title: Unusual trend in the prevalence of trisomy 13 in mothers aged 35 and older: A population based study of national congenital anomaly data.
abstract: BACKGROUND
  Trisomy 13 is one of the three autosomal trisomies compatible with viability. It is associated with structural anomalies, learning disability and poor survival. Advanced maternal age is the most frequently suggested risk factor. This is a population based register study to investigate the temporal trends of trisomy 13.
  
  
  METHODS
  Chromosomal trisomies were reviewed by the Welsh Congenital Anomaly Register using data from 1998-2012. All pregnancy outcomes were included. Prevalence rates and trends for all cases and for cases with mothers aged below 35 years and those aged 35 years and older were plotted for trisomy 13, 18 and 21. Possible risk factors contributing to the trend in older mothers were compared in the early and late period of the study.
  
  
  RESULTS
  There were 124 cases of trisomy 13 over the 15 year period with 55 mothers aged 35 years and older. Overall prevalence was 2.5 per 10,000 total births. A significant declining trend in the prevalence of trisomy 13 in mothers aged 35 and older (χ(2) trend = 4.98, p=0.026) was noted. Rates for younger mothers were lower and remained stable. Prevalence of trisomy 18 and 21 in older mothers remained stable.
  
  
  CONCLUSIONS
  The unexpected declining trend in trisomy 13 in older mothers could not be explained by the risk factors examined in this study. There have been no other reports of trends in the prevalence of trisomy 13 in older mothers in recent years. There is further need for surveillance of trends in future and in other populations.
authors.affiliation: Congenital Anomaly Register and Information Service for Wales (CARIS), Singleton Hospital, Swansea, United Kingdom.
authors.forename: Deepa Balachandran
authors.initials: DB
authors.lastname: Nair
authors.affiliation: Congenital Anomaly Register and Information Service for Wales (CARIS), Singleton Hospital, Swansea, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Tucker
authors.affiliation: Congenital Anomaly Register and Information Service for Wales (CARIS), Singleton Hospital, Swansea, United Kingdom.
authors.forename: Rhian
authors.initials: R
authors.lastname: Hughes
authors.affiliation: Congenital Anomaly Register and Information Service for Wales (CARIS), Singleton Hospital, Swansea, United Kingdom.
authors.forename: Judith
authors.initials: J
authors.lastname: Greenacre
authors.affiliation: Congenital Anomaly Register and Information Service for Wales (CARIS), Singleton Hospital, Swansea, United Kingdom.
authors.forename: Margery
authors.initials: M
authors.lastname: Morgan
mesh_terms: D000328:Adult; D025063:Chromosome Disorders / Q000453:epidemiology*; D002882:Chromosomes, Human, Pair 13; D005260:Female; D006801:Humans; D008423:Maternal Age; D011159:Population Surveillance; D011247:Pregnancy; D015995:Prevalence; D014314:Trisomy; D000073839:Trisomy 13 Syndrome; D014852:Wales / Q000453:epidemiology
keywords: Patau syndrome; advanced maternal age; prevalence rates; trends; trisomy 13