Chorionic Villi Sampling - Indications and Benefits

Introduction:

Chorionic villi sampling is a prenatal diagnostic that involves obtaining a sample of placental tissue from the uterus and tested for genetic or chromosomal abnormalities. It is done between 10 to 12 weeks of pregnancy.

What Are Chorionic Villi?

Chorionic villi are finger-like projections in the outer layer of the embryo (chorion) and contain a network of blood vessels. These structures serve as a means of exchanging nutrients, oxygen, and waste products between the developing fetus and the mother's bloodstream. Chorionic villi are covered in a layer of cells that produce hormones that are necessary for maintaining pregnancy, including human chorionic gonadotropin (hCG) and progesterone. These hormones play critical roles in supporting the growth and development of the embryo and fetus. During prenatal testing, a small sample of chorionic villi will be collected and analyzed for genetic abnormalities or other conditions that may affect the health of the developing fetus.

What Are the Indications for Chorionic Villi Sampling?

Chorionic villi sampling is done in the first trimester of pregnancy and is recommended for people with an increased risk of developing genetic disorders. Down syndrome, hemophilia, sickle cell anemia, spinal muscular atrophy, mosaicism, and cystic fibrosis are some of the disorders that can be detected by chorionic villi sampling.

Some indications for the procedure include the following:

• Women above the age of 35 years (advanced maternal age) are at higher risk of having babies with genetic disorders.

• Women who have a previous child with genetic or chromosomal abnormalities are at increased risk of having the next child with abnormalities.

• Parents with a history of a genetic disease.

• Women with a family history of disorders like sickle cell anemia or cystic fibrosis are recommended for chorionic villi sampling to determine if the fetus is affected.

• Abnormal results from other prenatal screening tests.

• If there are concerns about the health of the developing fetus, such as abnormal ultrasound findings, Chorionic villi sampling may be recommended to diagnose or rule out specific conditions.

How Is Chorionic Villi Sampling Done?

Chorionic villus sampling (CVS) is performed between the 10th and 13th week of pregnancy.

Before the procedure, a thorough medical history and physical examination will be made to evaluate the patient.

Chorionic villi sampling can be performed either through the abdomen or the cervix.

1. Transabdominal CVS:

This is the most common method of CVS. An ultrasound-guided needle is inserted through the abdomen into the uterus. It is then inserted into the chorionic villi of the placenta, and a small sample of tissue is suctioned into the needle.

2. Transcervical CVS:

In this method, a speculum is inserted into the vagina to expose the cervix. A thin tube is then passed through the cervix and into the uterus, where a small sample of chorionic villi is suctioned into the tube.

The collected tissue will be sent to a genetic laboratory for testing. Depending on the results, a genetic counseling session may be scheduled. After the procedure, the fetal heart rate will be monitored. The mother will be asked to avoid strenuous physical activity and exercises.

What Are the Benefits of Chorionic Villi Sampling?

The benefits of chorionic villus sampling (CVS) include:

• Early Diagnosis: CVS is performed between 10 and 13 weeks of pregnancy, which is earlier than other diagnostic tests such as amniocentesis. Early diagnosis can provide more time for parents to prepare for the birth of a child with a genetic or chromosomal abnormality and make informed decisions about their pregnancy.

• Accurate Diagnosis: CVS is a highly accurate diagnostic test, with a reported accuracy rate of over 99 %. This high level of accuracy allows parents to make informed decisions about their pregnancy based on reliable information.

• Reduced Anxiety: For women who are at increased risk of having a baby with a genetic or chromosomal abnormality, the uncertainty about the health of their baby can be a significant source of anxiety. CVS can reduce anxiety by either ruling out the possibility of a problem or providing a definitive diagnosis.

• Opportunity for Early Treatment: In some cases, early diagnosis of a genetic or chromosomal abnormality may allow for early treatment or intervention to improve the outcome for the baby.

What Are the Risks of Chorionic Villi Sampling?

Chorionic villus sampling (CVS) is generally considered a safe procedure, but some potential risks should be considered, including:

• Miscarriage: In some cases, there can be a risk of miscarriage following the procedure.

• Infection: There is a small risk of infection associated with CVS. Symptoms of the infection can include fever, abdominal pain, and vaginal discharge.

• Bleeding: Some women may experience light bleeding and cramping after CVS, which is usually not a cause for concern. However, heavy or persistent bleeding should be reported to a healthcare provider.

• Amniotic Fluid Leak: There is a risk of amniotic fluid leakage from the puncture site after the procedure.

• False-negative Results: While CVS is a highly accurate diagnostic test, there is a small risk of false-negative results.

• Emotional Risks: For some women, undergoing prenatal diagnostic testing can be emotionally stressful, regardless of the results. Women who are considering CVS should discuss their concerns with a healthcare provider or a counselor to reduce their anxiety.

What Is the Difference Between Chorionic Villi Sampling and Amniocentesis?

• Chorionic villi sampling and amniocentesis are prenatal diagnostic procedures. While chorionic villi sampling is done in 10 to 13 weeks, amniocentesis is performed between 15 and 20 weeks.

• Chorionic villi sampling analyzes cells from the chorionic villi, which are cells that originate from the fertilized egg and are, therefore, genetically identical to the fetus. Amniocentesis analyzes cells from the amniotic fluid, which include cells that have been shed by the fetus, as well as cells from the placenta.

• Chorionic villi sampling cannot provide details about neural tube defects. Neural tube defects can be identified by amniocentesis, which is performed in the later weeks of pregnancy.

Conclusion:

Chorionic villi sampling can be a valuable tool in the prenatal diagnosis of genetic disorders and can assist parents in making informed decisions regarding their pregnancy and plan for the future. It is advisable to discuss the procedure, the benefits, and the risk with a medical professional for better outcomes.