The prevalence of anencephalus and spina bifida in New Zealand.

Despite the plethora of epidemiological research conducted on anencephalus and spina bifida, few of the studies have used multiple source case ascertainment and controlled for the effect of possible confounding factors. This paper reports the results from a study of the relationships between various risk factors and the prevalence of anencephalus and spina bifida in New Zealand during 1978-82, using case data obtained from multiple sources and a national cohort of births as the denominator. The rates of anencephalus and spina bifida in New Zealand were 0.78/1000 and 0.94/1000 total births, respectively. The rate of a neural tube defect (NTD) birth for Maori parents was less than for their non-Maori counterparts. Paternal ethnic origin and maternal ethnic origin made similar contributions to the model of anencephalus rates, but the results suggest that paternal ethnic origin is a less important risk factor in the prevalence of spina bifida. The rate of both NTD was high among female infants and low among births to women born in countries other than the British Isles and New Zealand. The rate of anencephalus showed a distinct north-south gradient, but there was no evidence of effects for maternal or paternal age, parity, urban-rural place of residence, nuptiality, social class or season of birth in the prevalence of either NTD in New Zealand.