The term diagnos prenatal stico groups all those diagnostic action to discover during pregnancy a birth defect, defined as, and as defined by the World Health Organization, "any anomaly morphological development, structural, functional or molecular present at birth (although it may manifest later), external or internal, familial or sporadic, hereditary or not, single or multiple. "
Purpose of prenatal diagnosis and types of detectable abnormalities
Prenatal diagnosis intended to diagnose with greater precocity a possible birth defect or establish their absence, as the confirmation of normality helps reduce maternal anxiety during the remainder of gestation.
About 3% of live births have some kind of anomaly, but this figure increases to 4-7% in the first year of life.
These anomalies are divided into:
- structural abnormalities or defects, which occur in 1-2% of pregnancies and accounts for 25% of congenital anomalies.
- hereditary diseases that occur in the 1-1.5% of pregnancies and involve most fetuses with a birth defect.
- chromosomal abnormalities, affecting almost 1% of fetuses and responsible for 15% of birth defects.
Techniques and advances in prenatal diagnosis and pathology má s common
Given the economic cost of prenatal diagnostic techniques, and the fact that some of them carry a risk of fetal loss (invasive techniques), it is necessary to establish criteria that do not allow to select those pregnancies at increased risk for a birth defect , constituting the so-called "risk".
The strategies are intended to diagnose Anomali as chromosomal micas (called aneuploidy) and, mainly, the Yes ndrome Down syndrome (trisomy 21) are those that in recent decades have seen major advances and changes aimed at selecting this "population risk". By invasive techniques offer a possible prenatal diagnosis and the possibility of a legal termination of pregnancy in accordance with current legislation.
Within chromosomal abnormalities, the most common is the Trisom ed 21 (about 1 in 700 pregnancies), also called Yes ndrome Down, followed by trisomy 18 (1 every 3000-5000 pregnancies) or Yes ndrome Edwards, and Trisomy 13 (1 in 8,000 to 15,000 pregnancies) or Patau ndrome. Note that these last two are incompatible with life. There are also anomalies affecting sex chromosomes, with the Yes ndrome Turner (affects female fetuses) and Yes ndrome Klinefelter (affecting males) the most common of this group (1 per 1,000 pregnancies approximately).
Innovation in the diagnosis: non - invasive prenatal test
Currently, and after many years of research, it is available in Gynecology and Obstetrics a new diagnostic test to detect free fetal DNA in maternal blood, which provides an estimate of the risk that has the fetus to be affected by Trisomy 21 , Trisomy 18 and Trisomy 13. It is a diagnosis Prenatal noninvasive (DPNI), still limited to certain chromosomes and therefore does not offer as much information as you would get with an amniocentesis or chorionic villus sampling, which all chromosomes are investigated (fetal karyotype ).
In those positive cases (high risk) for chromosomal abnormalities with it are detected, the abnormality should be confirmed by an invasive technique such as amniocentesis, because, although its sensitivity is 99.5% (ie, detects virtually all of chromosomal abnormalities in chromosomes above), its specificity is not as high, with a false positive rate of 0.04% for trisomy 21 and can reach 1% for trisomy 13 and 18, which can create anxiety in a group of pregnant until confirmation or not the final result.
Despite the advantages of this test (sensitivity practically 100% and very low false positive rate), it does not replace the current screening strategy first quarter is presently required, but it is a supplement that has utility in specific cases, for example, intermediate risk screening or first quarter of maternal anxiety low risk. In cases of high risk in first trimester screening would be invasive technique (Corial Biopsy or Amniocentesis) the first indication.
Although the test DIAGNO Prenatal stico noninvasive (DPNI) is in clinical use in our country about two years ago, it is beginning to have results that make foresee that it will be a technique to consider in prenatal diagnostic tests and it will avoid many invasive techniques, when its price, still high, make it a more affordable test.
We must also say that, although in some public hospitals in Spain begin to use it in very indicated cases is still no test available to the public medicine in our country.
Edited by Roser Berner Ubasos.