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Korean Journal of Obstetrics & Gynecology 2004;47(8):1474-1481.
Published online August 1, 2004.
Ultrasound Screening for Fetal Down Syndrome in the Second Trimester of Pregnancy.
Myoung Jin Moon, Hyun Mee Ryu, Jin Hoon Chung, Ha Jung Lim, June Seek Choi, Joo Oh Kim, Joong Sik Shin, Hyun Kyong Ahn, Jung Yul Han, Moon Young Kim, Jae Hyug Yang, Kyu Hong Choi, Mi Jin Song, Jeong Yeon Cho, Young Ho Lee
1Department of Obstetrics and Gynecology, Samsung Cheil Hospital and Women's Healthcare Center, Sungkyunkwan University, School of Medicine, Seoul, Korea.
2Department of Diagnostic Radiology, Samsung Cheil Hospital and Women's Healthcare Center, Sungkyunkwan University, School of Medicine, Seoul, Korea.
To determine the risk of Down syndrome in fetuses with sonographic markers using the likelihood ratios and individual risk assessment. METHODS: We retrospectively evaluated the midtrimester genetic sonographic features of fetuses with Down syndrome and compared them with euploid fetuses. Patients were referred for an increased risk of aneuploidy and evaluated for the presence of structural defects, a nuchal fold, short long bones, pyelectasis, brachycephaly, small stomach, and hyperechoic bowel. Outcome information included the results of genetic amniocentesis (if performed), the results of pediatric assessment, and follow-up after birth. The sensitivity, specificity, and likelihood ratios for markers ware calculated isolated findings. RESULTS: There were 59 fetuses with Down syndrome and 600 euploid fetuses. The presence of any marker resulted in sensitivity for the detection of Down syndrome of 86.4% with a false-positive rate of 13.6%. Structural defect had a likelihood ratio of 77.8. As an isolated marker, the nuchal fold, short humerus, short femur, echogenic bowel and renal pyelectasia has a likelihood ratio of 20.2, 12.7, 3.9, 2.5, 1.1 respectively. Other isolated markers had low likelihood ratios because of the higher prevalence in the unaffected population. CONCLUSION: Combining second-trimester serum testing and fetal sonography is a feasible approach to Down syndrome screening, compatible with current obstetric practice. Although an isolated marker with a low likelihood ratio may not increase a patient's risk of Down syndrome, the presence of such a marker precludes reducing the risk of aneuploidy. This information will be useful in counseling pregnant women who are at high risk for fetal Down syndrome and who prefer to undergo genetic sonography before deciding about genetic amniocentesis.
Key Words: Isolated likelihood ratio, Genetic sonogram, Down syndrome, Prenatal diagnosis

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