Prenatal genetic diagnosis services include numerical and structural chromosomal abnormalities, monogenic diseases and metabolic disorders. The diagnostic procedures used cytogenetic techniques of molecular cytogenetics and molecular analysis of DNA.
The fetal growth and development during pregnancy is analyzed using ultrasound procedures, biochemical (alpha-fetoprotein, triple marker, etc.) and genetic diagnosis. The methods of prenatal diagnosis are applied preferably in the early months of pregnancy, allowing to confirm the normal development of the fetus, as well as to detect the presence of fetal abnormalities.
The prenatal genetic diagnosis term is usually used to demonstrate the presence or absence in the fetus of: chromosomal abnormalities (Down syndrome, Turner or Pateu, and so on), Mendelian disorders (Cystic Fibrosis, Fragile X, and so on), or multifactorial or polygenic malformations (anencephaly, bifide spine, cardiac defects).
The chromosomal abnormalities (chromosomopathy) are detected in 0.5% of all live births, and more than 50% of early spontaneous abortions. The Mendelian and polygenic disorders are found in similar proportions, although it varies among different populations.
Amniocentesis is the removal of a sample of amniotic fluid by introducing a tiny needle (0.7-0.9mm in diameter) in the amniotic sac through the abdomen. The procedure is done with an ultrasound to ensure strict control to avoid harm the embryo. The aspirated volume is 20ml and contains cells exfoliated from the epithelial surface of the fetus.
The earlier period to conduct an amniocentesis is from week 14, and complications after the procedure are rare (eg. Infection of the amniotic fluid, less than 1 case in 1000). Therefore, it is considered a safe procedure.
The fluid sample contained in a syringe is placed in sterile centrifuge tubes inside a laminar flow cabinet for subsequent processing in the laboratory. The supernatant after centrifugation recovered from the liquid is also used for biochemical determinations (eg. alpha-fetoprotein in the diagnosis of Neural tube defects).
The villicentesis involves the extraction of a small biopsy of cells from the chorionic villus (region of the fetal placenta). The sample can be extracted vaginally or through the abdomen. Vaginally using a cervical cannula with a thin polyethylene catheter (diameter 1.5 mm). And through the abdomen it is done with a small needle (0.9mm diameter). Both procedures were performed always under ultrasound surveillance.
There were no significant differences in complications regarding the amniocentesis, although it is important that this procedure is performed by gynecologists specialized in taking such samples. It is carried out between the 9 th -12 th weeks of pregnancy, which helps to make a diagnosis in the first trimester of pregnancy.
The amount of placental tissue obtained is very small (20-30mg), and represents 1/500-1/1000 of the total placental weight, but suitable for propagation in the culture laboratory and subsequent genetic diagnosis.
The cordocentesis is the aspiration of a small amount of fetal blood (~ 1ml), specifically from the umbilical cord, by introducing a thin needle (diameter 0.7-0.9) and under strict ultrasound conditions.
It can be performed after the 18 th week, but it is less common than the other two procedures and held in highly specialized centers.
The blood cells are processed in the culture laboratory and subsequent genetic diagnosis.
Indications for genetic prenatal diagnosis:
Advanced maternal age (over 35 years)
Ultrasound suspicion for abnormal chromosomes
Biochemical essays altered
Antecedents of balanced chromosomopathy in one of the parents
Retardaded intrauterine growth (CIR)
Prior gestation: Fetal death with no established cause, recurrent loss of pregnancy (two or more spontaneous abortions)
Background of genetic diseases in prior children.
Ethnic population at high risk for genetic diseases:
Services Prenatal Diagnosis
|SYNDROME OR GENETIC DESEASE
||TYPE OF GENETIC ANOMALY
|DOWN SYNDROME (TRISOMY 21)
TRISOMY 13, 18, 8
||AMNIOCHIP® (MICROARRAY CGH (aCGH))
|TRANSLOCATIONS (BALANCED OR IMBALANCED)
INVERSIONS (BALANCED OR IMBALANCED)
MOLECULAR-CYTOGENETIC (FISH) (M-FISH)
|MOLECULAR (PCR, SEQUENCING)
|MOLECULAR (PCR, SEQUENCING GRT-PCR)