Cloacal exstrophy and related abdominal wall defects in Manitoba: incidence and demographic factors.

A retrospective descriptive study of omphalocele and exstrophic defects of the abdominal wall was carried out in Manitoba to determine the prevalence of these defects, changes in birth incidence with time and their etiologic heterogeneity. The incidence of isolated omphalocele was similar to that reported in other series but the overall incidence of other types of abdominal wall defects was high. Cloacal exstrophy, bladder exstrophy and amnion disruption defects contributed significantly to the number of cases ascertained and emphasized the heterogeneity of abdominal wall defects. There were fluctuations in birth incidence with time with cloacal exstrophy especially apparently being more common in 1980-81. No specific demographic or environmental factors were documented in the cases seen in 1980-81 which could explain the high incidence in these years. Cloacal exstrophy is, however, now appreciated to be much more common than first realized. Studied directed at elucidation of the causes of apparent changes in incidence of malformations such as omphalocele or exstrophic defects will have to take into account both the fluctuations in background incidence of these defects and the considerable diversity in their etiology.