Objective: To assess the value of second trimester genetic ultrasound for screening of Down syndrome conducted at
Srinagarind Hospital, Khon Kaen, Thailand.
Material and Method: The present study sample comprised of 4,033 pregnant women at high risk for fetal chromosomal abnormality, from 17th to 23th week, who had performed second trimester genetic ultrasound before genetic amniocentesis between September 1996 and December 2011. Archived medical records relating to results of genetic ultrasound and genetic amniocentesis were extracted and studied.
Main outcome measure: Sensitivity of genetic ultrasound in the detection of fetal Down syndrome.
Results: There were 3,966 chromosomally normal pregnancies (98.3%), 43 fetuses with Down syndrome (1.1%), and 24 fetuses with other chromosomal abnormality (0.6%). 30 of 43 (69.8%) fetuses with Down syndrome had abnormal genetic
ultrasound. The overall sensitivity of second trimester genetic ultrasound for detecting Down syndrome was 69.8% with a
false-positive rate of 50.4% and likelihood ratio of 1.38. Of all the sonographic markers, short femur, and short humerus
indicated the highest sensitivity at 65.1% and 44.2%. According to likelihood ratio (LR+), chest abnormality, 2 vessel umbilical cord, and facial abnormality, including cleft lip and palate, have highest likelihood ratio (LR+) of 61.49, 46.12, and 46.10, and had sensitivity at 4.7%, 2.3%, and 2.3% respectively.
Conclusion: The sensitivity of second trimester genetic ultrasound for detection of fetal Down syndrome at Srinagarind
Hospital was rather high, and probably is an alternative method of prenatal prediction for high risk pregnant women who refused genetic amniocentesis.

Keywords: Genetic ultrasound, Down syndrome screening, Second trimester