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Biopsy of the trophoblast: definition of this sample
The trophoblast biopsy, also called choriocentèse, is the name given to the removal of a very small fragment of trophoblast, namely the tissue that surrounds the amniotic pouch and the fetus, and which will become the placenta during the first trimester of pregnancy.
Doctors sometimes speak of a sample of chorionic cells, or of a sample of chorionic villi. We assume that chorion cells have the same origin as fetal cells, and that they therefore have the same genetic characteristics, the same DNA.
This puncture of the trophoblast is usually performed between 11 and 13 weeks of amenorrhea, in other words between the 9th and the 11th week of pregnancy (between 2 months and 2 and a half months).
When is a trophoblast biopsy done?
This examination can be performed for the study of chromosomes of the child (karyotype), for the search for a gene, or for a biological anomaly.
This placenta sample is generally offered by the gynecologist who follows the pregnancy, for various reasons. It may be due to a risk of genetic disease in the family, or observations during the first ultrasound, which may raise concerns about a risk of Down’s syndrome or any other genetic abnormality.
You should know that this exam is not not imposed, but proposed : free to the future parents to accept or refuse it.
Trophoblast biopsy and amniocentesis: what’s the difference?
As the name suggests, a amniocentesis refers to the removal of a little amniotic fluid, while the trophoblast biopsy, or choriocentesis, defines the removal of a small piece of chorion, or future placenta. However, these two examinations have the same goal: to obtain more information about the fetus, about its genetic patrimony (establishment of the karyotype).
The trophoblast biopsy has the advantage of being able to be performed earlier than amniocentesis and of being relatively more reliable. The results can also be obtained faster: for the trophoblast biopsy, the first results are generally obtained within 48 hours, where the results of an amniocentesis are only returned after several days to several weeks depending on the anomaly sought. The interest of the trophoblast biopsy is therefore major for us: we can know and act as soon as possible, especially if we want to proceed with a medical termination of pregnancy (IMG).
Trophoblast biopsy: the course of this examination
An ultrasound is usually performed before the sample is taken to determine the best technique for the patient. Sampling can in fact be carried out in two ways:
- either by a puncture using a fine needle through the belly of the mother-to-be. Local anesthesia is then sometimes necessary. The sample is taken under ultrasound control, by simple aspiration or using a tiny forceps passed inside the needle;
- or, through the cervix like during a pelvic exam. In this case, the puncture itself is usually no more painful than a blood test.
Regardless of the technique used to perform this trophoblast biopsy, it is advisable to stay at resting within hours of the exam.
The risks of this pregnancy test
You should know that even if it is carried out under optimal safety conditions, the realization of a trophoblast biopsy involves a risk of miscarriage estimated at 1 to 2%. It is a small risk, but not negligible. This risk is at its maximum in the 8 to 10 days which follow the withdrawal. Also future parents must weigh the pros and cons of such an examination, and accept the risk (which remains very low) if they choose to have recourse to it.
In view of this low risk of miscarriage, symptoms such as pain, bleeding or discharge of fluid should prompt to seek medical attention.
“In some cases, the technical conditions or the location of the trophoblast are not favorable for performing a trophoblast biopsy, and it may be necessary to postpone the examination for 8 to 10 days, or to schedule an amniocentesis for a few weeks. later so as not to increase the risk of complications”, Also specifies the National College of Obstetrician Gynecologists of France (CNGOF) in its explanatory sheet.
Finally, the CNGOF indicates that, in very rare cases, the sample may fail, or serious infections may occur. These may be favored by the pregnant woman’s history, medication or treatment, etc. This is why it is imperative to inform the doctor of his antecedents (personal and family) and all the treatments and medications that one takes to avoid any complications.
The practical issues surrounding a trophoblast biopsy
If you are about to have a trophoblast biopsy during your pregnancy, you may have some questions and concerns about the practicality of this test. Here are some answers.
On the day of the trophoblast biopsy, it is not no need to be fasting for the sample. It is very important to bring your blood group card, because in the event of negative rh, an injection will be carried out to avoid a rhesus incompatibility with the fetus.
In the hours or days following the sample, it is necessary to consult urgently in the event of loss of blood or fluid, due to the slight increased risk of miscarriage.
The results of the examinations will be communicated by the laboratory to the doctor who prescribed this biopsy, and who will communicate them to you quickly. For a simple karyotype (number and structure of chromosomes), the results are obtained in 48 hours to a few days. For other types of examinations, more extensive, the deadlines are very variable depending on the type of anomaly sought, notes the CNGOF.
Finally, know that the trophoblast biopsy, since it is prescribed by the medical profession, is 100% covered by Social Security, with exemption from advance fees (third party payment). By bringing your vital card and your health insurance card, you will not have to pay anything.
sources:
- http://www.cngof.fr/ressources-pedagogiques/videos/interventions-gynecologie/240-cngof-2009-tc-biopsie-de-trophoblaste
- http://pitiesalpetriere.aphp.fr/wp-content/blogs.dir/179/files/2015/06/INFO-BIOPSIE-DE-TROPHOBLASTE-CNGOF.pdf