and excessive bleeding and vaginal discharge.
In addition, it may also cause limb problems in the fetus although this is rather low when the procedure is performed after 10 weeks gestational age.
