Prenatal and preconception diagnosis
Prenatal diagnosisThe techniques used in prenatal diagnosis include instrumental laboratory investigations developed over the last 50 years with the objective to underline problems of genetic nature, starting from the first phases of the post-implant embryonic development, up to the moments that precede the birth. The techniques can be more or less invasive and can be performed in different phases during the pregnancy. These techniques mainly comprise the prenatal echography, the non invasive screening on peripheral maternal blood (NIPT, Non Invasive Prenatal Testing), chorionic villus sampling (CVS) and amniocentesis.
It is possible to verify both the uniformity of the number and the structure of the chromosome, and the presence of specific monogenic illnesses from which the molecular defect is known.
The prenatal echography, namely the monitoring of the pregnancy through ultrasounds, is the most important and diffused non-invasive technique for prenatal diagnosis. This echography is employed to monitor the fetus’ development, to verify the conformity of the fetus and the consolidated morphological parameters, to act as a "bell of alarm" for possible invasive investigations that demand the acquisition of fetal tissues. This technique that is not invasive, allows the reiteration in pre-arranged phases throughout the pregnancy. Besides, the most modern equipment available guarantees an elevated degree of resolution and therefore justifies the extraordinary distribution throughout industrialized countries as a first level of prenatal screening. It is obviously subject to variability of resolution depending on the equipment used and the experience of the operator.
Amniocentesis is an invasive technique mostly used for prenatal diagnosis (>100.000 samples per year in Italy), finalized to the echo-driven acquisition and through trans abdominal puncture of the amniotic liquid. It is carried out ideally around the 15°-16° week of gestation. A risk of abortion exists, and it is due to the nature of the invasive technique, estimated around 0.5% of all samples, but broadly variable in relationship to the experience of the operator. It allows the examination of the fetal cells and the verification of its karyotype, and at the same time the analysis of several chemical substances produced by the organism of the future new-born with the purpose to verify it’s metabolic functions. In order to check some genetic (syndrome of Down) anomalies, amniocentesis is recommended in the presence of previous prenatal screening tests that include anomalous results, chromosomal anomalies in a previous pregnancy, maternal age above 35 years, history of family genetic illnesses.
CVS is an invasive technique used for the trans-abdominal (from the womb) and trans-cervical (from the vagina) collection of some cells of the trophoblast (>25.000 samples/year in Italy). This has the advantage to be performed in an earlier stage in comparison to the amniocentesis, generally between the 11° and the 13° week of gestation. The side effects are: cramps, spotting and in around 1% of the cases, the abortion, all as a result of the invasiveness of the technique. The result of the collecting varies meaningfully depending on the experience of the operator.
The non invasive prenatal tests of the circulating fetal DNA represent an important screening of new conception, allowing to avoid unnecessary invasive prenatal techniques. In fact they offer an accurate (sensibility above 99%) result regarding the most common human autosomal trisomy. Specifically, today, thanks to the most recent technological progress, specialist laboratories are able to isolate circulating fetal DNA from a sample of peripheral maternal blood and to evaluate its chromosomal profile. The test is practicable starting from the 10° gestational week, but it is advisable to combine it to an obstetric echography around the 12° week.
In Valle Giulia Clinic, it is possible to perform the following non invasive prenatal test:
- NACE®: Non-invasive Analysis for Chromosomal Examination
Preconception DiagnosisToday, there is the possibility to allow a wide screening during the pre-conception phase and therefore investigate the risk to be carriers of transmissible genetic illnesses, generally defined as carrier screening. This is a genetic test that allows the comprehension of our own status of healthy carrier of the recessive genetic illnesses or X-linked which are more frequent in the Italian population (for example: cystic fibrosis, Mediterranean anaemia, SMA, X-fragile, etc.), and can have serious consequences on the quality of life of the baby. By identifying the mutations in the gene-illness of which the couple is the healthy carrier, the test allows to put strategies to prevent the transmission of the disease, these strategies may be the pre-implantation testing on the blastocysts obtained after in-vitro fertilization (IVF) or the prenatal diagnosis. It can be carried out in whatever moment before the start of the pregnancy, with a sample of saliva or blood, withdrawn using a special device found in the kit. The result will be available with an enclosed comment in 3 working weeks and it is recommended that is accompanied by genetic consultation.
All the couples who are programming a pregnancy, both naturally and through assisted reproductive technology, homologous or heterologous, can ask for a close genetic examination that goes on to replace and to implement the Cystic Fibrosis test which is commonly performed in the pre-conception phase before the beginning of the IVF cycle.