title: A population-based study of prevalence of Down syndrome in Southern Thailand.
abstract: BACKGROUND
  Down syndrome (DS) is the most common chromosomal disorder that causes mental retardation. In 2009, a population-based birth defects study was implemented in three provinces in southern Thailand. This study aimed to determine the prevalence of DS in the studied regions, and the proportion of DS fetuses detected by prenatal screening.
  
  
  METHODS
  Data were obtained from a population-based surveillance study undertaken during 2009-2013. Entries in the birth defects registry included live births, stillbirths after 24 weeks gestational age, and terminations of pregnancy following prenatal diagnosis. Infants with clinical characteristics of DS had a chromosomal study to make a definite diagnosis.
  
  
  RESULTS
  Of the total 186 393 births recorded during the study period, 226 DS cases were listed, giving a prevalence of 1.21 per 1000 births [95% confidence interval (CI) 1.05-1.37]. The median maternal age was 36.5 years with a percentage of maternal age ≥35 years of 60.6%. Seventy-seven cases (34.1% of all cases) were diagnosed prenatally and these pregnancies were terminated. The prevalence of DS per 1000 births was significantly higher in older women, from 0.47 (95% CI 0.28-0.67) in mothers aged <30 years to 0.88 (95% CI 0.59-1.17) in mothers 30-<35 years (P<0.01), and to 4.74 (95% CI 3.95-5.53) in mothers ≥35 years (P<0.001).
  
  
  CONCLUSIONS
  The prevalence of DS significantly increased with maternal age. About 35% of DS cases were detected prenatally and later terminated. Hence, examining only registry live births will result in an inaccurate prevalence rate of DS.
authors.affiliation: Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, 90110, Thailand. somchit.j@psu.ac.th.|Department of Pediatrics, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, 90110, Thailand. somchit.j@psu.ac.th.
authors.forename: Somchit
authors.initials: S
authors.lastname: Jaruratanasirikul
authors.affiliation: Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, 90110, Thailand.
authors.forename: Ounjai
authors.initials: O
authors.lastname: Kor-Anantakul
authors.affiliation: Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, 90110, Thailand.
authors.forename: Montira
authors.initials: M
authors.lastname: Chowvichian
authors.affiliation: Medical Education Center Songkhla Hospital, Songkhla, Thailand.
authors.forename: Wannee
authors.initials: W
authors.lastname: Limpitikul
authors.affiliation: Medical Education Center Hatyai Hospital, Songkhla, Thailand.
authors.forename: Pathikan
authors.initials: P
authors.lastname: Dissaneevate
authors.affiliation: Medical Education Center Trang Hospital, Songkhla, Thailand.
authors.forename: Nitthakarn
authors.initials: N
authors.lastname: Intharasangkanawin
authors.affiliation: Phatthalung Hospital, Songkhla, Thailand.
authors.forename: Atchara
authors.initials: A
authors.lastname: Sattapanyo
authors.affiliation: Phatthalung Hospital, Songkhla, Thailand.
authors.forename: Sermsri
authors.initials: S
authors.lastname: Pathompanitrat
authors.affiliation: Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, 90110, Thailand.
authors.forename: H
authors.initials: H
authors.lastname: Sriplung
mesh_terms: D000032:Abortion, Therapeutic / Q000706:statistics & numerical data*; D000328:Adult; D016001:Confidence Intervals; D004314:Down Syndrome / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D015995:Prevalence; D012042:Registries; D012189:Retrospective Studies; D013785:Thailand / Q000453:epidemiology
keywords: Down syndrome; birth defect registry; prenatal screening; termination of pregnancy; trisomy 21