title: The use of second-trimester genetic sonogram in guiding clinical management of patients at increased risk for fetal trisomy 21.
abstract: OBJECTIVE
  To test the efficacy of ultrasound in detecting fetuses with trisomy 21.
  
  
  METHODS
  From November 1, 1992, to December 31, 1995, a second-trimester genetic sonogram was offered to all women with singleton fetuses at increased risk (at least 1:274) for trisomy 21, who had either declined genetic amniocentesis or chose to have a sonogram before deciding whether to undergo an amniocentesis. In addition to standard fetal biometry, the following ultrasound markers for aneuploidy were evaluated: structural anomalies (including face, hands, and cardiac [four-chamber view and outflow tracts]), short femur, short humerus, pyelectasis, nuchal fold thickening, echogenic bowel, choroid plexus cysts, hypoplastic middle phalanx of the fifth digit, wide space between the first and second toes, and two-vessel umbilical cord. Outcome information included the results of genetic amniocentesis, if performed, or the results of postnatal pediatric assessment and follow-up.
  
  
  RESULTS
  Five hundred seventy-three patients had a genetic sonogram between 15 and 23 weeks' gestation: 378 patients had advanced maternal age (at least 35 years), 141 had abnormal serum biochemistry, and 54 had both. The majority (495, or 86.3%) had a normal genetic sonogram (absence of abnormal ultrasound markers); 51 (9%) had one marker present, and 27 (4.7%) had two or more markers present. Outcome was obtained on 422 patients (the remaining were ongoing pregnancies or were lost to follow-up). Twelve of 14 fetuses with trisomy 21, one fetus with trisomy 13, and one fetus with triploidy had two or more abnormal ultrasound markers present; one fetus with trisomy 21 had one abnormal marker and one had a completely normal ultrasound. When one or more abnormal ultrasound markers were present, the sensitivity, specificity, and positive and negative predictive values for trisomy 21 were 92.8%, 86.7%, 19.4%, and 99.7%, respectively. When two or more abnormal ultrasound markers were present, the corresponding values were 85.7%, 96.8%, 48%, and 99.5%. In the study population, the amniocentesis rate was 12.7% overall and 17.3% in cases with known outcome.
  
  
  CONCLUSIONS
  Second-trimester genetic sonogram may be a reasonable alternative for patients at increased risk for fetal trisomy 21 who wish to avoid amniocentesis. In experienced hands, this approach may result in a high detection rate of trisomy 21 (93%), with an amniocentesis rate of less than 20%.
authors.affiliation: Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School/St. Peter's Medical Center, New Brunswick, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Vintzileos
authors.forename: W A
authors.initials: WA
authors.lastname: Campbell
authors.forename: J F
authors.initials: JF
authors.lastname: Rodis
authors.forename: E R
authors.initials: ER
authors.lastname: Guzman
authors.forename: J C
authors.initials: JC
authors.lastname: Smulian
authors.forename: R A
authors.initials: RA
authors.lastname: Knuppel
mesh_terms: D000328:Adult; D000649:Amniocentesis; D000013:Congenital Abnormalities / Q000000981:diagnostic imaging; D004314:Down Syndrome / Q000000981:diagnostic imaging*; D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging; D006801:Humans; D008423:Maternal Age; D011237:Predictive Value of Tests; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D018566:Pregnancy, High-Risk; D011446:Prospective Studies; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal