Interpretation of chorionic villus sampling laboratory results is just as reliable as amniocentesis

Article Abstract:

Amniocentesis is a prenatal test performed around the 16th week of pregnancy (during the second trimester of pregnancy), to detect chromosomal fetal abnormalities. A sample of fluid surrounding the fetus contains fetal cells which can then be analyzed in the laboratory. The procedure is safe, reliable and has very few complications. Chorionic villus sampling (CVS) is a new method that removes fetal tissue during the first three months of pregnancy. The results of CVS are obtained faster, affording patients more privacy, because the procedure is done before pregnancy becomes obvious, which allows decisions regarding termination of abnormal pregnancies to be made earlier. The safety of CVS approaches that of amniocentesis. For chorionic villus sampling to be accepted as a reliable alternative to the standard amniocentesis, the accuracy of laboratory results must be replicated. The laboratory results of cytological examination of cells obtained from amniocentesis and chorionic villi sampling were compared over a two-year period. The fetal cells can be analyzed directly or after the cells have been cultured in the laboratory, in case the initial results need to be verified by additional studies. More studies were required in 1.2 percent of the chorionic villus samples and 0.75 percent of the samples obtained from amniotic fluid. Both methods were weak in different areas of cytogenetic analysis. Although the number of cases with uncertain results was slightly higher with chorionic villus sampling, the differences were not significant. Since the safety and efficacy of chorionic villus sampling have improved, the accuracy of laboratory analysis makes the procedure a viable alternative to amniocentesis. (Consumer Summary produced by Reliance Medical Information, Inc.)

Analysis, Karyotypes, Amniocentesis, Fetal tissues, Chorionic villus sampling

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The inadequacy of the current correction for maternal weight in maternal serum alpha-fetoprotein interpretation

Article Abstract:

A high level of alpha-fetoprotein in the blood of a pregnant woman is highly suggestive of a neural tube defect (defects such as inadequate closure of the tube surrounding the spinal cord and nerves at the base of the brain) in the fetus. Fetuses suspected of neural tube defects are evaluated further by amniocentesis and ultrasonography. Since race, diabetes and maternal weight can affect standard values, the levels of maternal serum alpha-fetoprotein (MSAFP) are adjusted to improve the accuracy of this predictive tool. Mothers who weigh more are thought to have larger blood volumes. Therefore, the amount of alpha-fetoprotein released by the fetus is diluted in the larger maternal blood volume. This results in a lower concentration of alpha-fetoprotein in the mother's blood. In contrast, a mother weighing less would have a more concentrated level of MSAFP. However, obese women have a greater increase in body fat with the increased body mass, and therefore the correction for increased body weight might not accurately reflect the true percentage of increased blood volume. The linear formula used to correct MSAFP for maternal weight was evaluated in 50 pound increments. As the mother's weight increased, the rate of abnormally high results increased. Since the MSAFP was overcorrected in heavier women, it is suggested that the linear correction for weight be used only from 100 to 200 pounds. Values obtained from women weighing more than 200 pounds should be corrected as if they weighed 200 pounds only. This would reduce the number of amniocentesis procedures performed by nine percent. (Consumer Summary produced by Reliance Medical Information, Inc.)

Health aspects, Standards, Abnormalities, Physiological aspects, Obesity, Pregnant women, Neural tube, Neural tube defects, Alpha fetoproteins

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Prenatal genetic diagnosis following recurrent early pregnancy loss

Article Abstract:

Over half of the pregnancies lost by women with a history of miscarriages are caused by chromosomal abnormalities. It is not clear whether the chance of a malformation occurring after a lethal type of chromosomal abnormality, particularly a variation in the number of chromosomes, increases in subsequent pregnancies. Furthermore, it is unclear whether the risk of a chromosomal abnormality justifies prenatal diagnostic procedures, which in themselves may be risky. To clarify this issue, couples experiencing two or more miscarriages of unknown cause had their own chromosomes analyzed, as well as those of the fetus. For the study, 305 couples with normal parental chromosomes were selected. Prenatal amniocentesis or chorionic villus sampling was performed in 96 cases. Fetal cells were analyzed using chromosomal karyotyping techniques. The 209 couples declining any prenatal diagnostic procedures were followed up to delivery, at which time abnormal fetuses were karyotyped. Five chromosomal abnormalities were detected (1.6 percent) in the study group. In a group of control pregnancies, three abnormalities were detected by 979 diagnostic procedures (0.3 percent). The number of karyotypes indicating an abnormal number of chromosome (aneuploidy) was higher among couples experiencing recurrent spontaneous pregnancy losses. Therefore, prenatal diagnosis should be offered to couples who have experienced at least two miscarriages. (Consumer Summary produced by Reliance Medical Information, Inc.)

Usage, Diagnosis, Causes of, Genetic screening, Genetic testing, Miscarriage

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