Which women have to undergo a villocentesis?
In public facilities, women aged 35 or over (on the presumed date of childbirth), together with pregnant women who have an indication foreseen by the national protocol, can undergo free consultation with genetic counseling.
Villocentesis is the exam of choice to recognize diseases of chromosomes or genes within the first 3 months of pregnancy. It is therefore advisable if the couple is at high risk for these diseases (previous children or affected family members, advanced maternal age, etc.) or if the fetus after ultrasound (nuchal translucency) and bi-test, turns out to be positive for screening (therefore ad " high "risk of chromosomal abnormalities).
How soon will I receive the results of the villocentesi? How reliable are they?
Preliminary information is available after two or three days from the villocentesi, while for the definitive report it is necessary to wait 10-15 days. The different waiting times reflect two different analytical techniques of the placental sample, which whenever possible are always performed together.
Chromosomal analysis must be performed on cells in division and, in the case of chorionic villi, two methods of investigation are used: the direct method for early diagnosis and cell culture to optimize diagnostic reliability. After sampling by villocentesis, the sample is then divided into two aliquots; one part is used for direct analysis, the other for analysis after culture.
The direct method exploits the spontaneous divisions of the drawn cells; each of these cells, dividing several times, gives rise to daughter cells with the same chromosome set.
With the culture method, on the other hand, the cells are sown on a special glass and incubated, so as to favor their multiplication and originate the relative colonies (aggregates of cells with the same chromosomal outfit of the original cell). After a few days, when the colonies are sufficiently numerous, the chromosome will be examined.
In the absence of a sufficient amount of chorionic villi it is not possible to prepare both preparations. All this reduces the diagnostic reliability of the villocentesis, because the sampling can be contaminated by cells of maternal origin; therefore, the purpose of the culture is to eliminate the risk of analyzing maternal rather than fetal cells, with the consequent danger of false negatives. Only the study of a high number of cells can in fact make it possible to avoid a diagnostic error.
By relying once again on statistical data, in two cases out of a thousand samples it can happen that the cell culture does not develop enough to allow a definitive diagnosis. In this case, after 2-4 weeks, it may be necessary to repeat the villocentesis, even if in most cases it is decided to take an amniotic fluid. These and other investigations may be necessary even when the analysis leaves doubts of interpretation (3 cases out of 100).
Although they are particularly small (we speak of one case every 500-1000 examinations), the possibility of false positives, or the risk of a diagnosis of abnormalities in healthy fetuses, should not be excluded. On the other hand, despite the apparent absence of anomalies, at birth the child could show genetic defects not detectable by studying chorionic villi. In fact, many malformations are not associated with chromosome abnormalities, and may eventually be observed only with an accurate ultrasound examination between the 19th and 22nd week of pregnancy. There may then be problems concerning the anatomy, or other organism functions that cannot be recognized before birth.
Villocentesi: when to undergo the examination?
Villocentesis is performed after the 10th gestational week, since in previous periods there is the risk of fetal injury; in fact an association between villocentesis performed before the 9th week and appearance of congenital fetal defects, such as limb anomalies (1.6% at 6-7 weeks, 0.1% at 8-9 weeks) was indeed highlighted.
Normally, therefore, the villocentesis is performed between the 11th and 13th week of pregnancy; when necessary, it can still be realized in subsequent periods.
Villocentesi or amniocentesis?
The main advantage of villocentesi compared to amniocentesis lies in the possibility of performing the examination at an early age, despite the fact that amniotic fluid withdrawal is now possible even between the 11th and 13th week (as a rule it is performed between the 15th and 18th, therefore at the beginning of the third trimester of pregnancy). Furthermore, villocentesis offers the possibility of reducing waiting times for diagnostic results. Therefore, in the presence of a serious pathology of the fetus, thanks to the villocentesis, the couple may decide to interrupt the pregnancy at an early age, with less physical and mental stress.
Villocentesis is more suitable for the study of possible genetic diseases, while amniocentesis is more suitable for couples at risk of chromosomal diseases or for the diagnosis of fetal infections.
As anticipated, the abortive risk related to villocentesis (1%) is very similar to the one on amniocentesis (0.5-1%). Among the conditions that orientate towards an early diagnosis by means of villocentesis we note the presence of positive first-trimester screening (duo test, plica nucale), advanced maternal age and favorable position of the placenta.
It should be remembered that unlike amniocentesis, villocentesis does not provide information on the risk of neural tube closure and abdominal wall defects (because it does not allow the determination of alpha-fetoprotein). It will therefore be important to recommend the patient to carry out an ultrasound scan to study fetal anatomy at 20-22 weeks, with particular attention to the morphology of the spine and abdomen.
If the villocentesi shows fetal anomalies, what is the maximum term for the termination of the pregnancy?
According to the law regulating the voluntary interruption of pregnancy (Law 194/78), the request for interruption for the expectant mother, who is diagnosed with a serious fetal anomaly after the first 90 days and in any case before the 22nd week of gestation, is subject to to the medical ascertainment of the condition of serious threat to the mental health of the pregnant woman constituted by the continuation of gestation.
