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Excerpt
From September 1989 to March 1993, a total of 140 women with singleton pregnancies chose simultaneous placentacentesis/amniocentesis in Gottingen/Northeim (N = 1293) and Oberhausen (N = 112). For successful karyotyping after CVS-SC, usually 15 metaphases (minimum, 5) were analyzed. The number was increased in cases with suspicious or aberrant karyotypes, and Q-banding was performed. A chromosomal mosaic was diagnosed if at least two cells in the CVS-SC preparation were aberrant. One to four amniotic fluid cell cultures were established for chromosomal analysis by the in situ colony technique and/or by the flask method.
In 1329 singleton pregnancies, chromosomal analysis of both chorionic villi after short-time culture (CVS-SC) and amniotic fluid cell cultures (AC) were successful. In the remaining 76 pregnancies, the diagnosis was obtained from either AC or CVS-SC alone: 53 cases could not be provided with a cytogenetic diagnosis from CVS-SC due to the lack of suitable metaphases for reliable cytogenetic diagnosis, nonvillous tissue only, and transportation failure. AC results for confirmation of CVS-SC were lacking in 23 pregnancies, 15 of which were affected by severe oligohydramnios or anhydramnios.
The data of 1329 combined placentacenteses/amniocenteses with successful CVS-SC and AC were recorded. Sampling was performed from the 13th through the 38th week of gestation. The majority of the samples (92.8 percent) were taken during the second trimester. Ninety-five patients (7.2 percent) had sampling beyond the 24th week of gestation, and in 90 percent of these, the indication of karyotyping was the sonographic discovery of a fetal or amniotic fluid abnormality.
Concordant results were obtained in 1218 pregnancies with normal fetal karyotypes, including 46,XY (52.5 percent), 46,XX (46.8 percent), and balanced chromosomal translocations (0.7 percent). An aberrant karyotype, diagnosed after CVS-SC and confirmed by AC, was found in 62 pregnancies.
Discrepant (i. e., false-positive and false-negative) results were obtained in 26 cases (2 percent). Seventeen false-positive results, including 3 nonmosaic and 14 mosaic aberrant karyotypes Table 1 and 9 false-negative findings Table 2 were observed in this series of 1306 pregnancies.
The accuracy, sensitivity, and specificity of second- and third-trimester CVS-SC were calculated from the data of the 1306 pregnancies. Considering the 1280 concordant and 26 discordant results, the accuracy, defined as the proportion of all correct diagnoses, amounts to 98 percent. Based on the 1218 normal concordant and 17 false-positive results, the specificity of CVS-SC (i. e., the proportion of normal karyotypes correctly diagnosed) is calculated to be 98.8 percent.
Among the 1306 cases, nine revealed aberrant karyotypes after AC that had not been detected by CVS-SC Table 2. False-negative findings included trisomy 18 (N = 5), Wolf-Hirschhorn syndrome (N = 1), marker chromosome mosaicism (N = 1), and Turner's syndrome (N = 2).
Of the two pregnancies with a 45,X karyotype in amniocytes, and characteristic ultrasound findings, one showed a male karyotype in CVS-SC, and the other showed a female karyotype with a structural aberrant X-chromosome.
