Overview of Chorionic Villus Sampling
Chorionic villus sampling is a procedure done between the 10th and 13th weeks of pregnancy to test the placenta for genetic conditions. The main benefit of this test is that it gives results early on in the pregnancy. This early detection allows those expecting to seek advice regarding care during pregnancy and recommendations, get a sooner referral to pediatric specialists, or explore earlier and safer ways to end the pregnancy if the test results are abnormal.
Why do People Need Chorionic Villus Sampling
The American College of Obstetrics and Gynecology suggests that all women, no matter their age or any other risk factors, should have the option to undergo prenatal testing to check for genetic or chromosomal disorders in the unborn baby. This process is known as aneuploidy screening or diagnostic testing. It’s important to note, however, that these tests cannot detect every possible abnormality. These tests should be based on the individual’s risk factors, goals for having children, and personal preferences. Ideally, the option of genetic testing should be discussed during the woman’s first pregnancy check-up.
One type of these tests is called chorionic villus sampling. It might be recommended in a number of situations:
– If early non-invasive prenatal screening or first-trimester combined screening reveals any abnormalities, or if they are detected on an ultrasound.
– If a couple’s previous child had a birth defect.
– If a previous child had an abnormal number of chromosomes, either autosomal (non-sex chromosomes) or sex chromosome aneuploidy (an abnormal number of sex chromosomes).
– If either the mother or father is older.
– If either parent carries a chromosomal rearrangement.
– If either parent carries an abnormal number of chromosomes, or a mixture of normal and abnormal cells (called mosaicism).
– If either parent carries a genetic disorder such as Tay Sachs, Sickle Cell Disease, or Neurofibromatosis.
When a Person Should Avoid Chorionic Villus Sampling
Doctors need to be careful when they perform certain procedures on patients who are using medicines that help prevent blood clots, also known as anticoagulants. This is because these medicines can make it harder for the body to stop bleeding.
One procedure that doctors need to exercise caution with is a test done during pregnancy, especially for moms who have a condition known as alloimmunization. This condition is when the mom’s immune system makes antibodies against the baby’s blood cells, which can lead to the baby having a disease where their red blood cells get destroyed too quickly, also known as hemolytic disease. This condition isn’t an absolute reason not to do the test, but the test might make this condition worse in the baby.
And if the patient has a disease that can be passed on through the blood, like HIV or hepatitis, they need to be informed that there’s a chance the disease could be passed on to their baby during the test.
Equipment used for Chorionic Villus Sampling
The procedure is done with non-stop guidance using ultrasound, a technology that uses sound waves to make live pictures of your body, and follows strict cleanliness measures to prevent infection. Apart from an ultrasound machine, some other tools that your medical team will need include:
Transabdominal Approach:
– A sterile drape: This is an uncontaminated cloth that is used to cover the area of your body where the procedure will take place.
– A sterile ultrasound probe cover: A clean protecting cover that goes over the ultrasound wand to keep it sterile.
– Chlorhexidine or iodine: Both of these are disinfectants – solutions that are applied to the skin to kill bacteria, in order to prevent infection.
– A local anesthetic (optional): This is a type of medication that numbs a small area of your body where a procedure will be done, so you don’t feel pain.
– 10 cc and 20 cc syringe: These are devices used to inject liquid medication or to remove fluid.
– 18 gauge or 20 gauge spinal needle: This is a sharp, thin tool that doctors use to sample tissue or fluid.
– Sample collection container with transport media: This is a sterile bottle or tube that temporarily holds the sample of tissue or fluid that is removed, so it can be analysed later in a laboratory.
Transcervical Approach:
– Sterile speculum: This is a small tool that doctors use to gently open body cavities, such as the vagina, so they can see inside.
– Single tooth tenaculum: This is a device used to gently hold onto tissues during a procedure.
– Iodine preparation: This is a disinfectant solution that is applied to the skin to kill bacteria and prevent infection.
– 10 cc and 20 cc syringe: These are devices used to inject liquid medication or to remove fluid.
– Transcervical CVS catheter: This is a thin tube that is placed into body cavities or vessels to drain or inject liquids.
– Sample collection container with transport media: This is a sterile bottle or tube that temporarily holds the sample of tissue or fluid that is removed, so it can be analysed later in a laboratory.
Who is needed to perform Chorionic Villus Sampling?
The procedure involves a medical professional called a sonographer, who uses a special device to create live images of the inside of your body. These images are called ultrasound scans, which the sonographer captures in real-time (or as it happens). This helps the doctor see what’s going on inside your body without needing to make an incision or use invasive methods.
Preparing for Chorionic Villus Sampling
Before the Procedure:
* You’ll have a formal discussion with a specialist who focuses on pregnancy complications (maternal-fetal medicine specialist).
* If possible, you’ll be referred for genetic counseling while you’re still pregnant. This is to help you understand any risks to your baby’s health.
* You’re given the opportunity to ask questions and weigh the risks and benefits before giving your consent to the procedure.
* If your blood type is Rh-negative, doctors will assess whether you need a medicine called Rhogam to prevent complications.
