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.