The Plunket National Child Health Study: birth defects and sociodemographic factors

The Plunket National Child Health Study was set up to examine the health experience of a representative sample of New Zealand children. This paper examines the association of birth defects with the sociodemographic variables of maternal age and education, parity, socioeconomic group, region of domicile and marital status; infant's ethnic group and sex. The effect of maternal smoking on the prevalence of birth defects was also examined. The paper compares the prevalence of birth defects in infants alive at 6 weeks with the reported prevalence at birth as described in various other publications.

A cohort of 4286 children born in New Zealand during 1990-1 were enrolled in the study. The presence of birth defects in the study population was determined by clinical examination and review of hospital or midwife referrals. All described defects were reviewed and coded according to the ICD-9.

The overall prevalence of birth defects in the study was 4.3%. There was a significant association between socioeconomic status and the incidence of birth defect but no other significant sociodemographic variations. Cigarette smoking had no statistically significant effect on the rate of birth defects. There was a marked difference between the rates for certain defects in the Plunket study when compared to Health Department notifications.

Because of the differences between the current study and official Health Department notifications we suggest that criteria for congenital anomaly notification are clarified, and that a second notification takes place at six weeks of age.