Advantages and limitations of invasive prenatal diagnosis

Prenatal diagnosis of chromosomal abnormalities comprises cytogenetic analysis of fetal cells obtained after one of the routine invasive techniques, i.e. chorionic villus sampling, placentocentesis, amniocentesis, or cordocentesis. The choice of the type of invasive procedure is primarily based on individual combined calculation of all risk factors of having a chromosomally abnormal child. An important factor for the patient to decide to undergo an invasive procedure is the chance of pregnancy loss as the worst scenario. The problems that can arise in prenatal diagnosis of chromosomal disorders are diff erent types of mosaic forms and diffi culty to distinguish true fetal mosaicism from pseudomosaicism, the risk of missing a subtle anomaly due to the limitation of resolution of light microscopy, and maternal cell contamination. In these cases, some of molecular diagnostic procedures are performed. There is an increasing number of twin pregnancies after stimulation protocols and use of some of the techniques of in vitro fertilization procedures in the infertility treatment. Diff erentiation of monoyzgotic and dizygotic pregnancies is possible by applying microsatellite analysis. Chromosomal discordance in twin pregnancies in most cases is caused by postzygotic nondisjunction, and is recorded both in monozygotic and dizygotic twins. Amniocentesis is the technique of choice, and karyotyping from both amniotic sacs is recommended, especially in cases where one fetus has major structural malformations.

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