1. Pregnancy
  2. Pregnancy health
  3. Prenatal testing

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Chorionic Villus Sampling: CVS vs. Amniocentesis

A prenatal test combining an ultrasound with placenta tissue sampling, chorionic villus sampling (CVS) detects fetal abnormalities to safeguard the health of mother and child. Next, Flo summarizes the advantages and disadvantages of CVS vs. amniocentesis.

Exactly what is chorionic villus sampling? Also called chorionic villus biopsy, it’s a prenatal screening in which a placenta tissue sample is used to search for chromosomal abnormalities and other genetic issues. Typically, the CVS procedure is conducted between the 10th and 12th weeks of pregnancy.

CVS may be broken down into two categories: 

  • Transabdominal

The doctor inserts a needle through the abdomen and into the womb to obtain a placenta tissue sample.

  • Transcervical

Alternatively, the doctor performs CVS by inserting a catheter into the cervix to obtain a placenta tissue sample.

You and your doctor might opt for CVS for one of the following reasons:

  • There’s a family history (in current or past generations) of chromosomal abnormalities, metabolic disorders, or genetic diseases.
  • You’ll be 35 years or older by the baby’s due date.
  • You could carry a sex-linked genetic disease.
  • Previous ultrasound examinations produced irregular or inconclusive results.
  • A cell-free DNA test was abnormal.

The potential negative side effects of chorionic villus sampling include:

  • Bleeding, cramping, or leakage of amniotic fluid
  • Miscarriage
  • Infection
  • Preterm labor
  • Infant limb defects (especially if the CVS procedure is done before the ninth week)

Be sure to inform your doctor of any drug allergies or a sensitivity to latex. In the event of a multiple pregnancy, they’ll collect and test tissue from each fetus’ placenta. Note that additional safety measures might be required depending on personal medical history, and it’s wise to share all concerns prior to the CVS procedure.

Certain factors have been known to interfere with CVS, including:

  • Scheduling the procedure before week 7 or after week 13
  • Positioning of the fetus and placenta, your anatomy, and the amount of amniotic fluid present
  • Cervical or vaginal infections
  • Insufficiently-sized testing samples or those containing maternal tissue

Chorionic villi are small finger-like projections in the placenta and their genetic material is identical to that of the fetus. Note that chorionic villi sampling is either performed in an outpatient or hospital setting. Protocols vary depending on your condition and the health care provider. Typically, the steps involved in CVS are as follows:

  • You’ll be asked to undress (either completely or from the waist down) and put on a hospital gown.
  • They’ll have you lie down on the examination table and place both hands behind your head.
  • Vital signs such as breathing, heart rate, and blood pressure will all be checked.
  • You’ll undergo an ultrasound to examine fetal heart rate and positioning, as well as the condition of the umbilical cord and placenta.
  • Based on placenta location, a CVS procedure is done via the cervix or abdominal wall.

A transcervical CVS includes:

  • Inserting a speculum into your vaginal cavity
  • Cleaning your cervix and vagina with antiseptic
  • Guiding a thin tube into the cervix using ultrasound technology
  • Gently suctioning chorionic villi cells into a syringe, then removing the tube

A transabdominal CVS includes:

  • Cleaning your abdomen with antiseptic
  • Injecting a local anesthetic to numb the skin
  • Guiding a thin, long, hollow needle into the abdomen, womb, and placenta using ultrasound technology
  • Gently suctioning chorionic villi cells into a syringe
  • Removing the needle and applying a bandage over the insertion site

Next, let’s review the basics of what is probably the most well-known prenatal test: amniocentesis.

During an amniocentesis, a small sample of amniotic fluid (which surrounds the fetus while in utero) is obtained. Your baby produces this clear, pale yellow fluid to protect itself from injury and regulate body temperature.

