Indication-specific accuracy of second-trimester genetic ultrasonography for the detection of trisomy 21.
OBJECTIVE
The object of this study was to determine whether there are any clinically significant indication-specific variations in the accuracy of second-trimester genetic ultrasonography and to provide a risk adjustment for fetal trisomy 21 according to the results of genetic ultrasonography.


METHODS
From November 1, 1992, to September 30, 1998, a second-trimester genetic sonogram was offered to all pregnant women who were at an increased risk for fetal trisomy 21 (>/=1:274) because of either advanced maternal age (>/=35 years) or abnormal serum biochemical profile or both of these. Outcome information included the results of genetic amniocentesis if performed and the results of pediatric assessment and follow-up after birth. In determining diagnostic accuracy of the genetic sonogram the presence of >/=1 abnormal ultrasonographic marker was considered an abnormal test result.


RESULTS
A total of 1835 fetuses with known outcomes underwent genetic ultrasonography between 15 and 24 weeks' gestation; of these 1792 had normal results, 34 had trisomy 21, and 9 had other chromosomal abnormalities. The likelihood of fetal trisomy 21 was reduced by 80% after a normal result of genetic ultrasonography. The overall sensitivity, specificity, and positive and negative predictive values of genetic ultrasonography for the detection of trisomy 21 were 82%, 91%, 15%, and 99.6%, respectively. There were no significant indication-specific variations in the accuracy of second-trimester ultrasonography. The sensitivity for the detection of fetal trisomy 21 ranged from 80% among women with advanced maternal age to 100% among women with both an abnormal biochemical profile and advanced maternal age.


CONCLUSIONS
The likelihood of fetal trisomy 21 risk was reduced 80% after a normal result of genetic ultrasonography. In addition there were no significant indication-specific variations in the detection rate of genetic ultrasonography.
Vintzileos
A M
AM
Division of Maternal-Fetal Medicine, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School/St Peter's University Hospital, New Brunswick, USA.
Guzman
E R
ER
Smulian
J C
JC
Day-Salvatore
D L
DL
Knuppel
R A
RA
D000293:Adolescent; D000328:Adult; D000649:Amniocentesis; D002869:Chromosome Aberrations / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000235:genetics; D025063:Chromosome Disorders; D004314:Down Syndrome / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D005820:Genetic Testing; D005865:Gestational Age; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D016017:Odds Ratio; D010865:Pilot Projects; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000097:blood / Q000235:genetics*; D018566:Pregnancy, High-Risk; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal