Introduction
Prenatal diagnosis refers to the diagnosis made before delivery (childbirth). Prenatal tests allow the doctor to diagnose any health issues in the developing baby. Chorionic villus sampling (CVS) and amniocentesis are prenatal diagnostic tests. These tests help in the prenatal detection of genetic abnormalities. The possibility of a child being born with a genetic condition or any other health issues is higher for some parents.
With the help of chorionic villus sampling (CVS) and amniocentesis, the parents can know about their baby's health before the baby is born. This allows the parents to make better decisions about the baby's medical treatment. Some health issues can be resolved before the baby's birth. Other issues may need immediate treatment following childbirth.
What Is Chorionic Villus Sampling?
The placenta is an organ located inside the uterus that carries nutrients and blood from the mother's body to the developing fetus. The chorionic villi look like small fingers and are made of placental tissue. It contains the same genetic material as that of the developing fetus. A sample of placental tissue is taken during chorionic villus sampling (CVS) to check for chromosomal abnormalities as well as additional genetic problems.
According to the family history and the condition of the mother, testing for genetic abnormalities and illnesses can be done through chorionic villus sampling. Usually, chorionic villus sampling is performed during the 10th to 12th week of pregnancy. Unlike other prenatal tests (pregnancy tests performed to assess the health of the mother and the unborn child), chorionic villus sampling does not provide information about neural tube disorders like spina bifida (a birth defect with an abnormal spinal cord).
As a result, women who undergo chorionic villus sampling also need to undergo a blood test during the 16th to 18th week of pregnancy to screen for any neural tube (tube-shaped structure enclosing the baby's brain and spinal cord) abnormalities. Chorionic villus sampling procedures can be performed in two ways. They are:
- Transcervical - A catheter is inserted through the cervix during the transcervical procedure to remove a sample of placental tissue.
- Transabdominal - The transabdominal procedure involves a needle inserted into the uterus and abdomen to remove a sample of placental tissue.
What Is Amniocentesis?
Amniocentesis is a diagnostic procedure. It is performed during pregnancy to identify whether the baby has a genetic or chromosomal problem. In amniocentesis, a small volume of cells from the amniotic fluid (the fluid around the growing baby in the uterus) is extracted and examined. In most cases, amniocentesis is usually performed between weeks 15 and 20 of pregnancy.
Although amniocentesis can be done early in the pregnancy, this is typically avoided as it may raise the chance of complications. During amniocentesis, an ultrasound image is used as guidance, and a long, thin needle is inserted into the abdominal wall. The baby's amniotic sac (the fluid-filled around the baby) is pierced with a needle, and a small amount of amniotic fluid is taken out for examination. Amniocentesis is usually characterized as uncomfortable rather than painful. Some women report experiencing pressure or having pain similar to menstrual pain when the needle is removed.
Why Is Chorionic Villus Sampling Done?
Chorionic villus sampling is performed during the first trimester of pregnancy for genetic and chromosome testing. A woman may opt to have chorionic villus sampling for a variety of reasons, including:
- If there is a family history of genetic diseases, chromosomal abnormalities, or metabolic disorders, or if she has previously given birth to a child affected by any of these issues.
- If the mother is older than 35 at the time of the pregnancy (older mothers are more likely to have genetic problems).
- If there is a chance of a sex-linked genetic illness.
- If a previous ultrasound revealed suspicious or abnormal results.
- If the results of the cell-free DNA (deoxyribonucleic acid) test were abnormal.
What Are the Risks Associated With Chorionic Villus Sampling and Amniocentesis?
- Chorionic villus sampling carries the same risks as amniocentesis, which include bleeding, infection, rupture of membranes, pregnancy loss, and unpredictable outcomes.
- With the help of ultrasound guidance and improved expertise and practice, the rate of pregnancy loss has decreased.
- The frequency of needle or catheter insertions, the operator's expertise, pregnancies because of assisted reproductive technologies (infertility treatments), and the use of transcervical cannulas are all associated with an increased risk of fetal loss.
- Furthermore, the research has linked the potential risks of chorionic villus sampling to oromandibular hypogenesis (malformation of the face) and limb reduction abnormalities (limb defects). These issues have been linked to early chorionic villus sampling (before 10 weeks of gestation). In this regard, the World Health Organization estimates the risk of limb deformities to be roughly 6 per 10,000, which is similar to the risk in the general population.
- When chorionic villus sampling tests are conducted before 10 weeks, it is important to inform the patient about the outcomes, even though the risk is low.
- Up to 32 percent of women have reported experiencing vaginal spotting (vaginal bleeding), which is more common following transcervical chorionic villus sampling.
- It is reported that the incidence of infection, amniotic fluid leaking, and culture failure following chorionic villus sampling is less than 0.5 percent.
Conclusion
Amniocentesis and chorionic villus sampling are two prenatal diagnostic techniques (used for prenatal genetic testing). These test results will give the patients the option to seek early referral to pediatric subspecialists, counseling for obstetric treatments and recommendations (if the results are abnormal), and earlier and safer methods of terminating their pregnancy. Chorionic villus sampling is a well-established and comparatively risk-free method of performing early diagnostic prenatal genetic testing. With the progress of ultrasound technology and a qualified clinician, complications are rare for chorionic villus sampling.
