Popularly known as chorionic villus sampling, it is an invasive procedure performed for first trimester prenatal diagnosis.
In this procedure, tissue from the villi (vascular fingers) of the chorion, a part of the placenta, is removed and examined.
Before 9 weeks, the chorionic villi cover the entire external surface of the gestational sac.
As growth continues, the developing sac begins to fill the uterine cavity, and most villi regress except at the implantation site, where they associate with the decidua basalis.
The villi in this area proliferate rapidly to form the leafy chorion.
Between 9 and 12 weeks’ gestation, the villi float freely within the intervertebral space blood and only loosely anchor to the underlying decidua basalis.
Chorionic villi are of fetal origin and are an appropriate and useful source of tissue for the evaluation of fetal genetic disease.
Its cytogenetic, molecular, and biochemical properties mirror those of the fetus.
The villi are composed in part of cytotrophoblast cells, which are a source of actively dividing spontaneous mitosis and can be used for rapid chromosome analysis .
The chorionic biopsy can provide information on chromosomal conditions of the fetus, the chorionic villi are composed of placental tissues that have the same genetic makeup as the fetus.
Generally, the sampling is carried out in the period between 10 and 13 weeks of pregnancy.
With the help of chorionic biopsy the presence of chromosomal conditions such as:
- Down syndrome.
- Trisomy 13.
- Trisomy 18.
- Sex chromosomal abnormalities such as Turner syndrome.
- Cystic fibrosis.
- Sickle cell anemia
- Tay-sachs disease.
Not all chromosomal or genetic defects, such as spina bifida and other neural tube-related defects, can be identified by chorionic biopsy.
Chorionic biopsy may be considered in cases such as:
- If you have had positive results from a prenatal screening test. If the results of a screening test, such as the first trimester test or the prenatal cell-free DNA test, are positive or of concern, you may choose to have chorionic villus sampling to confirm or rule out a diagnosis.
- If you have a chromosomal condition in a previous pregnancy. In those cases in which the patient has had a pregnancy affected with Down syndrome or some other chromosomal condition, the new pregnancy presents a higher risk.
- Be over 35 years of age. Babies born to mothers over the age of 35 have a higher risk of developing chromosomal diseases.
- Possessing a family history or being the parents known to be carriers of a specific genetic condition.
To recommend a chorionic biopsy, ultrasound will be used to determine the gestational age of the baby and the position of the placenta.
The procedure for obtaining the sample can be performed through the cervix or the abdominal wall, with the help of an ultrasound image that will serve as a guide to take the tissue sample from the placenta.
- Transabdominal chorionic villus sampling: This is done by inserting a needle through the abdominal wall into the uterus.
- Transcervical chorionic villus sampling: This is done through the vagina by inserting a tube up to the cervix to suction and obtain a small tissue sample when the catheter reaches the placenta.
If an adequate amount of tissue cannot be obtained on the first attempt, the procedure may need to be repeated.
The tissue sample obtained will be analyzed in a laboratory.
Occasionally, test results are unclear and an amniocentesis, another prenatal diagnostic test, is needed to clarify the diagnosis.
After the procedure, slight vaginal bleeding may occur when the tissue sample is removed. It is necessary to monitor the heart rate of the fetus.
A normal level of activity can be resumed after the procedure, avoiding strenuous physical activity.
Sexual activity should be avoided for a day.
It is necessary to see a doctor immediately in the following cases:
- Present fluid that leaks from the vagina.
- Present heavy bleeding.
- Have a fever.
- Present uterine contractions.
If chorionic villus sampling indicates that your baby has a chromosomal or genetic problem that cannot be treated, important decisions may need to be made, such as whether or not to continue the pregnancy.
When chorionic villus sampling is transcervical (performed through the vagina), it is not recommended in the following cases:
- The presence of an active cervical or vaginal infection, such as herpes.
- The presence of vaginal bleeding or spotting in the previous two weeks.
- When an inaccessible placenta occurs, due to a tilted uterus or non-cancerous growths in the lower part of the uterus, such as uterine fibroids.
When chorionic villus sampling is transabdominal (performed through the abdominal wall), it is not recommended when there is:
The uterus is upside down and the placenta is at the back of your uterus.
Chorionic villus sampling carries a number of risks, including:
Miscarriage: The risk of miscarriage after chorionic villus sampling is approximately 7 percent. This risk of can be increased in the cases of fetuses that present / display a size smaller than what is normal for their gestational age.
Rh sensitization: Rhesus factor (Rh) is an inherited trait that refers to a specific protein found on the surface of red blood cells. When there is a risk of incompatibilities, the use of both types of chorionic villus sampling is not recommended.
In the event that the mother is Rh negative, and the baby is Rh positive, there is a production of Rh antibodies and the bleeding caused by these types of procedures could enter the bloodstream and increase the response of these antibodies, causing complications for the fetus.
Through a blood test it can be detected if antibodies have begun to be produced and if positive immunoglobulin is administered after chorionic villus sampling.
Infection: Chorionic villus sampling can trigger a uterine infection , in rare cases.
Malformations: there have been cases of chorionic villus sampling that have caused defects in the fingers and toes of the fetus, when the procedure is carried out before the tenth week of gestation.