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Amniocentesis is an invasive procedure in which a needle is passed through the mother's lower abdomen into the amniotic cavity inside the uterus. Enough amniotic fluid is present for this to be accomplished starting about 14 weeks gestation. For prenatal diagnosis, most amniocenteses are performed between 14 and 20 weeks gestation. However, an ultrasound examination always proceeds amniocentesis in order to determine gestational age, the position of the foetus and placenta, and determine if enough amniotic fluid is present. Within the amniotic fluid are foetal cells (mostly derived from foetal skin) which can be grown in culture for chromosome analysis, biochemical analysis, and molecular biologic analysis. Risks with amniocentesis are uncommon, but include foetal loss and maternal Rh sensitization. The increased risk for foetal mortality following amniocentesis is about 0.5% above what would normally be expected.
In Chorionic Villi sampling procedure, a catheter is passed via the vagina through the cervix and into the uterus to the developing placenta under ultrasound guidance. Alternative approaches are transvaginal and transabdominal. The introduction of the catheter allows sampling of cells from the placental chorionic villi. These cells can then be analyzed by a variety of techniques. The most common test employed on cells obtained by CVS is chromosome analysis to determine the karyotype of the fetus. The cells can also be grown in culture for biochemical or molecular biologic analysis. CVS can be safely performed between 9.5 and 12.5 weeks gestation. CVS has the disadvantage of being an invasive procedure, and it has a small but significant rate of morbidity for the fetus, this loss rate is about 0.5 to 1%. The possibility of maternal Rh sensitization is present. There is also the possibility that maternal blood cells in the developing placenta will be sampled instead of fetal cells and confound chromosome analysis.
In situ is a technique for culture and analysis of adherent cells in Cytogenetics prenatal field. The primary advantage of using the In situ method in stead of in T-Flask is that it provides information about the colony of origin of a cell. This is important when deciding whether an abnormality seen in some but not all cells represents true mosaicism (constitutional mosaicism) or an artifact of tissue culture (pseudo mosaicism). No inference can be made about the origin of cells when using the flask method, because cells from all colonies are mixed together after they are released from the growing surface. It is impossible to tell if multiple cells exhibiting the same chromosomal abnormality arose from one or multiple colonies. Another advantage of the in situ method is that there is usually a shorter turnaround time because only primary cultures are harvested. Flask cultures are often subcultured, adding days to the culture time.
In Chorionic Villi sampling procedure, a catheter is passed via the vagina through the cervix and into the uterus to the developing placenta under ultrasound guidance. Alternative approaches are transvaginal and transabdominal. The introduction of the catheter allows sampling of cells from the placental chorionic villi. These cells can then be analyzed by a variety of techniques. The most common test employed on cells obtained by CVS is chromosome analysis to determine the karyotype of the fetus. The cells can also be grown in culture for biochemical or molecular biologic analysis. CVS can be safely performed between 9.5 and 12.5 weeks gestation. CVS has the disadvantage of being an invasive procedure, and it has a small but significant rate of morbidity for the fetus, this loss rate is about 0.5 to 1%. The possibility of maternal Rh sensitization is present. There is also the possibility that maternal blood cells in the developing placenta will be sampled instead of fetal cells and confound chromosome analysis.
In situ is a technique for culture and analysis of adherent cells in Cytogenetics prenatal field. The primary advantage of using the In situ method in stead of in T-Flask is that it provides information about the colony of origin of a cell. This is important when deciding whether an abnormality seen in some but not all cells represents true mosaicism (constitutional mosaicism) or an artifact of tissue culture (pseudo mosaicism). No inference can be made about the origin of cells when using the flask method, because cells from all colonies are mixed together after they are released from the growing surface. It is impossible to tell if multiple cells exhibiting the same chromosomal abnormality arose from one or multiple colonies. Another advantage of the in situ method is that there is usually a shorter turnaround time because only primary cultures are harvested. Flask cultures are often subcultured, adding days to the culture time.