Villocentesis (assessment exams)

Content

Introduction

The villocentesis is an invasive examination that consists in the removal of a small portion of chorionic villi, small offshoots of the forming placenta deriving from the fertilized egg and equipped with the same genetic heritage as the embryo. The tissue taken is subjected to laboratory analyzes that allow to build the chromosome map of the fetus to ascertain (diagnose) any congenital anomalies (such as Down syndrome, Patau syndrome or Edwards syndrome) or genetic diseases (such as cystic fibrosis, Duchenne-Becker muscular dystrophy, thalassemia, phenylketonuria).

The villocentesis is performed between the 10th and 13th week of pregnancy, a few weeks before the amniocentesis, another test that can be performed before birth to ascertain the presence of congenital or genetic diseases. in cases, the sampling is carried out by introducing a fine needle through the maternal abdomen (trans-abdominal access); more rarely, by introducing a small tube through the vagina and the cervical canal (trans-cervical access) to enter the uterus cavity and reach the forming placenta. The operator who performs the procedure chooses the most appropriate route to carry out the sample by chance, taking into account the position in which the embryo is implanted.

CVS is recommended: for women who have had positive results in other tests for prenatal diseases (prenatal screening) such as the combined test, the bi test, or the tri test; to women with a previous child suffering from chromosomal diseases; to women over the age of 35 who have not performed the prenatal screening tests provided for in the first trimester of pregnancy; in the presence of family members with specific genetic diseases or if one or both parents are recognized carriers of a genetic disease.

The results allow, in 99% of cases, to exclude or ascertain (diagnose) numerous genetic diseases, even if they cannot identify all the possible diseases of the fetus. Very rarely the results of CVS are not clear and require, to obtain a certain diagnosis, to perform an "amniocentesis. Regardless of the medical indications, the couple is always free to decide whether or not to resort to prenatal diagnosis.

CVS carries an additional risk of miscarriage between 1% and 2% compared to the miscarriage risk that each pregnancy has. The risk of miscarriage associated with performing the test is slightly higher for CVS than for CVS. "amniocentesis. For both tests, the experience of those who perform the procedure can influence the risk of abortion.

The test

CVS is performed in the clinic and does not require any special preparation, antibiotic prophylaxis is not recommended before the procedure is performed.

First the operator determines with the ultrasound the gestational period of the pregnancy and the position of the implantation of the embryo. Subsequently, the ultrasound is used to guide the sampling of the chorionic villus.

If the sample is taken through the abdomen (transabdominal route), which is the most frequent modality, the operator disinfects the skin (skin) of the maternal belly and uses a local anesthetic to numb the point where the needle will be inserted. Then, under ultrasound guidance, the operator inserts a long, thin needle through the belly (abdominal wall) until it reaches the inside of the uterus. Then, with a syringe, he takes a small amount (sample) of tissue from the chorionic villi, which will be analyzed later, and removes the needle.

If the sample, on the other hand, is carried out passing through the vagina and the neck of the uterus (via trans-cervical), an instrument (speculum), made of metal or plastic, is used to widen the walls of the vagina and visualize the neck of the " uterus. Under ultrasound guidance, a tube connected to a syringe is inserted to pass through the vagina and cervical canal, previously disinfected with an antiseptic solution, and is continued to the implant site to collect a small amount of chorionic villus tissue, to be analyze later.

At the end of the sampling, the heartbeat of the fetus is rechecked with ultrasound. Most women describe CVS as annoying rather than painful. Pap smear. Both techniques are safe and the choice is made by the doctor after evaluating various factors including the position of the embryo and the forming placenta.

Generally, the woman is kept under observation for about an hour after the blood collection, especially to check for any blood loss that may occur immediately after the investigation, and then she can go home.In the case of a bicorial twin pregnancy, ie with 2 amniotic sacs that contain the two embryos and their respective placentas, it is preferable to resort to amniocentesis because performing two samples increases the risk of abortion.

If the mother is Rh negative blood type, anti-D immunoglobulin prophylaxis is recommended to prevent the formation of antibodies directed against the blood cells of the fetus.

After the villocentesis it is advisable to rest, avoiding efforts for at least 24 hours, and to follow the instructions of your doctor who could schedule a control ultrasound after a couple of days from the examination.

