[Amniotic chromosomal analysis in pregnant women identified by triple-marker testing as screen positive.].
BACKGROUND
Maternal serum triple marker screening (alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol) can detect 60-70% of Down syndrome and 60% of Edwards syndrome. Previous studies have reported that positive serum screening is related to other fetal chromosomal abnormalities, pregnancy complications, and adverse outcomes. We determined the incidence and karyotype of chromosomal abnormalities in screen positive women and evaluated a relationship between chromosomal and ultrasonographic abnormalities.


METHODS
Of the 49,806 pregnant women between 15 and 23 weeks' gestational age who received prenatal serum screening with a cut-off value (a risk of 1:270 for Down and 1:100 for Edwards syndrome), 2,116 (4.2%) and 196 (0.4%) were screen positive for Down syndrome and for Edwards syndrome, respectively. Chromosomal analysis in amniotic fluid was performed for 1,893 (89.5%) of the Down positive and 140 (71.4%) of the Edwards positive pregnant women. Ultrasonographic examination was performed to detect fetal abnormalities.


RESULTS
Eighty-three cases of chromosomal abnormalities including 40 trisomy 21 (2.1%) and 43 other chromosomal abnormalities (2.3%) were identified in the Down screen positive. Other chromosomal abnormalities included 9 numerical and 34 structural abnormalities. Ten cases of chromosomal abnormalities (9 trisomy 18 and 1 trisomy 9) were detected in the Edwards screen positive. Ultrasonographic abnormalities were found more frequently in the women who had chromosomal aberrations.


CONCLUSIONS
These data suggest that 4.4% of the Down screen and 7.1% of the Edwards screen positive pregnancy have fetal chromosomal abnormalities. Positive Down screening results reflect a relatively high probability of other abnormalities except trisomy 21. Edwards screen positive group show a low frequency of other chromosomal abnormalities except trisomy 18. A simultaneous use of maternal serum screening and ultrasonograms could be useful for the diagnosis of fetal abnormalities.