Prenatal diagnosis is a complex medical act which is the most important for prevention of genetic diseases.

There are four procedures that have entered the current practice: imaging techniques (ultrasound, MRI, radiology), amniocentesis, chorionic villi biopsy and PUBS (percutaneous umbilical cord blood sampling).

The following are the tests most often used for this purpose.

Ultrasound
Easiest technique is the ultrasound prenatal diagnosis. If its use was initially to detect anencephaly, in recent years the “ability” of ultrasound investigations has increased dramatically thanks to better equipment and much better trained experts in fetal medicine.
The first level serves as a screening procedure to determine fetal viability and growth rate. Level I ultrasound monitored pregnancies are not suspected of fetal abnormalities. Detailed ultrasound (level II) is performed when there is a risk for specific abnormalities appearance.

The best time for ultrasound is between weeks 16-18 — on the 18th week of experts can detect about 90% of serious malformations.

Triple test
It is probably the most important noninvasive test performed in order to detect fetal abnormalities such as neural tube defects, Down syndrome, or syndrome Eduards.
It’s advisable to be performed (almost mandatory) on pregnant women over 35 years old, given that the risk of having a fetus with genetic defects increases exponentially after this age (eg Down syndrome, from 1 / 385 at 35 years to 1 / 11 when 49 years old) and also the detection of chromosomal abnormalities in a baby before.

Triple test is a screening method for three markers in maternal serum levels, namely the determination of serum alpha-fetoprotein, unconjugated estriol and chorionic gonadotrophin.

The test requires a minimal amount of venous blood and is performed between 14-21 weeks of gestation.

Of note, the test is indicative value. Most pregnant women who achieve a positive result for trisomy 21 (Down syndrome), trisomy 18 (Eduards syndrome) or neural tube defects can probably have a normal child. Therefore a positive result requires additional diagnostic tests such as an amniocentesis.

For the test to be conclusive, it relies on the correlation between the pregnancy’s age and the quantitative determination of serum markers. It is important to perform an ultrasound before establishing the real gestational age, by fetal biometry.

Amniocentesis
It is a procedure to obtain samples of amniotic fluid by ultrasound-guided trans-abdominal puncture. The amniotic fluid is fetal cells obtained by peeling the skin and mucous membranes and urinary tract. Subsequently cells are subjected to DNA tests to detect mutations or cultivation, in order to obtain chromosome preparations. Along with all these, you can also perform biochemical tests (alpha fetoprotein and acetylcholinesterase) — together with an ultrasound 90% of neural tube defects can be diagnosed before birth.

Amniocentesis tests are performed between 15-17 weeks of gestation. The test has a success rate of about 99%.

Since amniocentesis is an invasive procedure, most women are afraid of miscarriage due to technology. However you should know that the risk of fetal loss is very small — about 0.5%.