Apart from various enzymes, hormones, and proteins, amniotic fluid also contains fetal cells with genetic information. Your doctor can use it to diagnose open neural tube defects (ONTDs), such as spina bifida and chromosomal disorders.

When carried out in the later stages of pregnancy, an amniocentesis could detect infections and determine lung maturity (in the event of an early delivery).

If you have an increased likelihood of developing chromosomal abnormalities, your doctor will offer to conduct an amniocentesis between weeks 15 and 20. 

An amniocentesis for chromosome and genetic testing is recommended in the second trimester under the following circumstances:

  • There’s a family history (in current or past generations) of chromosomal abnormalities, metabolic disorders, or genetic diseases.
  • You’re at risk for ONTDs like spina bifida.
  • You’ll be 35 years or older by the baby’s due date.
  • Screening tests revealed unusual levels of maternal serum alpha-fetoprotein (MSAFP).
  • You could carry a sex-linked genetic disease.

Additionally, amniocentesis may be utilized in the third trimester to assess:

  • Uterine infections
  • Fetal lung maturity (if premature birth is a possibility)
  • Rh disease

The potential negative side effects of an amniocentesis procedure include:

  • Cramping
  • Infection
  • Miscarriage
  • Bleeding or leakage of amniotic fluid (either from the vagina or puncture site)
  • Preterm labor

Certain factors have been known to interfere with the process of amniocentesis, including: 

  • Scheduling the procedure prior to the 14th week of pregnancy
  • Positioning of the fetus and placenta, your anatomy, and the amount of amniotic fluid present

Typically, the steps involved in an amniocentesis are as follows:

  • You’ll be asked to undress (either completely or from the waist down) and put on a hospital gown.
  • They’ll have you lie down on the examination table and place both hands behind your head.
  • Vital signs such as breathing, heart rate, and blood pressure will all be checked.
  • You’ll undergo an ultrasound to examine fetal heart rate and positioning of the fetus, umbilical cord, and placenta to locate an amniotic fluid pocket.
  • The abdomen is cleaned with antiseptic and a local anesthetic will likely be injected.
  • Guided by ultrasound technology, a long, thin, hollow needle is inserted into the abdomen, womb, and amniotic sac.
  • Less than an ounce of amniotic fluid is removed with a syringe, then placed in a special light-protected container and sent for lab analysis.
  • The needle is removed and a bandage is applied over the insertion site.
  • Vital signs and fetal heart rate are checked once more. 
  • If your blood happens to be Rh-negative, you may receive Rhogam. It’s a product designed to prevent a reaction between your Rh-negative antibodies and the baby’s Rh-positive cells.

The primary advantage of undergoing a CVS procedure is that genetic abnormalities can be discovered in the first trimester of pregnancy. While chorionic villus sampling is a very precise detection tool, there are certain problems it cannot pick up that amniocentesis can, such as:

  • Birth defects
  • Neural tube defects (in the fetus’ brain or spinal column)
  • Rh incompatibility (i.e., when an Rh-negative mother carries an Rh-positive fetus)

Amniocentesis could be the best prenatal test option if you:

  • Or your partner were born with a neural tube defect
  • Have already given birth to a baby with a neural tube defect
  • Received other abnormal test results during pregnancy, including early prenatal blood screenings

Only you together with your doctor may decide whether you need prenatal screening. With pregnancy comes an almost overwhelming mixture of excitement and worry. Although the majority of children are born in excellent health, prenatal tests like CVS and amniocentesis can offer added peace of mind. 

Ultimately, however, prenatal screening is optional and based on you and your partner’s wishes. Consider discussing the pros and cons of chorionic villus sampling and amniocentesis with a doctor or genetic counselor to better understand what’s involved.

https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/chorionic-villus-sampling-cvs

https://www.stanfordchildrens.org/en/topic/default?id=amniocentesis-procedure-92-P07762

https://familydoctor.org/prenatal-diagnosis-amniocentesis-and-cvs/

https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-testing/art-20045177

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