The definitive diagnosis of malformations such as Trisomies 21, 18 and 13 can only be done through invasive tests such as amniocentesis or villus biopsy done.
The risk of a fetus develop various malformations, such as Trisomies 21, 18 and 13 can be evaluated using the combined first trimester Screening, whose result is expressed as high or low risk, thus allowing for the parents, with the attending physician, make an informed decision in favor or not of the invasive exam.
The Trisomy 21 (Down syndrome) is a genetic alteration, caused by the presence of an extra chromosome 21, by which patients exhibit morphological alterations and organic, as nasal hypoplasia, very wide space between the first and second finger, palmar crease, as well as cardiac malformations and changes.
The Trisomy 18 (Edwards syndrome) is caused by the presence of a chromosome 6:00 pm and in these cases the fetus presents typical morphological features such as mental retardation, heart and renal malformations, diaphragmatic hernia, among others. For your time, Trisomy 13 (Patau syndrome) is caused by the presence of a chromosome causes mental retardation and 1:00 pm sharp and heart defects, renal and serious eye. In these cases, the majority of newborns dies in the first month of life or in the first 6 months.
According to the Fetal Medicine Foundation (FMF), an organization that promotes research in the field of Fetal Medicine, combined first quarter screening that combines the echographic exams and biochemist, features a 97% detection rate with only 3% false positives, i.e., positive diagnosis and absence of anomaly, and thus a very important element to be taken into account by , in the decision to perform an amniocentesis.
The definitive diagnosis of malformations referred to can only be done through invasive tests such as amniocentesis or villus biopsy done. Amniocentesis involves obtaining a sample of amniotic fluid through a puncture in the abdominal wall of the mother guided by an ultrasound so that the doctor can drive the needle accurately, without risk of damage to the fetus or placenta. Amniotic fluid contains cells of the baby, which will allow the study of chromosomes.
The villus biopsy done allows diagnostic prenatal chromosome and consists, instead of amniotic fluid (amniocentesis), on the extraction of a small sample of the villi of the Chorion, i.e. a sample of the placenta. Are so invasive methods, which require the introduction of a needle into the uterus and entail risks of miscarriage (0.5 to 1.0%). Should only be performed in pregnancies considered at risk for chromosomal defects, duly identified by the doctor after the echographic exams and biochemist.