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Review
. 2011 Nov 15;157C(4):274-87.
doi: 10.1002/ajmg.c.30321. Epub 2011 Oct 14.

Conjoined twins: a worldwide collaborative epidemiological study of the International Clearinghouse for Birth Defects Surveillance and Research

Osvaldo M Mutchinick  1 , Leonora Luna-Muñoz, Emmanuelle Amar, Marian K Bakker, Maurizio Clementi, Guido Cocchi, Maria da Graça Dutra, Marcia L Feldkamp, Danielle Landau, Emanuele Leoncini, Zhu Li, Brian Lowry, Lisa K Marengo, María-Luisa Martínez-Frías, Pierpaolo Mastroiacovo, Julia Métneki, Margery Morgan, Anna Pierini, Anke Rissman, Annukka Ritvanen, Gioacchino Scarano, Csaba Siffel, Elena Szabova, Jazmín Arteaga-Vázquez
Affiliations
Review

Conjoined twins: a worldwide collaborative epidemiological study of the International Clearinghouse for Birth Defects Surveillance and Research

Osvaldo M Mutchinick et al. Am J Med Genet C Semin Med Genet. .

Abstract

Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. Prevalence has been previously estimated to be 1 in 50,000 to 1 in 100,000 births. The process by which monozygotic twins do not fully separate but form CT is not well understood. The purpose of the present study was to analyze diverse epidemiological aspects of CT, including the different variables listed in the Introduction Section of this issue of the Journal. The study was made possible using the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR) structure. This multicenter worldwide research includes the largest sample of CT ever studied. A total of 383 carefully reviewed sets of CT obtained from 26,138,837 births reported by 21 Clearinghouse Surveillance Programs (SP) were included in the analysis. Total prevalence was 1.47 per 100,000 births (95% CI: 1.32-1.62). Salient findings including an evident variation in prevalence among SPs: a marked variation in the type of pregnancy outcome, a similarity in the proportion of CT types among programs: a significant female predominance in CT: particularly of the thoracopagus type and a significant male predominance in parapagus and parasitic types: significant differences in prevalence by ethnicity and an apparent increasing prevalence trend in South American countries. No genetic, environmental or demographic significant associated factors were identified. Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

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Figures

Figure 1
Figure 1
Total prevalence per 100,000 births (bar) and 95% confidence interval (line) by Surveillance Programs of conjoined twins in 21 Surveillance Programs of the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR).
Figure 2
Figure 2
Prevalence of conjoined twins by 5-year period, 1982–2006 (ICBDSR: Clearinghouse; SAM-ECLAMC: South America-ECLAMC; ICBDSR E/SAM-ECLAMC: Clearinghouse excluding South America-ECLAMC).
Figure 3
Figure 3
Conjoined twins prevalence ratios and 95% CI for maternal age groups relative to the reference group of 25–29 years.
See this image and copyright information in PMC

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