Chorionic villus sampling (CVS), also known as chorionic villus biopsy, is a prenatal examination involving the extraction of placental tissue to identify chromosomal abnormalities and specific genetic issues. The placenta, situated in the uterus, serves to deliver blood and nutrients from the mother to the fetus.
Chorionic villi, resembling finger-like projections of placental tissue, carry the same genetic makeup as the fetus. Depending on family history and laboratory capabilities, testing might extend to other genetic disorders during the procedure.
Typically performed between the 10th and 12th weeks of pregnancy, CVS differs from amniocentesis, another prenatal test, in that it does not provide insights into neural tube defects like spina bifida. Consequently, women undergoing CVS require a subsequent blood test between the 16th and 18th weeks of pregnancy to screen for such defects.
Two primary methods of CVS exist:
- Transcervical: This technique involves inserting a catheter through the cervix into the placenta to collect the tissue sample.
- Transabdominal: Here, a needle is inserted through the abdomen and uterus into the placenta to obtain the tissue sample.
Amniocentesis is another relevant procedure used to diagnose genetic and chromosomal defects.
Anatomy of the fetus in utero
Amniotic sac: A delicate sac that envelops the fetus throughout pregnancy. Filled with amniotic fluid produced by the fetus, it includes the amnion, a membrane shielding the fetal side of the placenta, safeguarding against harm and maintaining fetal temperature.
Anus: The opening situated at the end of the anal canal.
Cervix: The lower segment of the uterus extending into the vagina. Composed mainly of fibrous tissue and muscle, it possesses a circular shape.
Fetus: The term used to describe an unborn baby from the eighth week following fertilization until birth.
Placenta: An organ resembling a flat cake that develops solely during pregnancy. It facilitates metabolic exchange between the fetus and the mother, allowing the fetus to receive oxygen, nutrients, and other essential substances while eliminating carbon dioxide and waste products.
Umbilical cord: A cord resembling a rope that links the fetus to the placenta. It comprises two arteries and a vein, transporting oxygen and nutrients to the fetus and removing waste products from it.
Uterine wall: The lining of the uterus.
Uterus (womb): A hollow, pear-shaped organ situated in the lower abdomen of women, positioned between the bladder and the rectum. It sheds its lining monthly during menstruation and serves as the site for the implantation of a fertilized egg (ovum) and subsequent fetal development.
Vagina: An integral part of the female reproductive system located behind the bladder and in front of the rectum. It forms a canal stretching from the uterus to the vulva.
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Reasons for the procedure
Chorionic villus sampling is a procedure commonly employed for genetic and chromosomal testing during the initial stages of pregnancy. Here are several reasons why a woman might opt for CVS:
- A previous child affected by a genetic disease, or a family history indicating genetic disorders, chromosomal abnormalities, or metabolic disorders.
- Maternal age exceeding 35 years by the expected date of delivery.
- Elevated risk of a sex-linked genetic ailment.
- Previous ultrasound results showing dubious or abnormal findings.
- Abnormal outcomes from cell-free DNA testing.
Additionally, there could be other factors prompting your doctor to suggest chorionic villus sampling.
Pros and Cons of Chorionic villus sampling (CVS)
Pros:
- Early Detection
- Accurate Results
- Personalized Care
- Peace of Mind
Cons:
- Risk of Complications
- Limited Information
- Invasive Procedure
Differences Between Chorionic villus sampling (CVS) and Vienva
Chorionic Villus Sampling (CVS):
CVS is a prenatal diagnostic procedure used to detect chromosomal abnormalities and genetic disorders in the fetus during early pregnancy, typically between 10 to 13 weeks gestation.
Vienva:
Vienva is a brand of combination birth control pill that contains two hormones, estrogen, and progestin, designed to prevent pregnancy by inhibiting ovulation, thickening cervical mucus to prevent sperm from reaching the egg, and thinning the uterine lining to prevent implantation.
Alternative to Chorionic villus sampling (CVS)
Amniocentesis:
Amniocentesis is a prenatal diagnostic procedure performed typically between 15 to 20 weeks of pregnancy. During amniocentesis, a small amount of amniotic fluid is extracted from the amniotic sac surrounding the fetus. This fluid contains fetal cells that can be analyzed for chromosomal abnormalities and genetic disorders. Amniocentesis carries a similar risk of complications as CVS but is often preferred for its lower risk of miscarriage.