* An ultrasound will be done to check things like your baby’s heart activity, the size of your baby (measured from crown to rump), where the cord is inserted and where the placenta is located.
* The doctor will make sure all necessary materials are ready, including the medium to transport any samples taken.
At the time of Procedure:
* A skilled healthcare provider and someone who specializes in using ultrasound will be there.
* You’ll be made comfortable on the examination table.
* The lighting in the room will be checked to ensure it is suitable for the procedure.
* Depending on what’s required, either your abdomen or cervix will be prepared.
* If you wish, each step of the procedure will be explained to you by the doctor, this can help reduce anxiety.
How is Chorionic Villus Sampling performed
This excerpt describes two approaches to a procedure known as chorionic villus sampling (CVS). CVS is a test done during early pregnancy to check for birth defects and genetic disorders in the developing baby. It involves taking a small sample of cells, known as chorionic villi, from the placenta, the organ that provides oxygen and nutrients to your baby.
In the transabdominal approach, the medical professional chooses an ideal spot on the belly that provides the best access to the placenta. The area is cleaned with a disinfectant, and then surrounded by sterile covers. The patient lies flat on their back. A local anesthetic, a medication that numbs a specific part of the body, can be used to lessen any discomfort. A thin, hollow needle is inserted with the help of an ultrasound, which is a tool that makes images using sound waves. An ultrasound helps guide the needle to the placenta. After the thin metal rod inside the needle is removed, a syringe filled with a special fluid is connected to it. The needle is then moved back and forth through the placenta while suction is applied to collect a tissue sample.
In the transcervical approach, the patient is placed in a position known as lithotomy, which means lying on their back with legs raised and spread. A sterile tool called a speculum is used to open the vagina; then, the cervix is cleaned with a disinfectant. A small device may be used to hold the cervix steady and assist in passing the catheter, which is a thin tube. Under constant ultrasound guidance, a CVS catheter, a special thin tube, is inserted into the placenta through the cervix. The catheter contains a flexible guide wire that can be seen on the ultrasound. When the catheter is placed correctly, the guide wire is removed, a syringe filled with fluid is attached, and suction is applied to collect a sample.
These tissue samples are then sent to a lab for more testing, which includes checking for chromosomal abnormalities or genetic conditions. The initial results generally come back within 2 to 4 days, but it can take 1 to 2 weeks for complete results. After receiving the results, the patient should discuss next steps with their healthcare provider. They might also need more ultrasounds or a specific blood test to check for further issues. This blood test, known as MSAFP, is used to screen for birth defects of the baby’s brain or spine.
Possible Complications of Chorionic Villus Sampling
Chorionic villus sampling (CVS) is a procedure that checks the health of a baby during pregnancy. Like another similar procedure called amniocentesis, CVS carries some risks. These can include miscarriage, bleeding, infection, rupture of the amniotic sac (the ‘water breaking’ early), and unclear results.
Over time, the risk of miscarriage from CVS has dropped, thanks to better technology and skills of the medics performing the procedure. A review study found that after a CVS procedure, around 0.7% of pregnancies ended in miscarriage within 14 days, 1.3% within 30 days, and 2% at any time during the pregnancy. In comparison, after an amniocentesis procedure, the total miscarriage rate within 14 days was 0.6%.
Factors that can increase the risk of miscarriage after these procedures include the number of times the needle or cathether is inserted, the experience and skill of the doctor, pregnancies achieved through assisted reproductive techniques, and if certain tools like a transcervical cannula (a thin tube passed through the cervix) are used instead of biopsy forceps (a tool used to take tissue samples).
In 1-2% of CVS cases, a condition called confined placental mosaicism can occur. This is when there’s a difference between the genetic makeup of the baby and the placenta (an organ that provides nutrients to the baby). In around 10% of these cases, the baby can also have this genetic difference, which may lead to problems with the placenta functioning and can result in complications for the baby, like slow growth, and for the mother, like high blood pressure. If mosaicism is detected, a follow-up test called amniocentesis is usually recommended in the second trimester of pregnancy.
There are also some rare complications associated with CVS that have been reported, such as limb reduction defects and oromandibular hypogenesis (underdevelopment of the lower half of the face). These are more likely if CVS is performed early in pregnancy, before 10 weeks. The risk of these defects is around 6 in 10,000, about the same as the general population risk. It’s important for patients to know about these potential risks if the CVS is being considered before 10 weeks of pregnancy.
After CVS, up to 32% of women might see some spotting, which is more common when the procedure is done through the cervix. And, though less common, the procedure might sometimes fail to provide a clear result, there may be leakage of the amniotic fluid, or an infection may occur – but this happens in less than 0.5% of cases.
What Else Should I Know About Chorionic Villus Sampling?
Chorionic villus sampling is a trustworthy and proven procedure done early in pregnancy to test for genetic conditions. When done by an experienced healthcare provider and with the use of modern ultrasound technology, the chances of any problems happening are quite low. The information collected from this procedure can assist families in making educated choices regarding their pregnancy.