Causes of late fetal death in New Zealand 1980-1999

Background: In recent years there has been an emerging interest in sudden unexplained intrauterine death. Aims: To determine the major causes of late fetal death (LFD) in New Zealand during 1980-1999 and to document the proportion of deaths considered unexplained. In addition, to quantify the number of LFD undergoing post-mortem during this period. Methods: Using the Office for National Statistics (UK) hierarchical classification system, all information available on death certificates was used to assign a single cause to LFD for the period 1980-1999. Trends were analysed using logistic regression and risk factor profiles established for each cause of death. Post-mortem rates and the characteristics of those failing to undergo post-mortem were analysed for the period 1989-1999. Results: LFD rates declined from 60.1 per 10 000 in 1980-1981 to 30.5 in 1998-1999. The declines were not uniform across all causes, with intrapartum deaths declining 73%, congenital anomalies 70% and antepartum asphyxia 50%. In contrast, unspecified deaths increased 1%, and with the decline in other causes of death, also increased proportionally, from 10.8% of LFD in 1980-81 to 28.1% in 1998-1999. Post-mortem rates fell by 3 1% during 1989-1999, with Maori and Pacific babies and those in more deprived New Zealand Deprivation Index areas being significantly less likely to undergo post-mortem. Conclusions: While total LFD rates declined significantly during 1980-1999, rates of unspecified LFD remained static. Low post-mortem rates, however, suggest that many of these deaths may be uninvestigated rather than truly unexplained. Nevertheless, the persistence of a category of death which, to date, has faded to improve with advances in obstetric technology suggests that further measures are necessary if New Zealand's LFD rates are to continue to decline.