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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. (C) 2011 Wiley Periodicals, Inc.

This study describes the epidemiology of congenital amelia (absence of limb/s), using the largest series of cases known to date. Data were gathered by 20 surveillance programs on congenital anomalies, all International Clearinghouse for Birth Defects Surveillance and Research members, from all continents but Africa, from 1968 to 2006, depending on the program. Reported clinical information on cases was thoroughly reviewed to identify those strictly meeting the definition of amelia. Those with amniotic bands or limb-body wall complex were excluded. The primary epidemiological analyses focused on isolated cases and those with multiple congenital anomalies (MCA). A total of 326 amelia cases were ascertained among 23,110,591 live births, stillbirths and (for some programs) elective terminations of pregnancy for fetal anomalies. The overall total prevalence was 1.41 per 100,000 (95% confidence interval: 1.26-1.57). Only China Beijing and Mexico RYVEMCE had total prevalences, which were significantly higher than this overall total prevalence. Some under-registration could influence the total prevalence in some programs. Liveborn cases represented 54.6% of total. Among monomelic cases (representing 65.2% of nonsyndromic amelia cases), both sides were equally involved, and the upper limbs (53.9%) were slightly more frequently affected. One of the most interesting findings was a higher prevalence of amelia among offspring of mothers younger than 20 years. Sixty-nine percent of the cases had MCA or syndromes. The most frequent defects associated with amelia were other types of musculoskeletal defects, intestinal, some renal and genital defects, oral clefts, defects of cardiac septa, and anencephaly. (C) 2011 Wiley Periodicals, Inc.

BACKGROUND: Holoprosencephaly (HPE) is a developmental field defect of the brain that results in incomplete separation of the cerebral hemispheres that includes less severe phenotypes, such as arhinencephaly and single median rnaxillary central incisor. Information on the epidemiology of HPE is limited, both because few population-based studies have been reported, and because small Studies must observe a greater number of years in order to accumulate sufficient numbers of births for a reliable estimate. METHODS: We collected data from 2000 through 2004 from 24 of the 46 Birth Defects Registry Members of the International Clearinghouse for Birth Defects Surveillance and Research. This Study is based on more than 7 million births in various areas from North and South America, Europe, and Australia. RESULTS: A total of 963 HPE cases were registered, yielding an overall prevalence of 1.31 per 10,000 births. Because the estimate was heterogeneous, possible causes of variations among populations were analyzed: random variation, Under-reporting and over-reporting bias, variation in proportion of termination of pregnancies among all registered cases and real differences among populations. CONCLUSIONS: The data do not suggest large differences in total prevalence of HPE among the studied Populations that would be useful to generate etiological hypotheses.