Risks of the procedure
Like any invasive procedure, chorionic villus sampling (CVS) carries potential complications, including:
- Cramping, bleeding, or amniotic fluid leakage (rupture of membranes).
- Risk of infection.
- Miscarriage.
- Onset of preterm labor.
- Rare occurrence of limb defects in infants, particularly in CVS procedures conducted before the 9th week of pregnancy.
- Individuals allergic to medications or latex should inform their doctor beforehand.
- Women carrying twins or multiples require sampling from each placenta to assess each baby's condition.
Other risks may vary depending on individual medical circumstances. It is important to discuss any concerns with your doctor prior to the procedure.
Certain factors or conditions may impede CVS, such as:
- Pregnancy occurring earlier than seven weeks or later than 13 weeks.
- Baby's position, placental location, amount of amniotic fluid, or maternal anatomy.
- Presence of vaginal or cervical infections.
- Inadequate samples for testing or samples containing maternal tissue.
Before the procedure
Your doctor will guide you through the procedure, allowing you to address any questions you may have.
Before undergoing chorionic villus sampling (CVS), you'll be requested to sign a consent form, granting permission for the procedure. Ensure you review the form carefully and seek clarification on any unclear aspects.
Typically, there are no specific dietary or activity restrictions preceding CVS.
Inform your doctor about any sensitivities or allergies to medications, latex, iodine, tape, and anesthetic agents (both local and general).
Disclose all medications, including prescribed, over-the-counter, and herbal supplements that you're currently taking.
Inform your doctor about any history of bleeding disorders or if you're using anticoagulant (blood-thinning) medications, aspirin, or any other drugs affecting blood clotting. It may be necessary to discontinue these medications before the procedure.
If you're Rh negative, inform your doctor. During CVS, mixing of blood cells from the mother and fetus might occur, potentially leading to Rh sensitization and breakdown of fetal red blood cells. In most cases, prenatal blood tests would have already determined your Rh factor. You may be required to provide these lab results before the procedure.
Depending on the position of the uterus and placenta, you may or may not be advised to have a full bladder just before the procedure. A full or empty bladder may aid in positioning the uterus optimally for the procedure.
Your doctor may recommend additional specific preparations based on your medical condition.
During the procedure
A chorionic villus sampling (CVS) procedure can typically be conducted on an outpatient basis or as part of a hospital stay, depending on your condition and your doctor's preferences.
Here's a general outline of what to expect during a CVS procedure:
- You'll be asked to disrobe completely or from the waist down and wear a hospital gown.
- You'll lie down on an examination table and position your hands behind your head.
- Your vital signs, including blood pressure, heart rate, and breathing rate, will be monitored.
- An ultrasound will be performed to assess the fetal heart rate and determine the position of the placenta, fetus, and umbilical cord.
- Depending on the placental location, the CVS procedure will be conducted either through your cervix (transcervical) or through your abdominal wall (transabdominal).
For a transcervical CVS procedure:
- The doctor will insert a speculum into your vagina to visualize your cervix.
- Your vagina and cervix will be cleansed using an antiseptic solution.
- With the guidance of ultrasound, a thin tube will be carefully directed through your cervix to reach the chorionic villi.
- Cells will be gently suctioned through the tube into a syringe. You might experience a twinge or mild cramping during this process. Multiple samples may be required to collect enough tissue for testing.
- Finally, the tube will be removed.
For a transabdominal CVS procedure:
For an abdominal CVS procedure, the following steps are typically involved:
- Your abdomen will be cleansed with an antiseptic solution. You'll be instructed not to touch the sterile area on your abdomen during the procedure.
- The doctor may administer a local anesthetic to numb the skin. If a local anesthetic is used, you'll feel a needle stick during the injection, which might cause a brief stinging sensation.
- Ultrasound will be utilized to guide a long, thin, hollow needle through your abdomen, into the uterus, and ultimately to the placenta. This part of the procedure may cause slight discomfort, and you may experience cramping as the needle enters the uterus.
- Cells will be gently suctioned into a syringe. Multiple samples may be necessary to collect enough tissue for testing.
- Subsequently, the needle will be withdrawn, and an adhesive bandage will be applied over the site where the needle was inserted into the abdomen.