In the event of fluid leakage, or significant bleeding from the vagina, severe abdominal pain, uterine contractions or fever, you should contact your doctor as quickly as possible.

CVS results in an increased risk of spontaneous abortion due to the "test" and a risk of uterine infections. The additional risk of spontaneous abortion is partly related to the experience of the person performing the procedure and is difficult to quantify: some studies suggest that it is higher for villocentesis performed trans-cervically than for trans-abdominal, which would, on the other hand, a risk comparable to that of amniocentesis. Globally, on the basis of the evidence available to date, it is considered to be between 1-2%. The risk of uterine infection is less than 1 in every 1000 women who undergo CVS.

The risk of CVS causing complications is greater if it is performed before the 10th week of pregnancy and it is for this reason that the test is performed only after this gestational period.

Results

There are several types of laboratory analyzes (tests) available to study the genetic makeup of the child.The fastest ones, with results provided in a few days, allow you to identify any alterations in the number of some chromosomes and allow you to ascertain (diagnose) the presence of Down syndrome (trisomy 21, caused by an excess chromosome 21), Edwards (trisomy 18, caused by an extra chromosome 18) and Patau syndrome (trisomy 13, caused by an extra chromosome 13). In case of request for more detailed tests, which allow to ascertain (diagnose) a large number of diseases caused by submicroscopic gene alterations, it may take up to two or three weeks to obtain the examination result.

The results provide a "yes" or "no" answer. For most women undergoing CVS the result will be negative, meaning that the fetus is not affected by any of the genetic diseases investigated. If the result is positive, however, it means that the fetus has one of the conditions for which the test was performed. In this case, the implications of the result will be discussed with the couple to help them evaluate the best decision to make. . For most genetic diseases, unfortunately, there is no cure. If you decide to continue the pregnancy it is advisable to use the support of health professionals to choose the most appropriate place for the birth and to arrange any specific treatments for the needs of the baby. If you decide to terminate the pregnancy, by means of a therapeutic abortion, you will receive information on where and how to carry out the surgery according to the week of pregnancy.

In 1 case out of 100 it may happen that the result of the examination is not clear.This may be because the tissue sample taken is insufficient to perform the necessary laboratory tests or because the results suggest the possibility that an abnormality found is present in the chorionic villi, but not in the fetus. In these cases it is good to talk to a geneticist. It may be necessary to have amniocentesis, after a few weeks, to confirm the diagnosis.

Before undergoing techniques, such as villocentesis or amniocentesis, to ascertain the presence of diseases before birth (prenatal diagnosis test), an interview is scheduled with an expert doctor who will provide the couple with detailed information on:

  • what are the diseases that can be ascertained (diagnosed) with CVS and amniocentesis
  • which test (amniocentesis or CVS) is recommended in your case
  • the types of laboratory tests available and the meaning of the results
  • the reliability of laboratory tests
  • the risk of having an uncertain result and having to repeat the procedure
  • the risk of abortion linked to the examination, including the risk identified in the clinical center where the test will be performed
  • the time it takes to get the results
  • the options available if the fetus has one of the genetic conditions sought by the test

Bibliography

United Kingdom Government. Screening in pregnancy: CVS and amniocentesis information for parents (English)

Royal College of Obstetricians and Gynaecologists (RCOG). Amniocentesis and Chorionic Villus Sampling. RCOG Green Top Guideline. 2010; 8

Ghi T et al, on behalf of the International Society of Ultrasound in Obstetrics and Gynecology. ISUOG Practice Guidelines: invasive procedures for prenatal diagnosis in obstetrics. Ultrasound in Obstetrics and Gynecology 2016;48:256-68

American College of Obstetricians and Gynecologists "Committee on Practice Bulletins — Obstetrics, Committee on Genetics, Society for Maternal-Fetal Medicine. Practice Bulletin No.162: Prenatal diagnostic testing for genetic disorders. [Summary]. Obstetrics and Gynecology 2016; 127: e108

Alfirevic Z et al. Amniocentesis and chorionic villus sampling for prenatal diagnosis. Cochrane Database Systematic Review. 2017; 9: CD003252

In-depth link

SaPeRiDoc. Prenatal diagnosis of genetic diseases

Mayo Clinic. Chorionic villus sampling (English)

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