Within the prenatal diagnostic tests, chorionic biopsy and cordocentesis are the most invasive, the ones that involve the most risks and the ones that are performed last when making a diagnosis.
Chorionic biopsy (also called chorion biopsy or chorionic biopsy ) consists of extracting a sample from the chorionic villi, which are structures that are part of the placental tissue, and allows fetal alterations to be detected .
How is chorionic biopsy performed?
The technique consists of inserting a needle through the cervix (transcervical) or through an abdominal puncture with local anesthesia (transabdominal), while performing an ultrasound, which allows visualizing the maternal and fetal structures to ensure that the biopsy is done well and without problems.
Both techniques are equally safe and effective, although miscarriage rates are slightly higher when done through the cervix. The choice of one or the other is made according to the location of the placenta and the time of gestation.
Once the sample is obtained, it is sent to the laboratory for study.
It is especially indicated when an increased nuchal translucency or some malformation is detected in the first trimester in the first trimester ultrasound. It is usually recommended in these cases, being always optional:
- If the mother is 35 years old or older: because it increases the probability of giving birth to a child with a congenital defect.
- Child or previous pregnancy with some chromosomal alteration or of another type.
- Family history of genetic defects.
- When in other prenatal tests some important alteration is detected.
- Abnormal first trimester triple screening result .
- When there is a real possibility of risks and you do not want to wait to perform the amniocentesis.
It can also be performed in case of interrupted pregnancy, especially in cases of repeated abortions . In cases of interrupted pregnancy, it will be performed in the operating room at the same time as curettage .
When it’s made?
Chorion biopsy is performed between the 10th and 14th weeks of gestation. The advantage of this test is that it is a quick technique, which allows us to know very quickly if the fetus has any genetic abnormality, much earlier than amniocentesis . The material obtained is analyzed to study the DNA, chromosomes and enzymes of the fetus.
On other occasions, it is also performed as an alternative to amniocentesis in order to study the baby’s karyotype. It is the most useful technique to detect chromosomal abnormalities such as Down syndrome. The efficiency in obtaining a diagnosis is 99.7%. It does not detect neural tube defects such as spina bifida , to detect it an amniocentesis must be performed.
Once performed, the results can be obtained after 48 hours , depending on the techniques requested. The approximate duration of the test is thirty minutes.
What risks does chorionic biopsy have?
Being an invasive test has its risks. Although rare, these include:
- placental hematoma
- rupture of the membranes
- Abortion rate in 1% of cases.
Due to the vaginal method, a slight discomfort is felt as in a vaginal cytology and there may be a small bleeding after performing the procedure.
It does not require prior preparation or hospitalization. Relative home rest is only recommended for the first 48 hours after performing the test.