First trimester prenatal diagnosis: chorion villus sampling or amniocentesis?
Article Abstract:
Prenatal diagnosis is the detection of congenital defects and genetic disorders in the fetus before birth. Current efforts are focused on improving prenatal diagnosis in the first trimester, or first three months, of pregnancy. The detection of congenital defects or genetic disease can result in a decision to terminate the pregnancy. A first trimester abortion may be safer, easier to perform, more private, and less emotionally distressing than abortion at a later stage in pregnancy. Early prenatal diagnosis may be accomplished by ultrasound, a technique in which sound waves are used to visualize the fetus; maternal biochemical screening, or measurement of markers of disease in the mother; amniocentesis, the sampling of amniotic fluid, which surrounds the fetus; and chorion villus sampling (CVS), the sampling of chorionic villi, a portion of the placenta that is in contact with the wall of the uterus. The detection of structural defects in the fetus can be assessed further by testing for biochemical or cell abnormalities. Advanced age and a history of reproductive problems in the mother increase the risk of fetal abnormalities. Abnormal levels of estriol, human chorionic gonadotropin, and alphafetoprotein are also associated with fetal defects, but these screening tests lack sensitivity (accurate diagnosis) in early pregnancy. Although CVS is a rapid and effective method for detecting fetal defects in early pregnancy, it is not as safe as amniocentesis. Furthermore, differences in the genetic characteristics of the cells in the placenta and the fetus may lead to confusion in diagnosis. Because of these complications, interest has focused on the use of amniocentesis in the first trimester of pregnancy. Amniocentesis, performed before 14 weeks of pregnancy, is technically feasible and safe. However, results obtained by amniocentesis in the first trimester will differ from those obtained in the second trimester due to differences in the structure of the fetal membranes between these two periods of pregnancy. The accuracy, costs, and failure rates of first trimester amniocentesis, and the long-term effects of CVS and amniocentesis in early pregnancy require further study. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: British Journal of Obstetrics and Gynecology
Subject: Health
ISSN: 0306-5456
Year: 1991
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Benefits of placental biopsies for rapid karotyping in the second and third trimesters (late chorionic villus sampling) in high-risk pregnancies
Article Abstract:
Chorionic villus sampling (CVS) is a method of prenatal diagnosis that is usually performed in the first three months of pregnancy. A small sample of tissue from the chorionic villi projections of the placenta are removed for karyotyping, a process of determining the number and configuration of chromosomes. The procedure is safe and the results are rapid and accurate. Although adequate prenatal diagnosis can be obtained by CVS performed in second and third trimester of pregnancy, its use has been limited. Cordocentesis, a direct method of assessing fetal well-being by obtaining blood samples from the fetus' umbilical cord, is the accepted method of late prenatal diagnosis. However, cordocentesis can be technically difficult in pregnancies complicated by abnormal amounts of amniotic fluid, and results take longer to obtain. Fast results may be needed to direct immediate obstetrical decisions. The value of late CVS in diagnosing complications in pregnancies with fetal anomalies and abnormal volume of amniotic fluid, was studied in a total of 301 pregnancies, 225 initially described by suspicious ultrasound. The most common finding (38 percent) on ultrasound was a change in the amount of amniotic fluid; 22 percent of those cases had abnormal findings when CVS samples were karyotyped. Late CVS is useful in providing rapid and accurate results in the presence of suspicious ultrasound imaging of the fetus. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: American Journal of Obstetrics and Gynecology
Subject: Health
ISSN: 0002-9378
Year: 1990
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