A POPULATION-BASED STUDY OF ABDOMINAL-WALL DEFECTS IN SOUTH-AUSTRALIAAND WESTERN-AUSTRALIA

The purpose of this study was to determine the prevalence, clinical ch aracteristics, prenatal diagnosis and occurrence of other birth defect s with abdominal wall defects in births and terminations of pregnancy in South Australia (SA) and Western Australia (WA) over the period 198 0-90. Cases of gastroschisis, exomphalos, bladder exstrophy, cloacal e xstrophy and body stalk anomaly were ascertained from the WA Birth Def ects Registry (1980-90) and the SA Birth Defects Register (1986-90). T he registers are comparable population-based data collections with inf ormation on livebirths and stillbirths of at least 400 g birthweight o r 20 weeks' gestation, and terminations of pregnancy for fetal abnorma lity. The prevalence of gastroschisis was 1.65/10 000 births (59 cases ) and of exomphalos 2.90/10000 births (104 cases). There was no signif icant difference in prevalence of exomphalos or gastroschisis between SA and WA for the years 1986-90. However, if data from WA for the year s 1980-85 were included, SA had a significantly higher prevalence of e xomphalos (prevalence ratio 1.71, confidence interval [CI] 1.16-2.55), although not of gastroschisis (prevalence ratio 1.35, CI 0.79-2.32). Exomphalos was significantly more common in mothers < 20 years (odds r atio [ORI 2.45, CI 1.22-4.86) and in mothers of 40 years or older (OR 5.65, CI 1.69-16.77). Gastroschisis was more common in younger mothers (OR 8.76, CI 4.02-19.32). Both exomphalos and gastroschisis were asso ciated with low birthweight, prematurity, intrauterine growth retardat ion and caesarean section. The reason for the higher prevalence of exo mphalos in SA than WA was not clear, but may be related to differences in prenatal diagnosis. The association between maternal age < 20 year s and exomphalos raises the possibility of common factors in the aetio logy of gastroschisis and exomphalos.