title: Second trimester maternal serum screening using alpha fetoprotein, free beta human chorionic gonadotropin and maternal age specific risk: result of chromosomal abnormalities detected in screen positive for Down syndrome in an Asian population.
abstract: BACKGROUND
  This study was to determine the incidence of chromosome abnormalities in Taiwanese women undergoing prenatal chromosome analysis after a second trimester Down syndrome screening by using maternal age and serum dual-marker testing (alpha-fetoprotein and free-beta unit human chorionic gonadotropin).
  
  
  METHODS
  A total of 10,098 Taiwanese women with pregnancy between 15 and 23 weeks' gestation received second-trimester Down syndrome risk evaluation by dual-marker and maternal age specific risk testing in a single medical center. The study took 22 months. Ninety-seven percent of this study population was less than 34 years old. Ninety-six percent of our cases were screened between 15-20 weeks of gestation. This population was included only after a routine ultrasonography scan for correction of gestational age and exclusion of major structural anomalies. By using an algorithm to detect Down's syndrome, with a risk of 1:270 as a cut-off value, 816 patients were screen-positive for Down syndrome (screen-positive rate 8.0%). Karyotypes were reviewed for 670 (82.1%) mothers who received prenatal karyotype analysis.
  
  
  RESULTS
  Twelve cases of Down syndrome were identified in the screen positive group with an estimated detection rate of 67% (false positive rate 8%). Three cases of Down syndrome were detected in late trimester among the screen-negative group. Seven other fetal chromosome abnormalities were also found among the screen-positive pregnancy. In addition, seven cases were screen-positive for trisomy 18; all of these patients received amniocentesis and only one case was confirmed.
  
  
  CONCLUSIONS
  These findings indicate that this screening program combining alpha-fetoprotein (AFP), free beta human chorionic gonadotropin (free-hCG) and maternal age-specific would achieve a screening efficiency in Taiwanese populations as comparable to those obtained in Caucasian populations. Our results also suggest that approximately 3% of pregnancies with a positive dual marker and maternal age-specific screen results will have a chromosome abnormality despite having a normal routine ultrasound scan. Mothers with positive screening results should be made aware of the implications of a positive result.
mesh_terms: D000328:Adult; D000649:Amniocentesis; D044466:Asian People; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D002869:Chromosome Aberrations / Q000175:diagnosis*; D025063:Chromosome Disorders; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007621:Karyotyping; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011296:Prenatal Diagnosis; D012189:Retrospective Studies; D012307:Risk Factors; D000509:alpha-Fetoproteins / Q000032:analysis*