Seasonality of births and abortions in New South Wales, Australia.

BACKGROUND

Complex seasonal variations in abortions and seasonal trends have been reported worldwide, but there are no data from Australia.

MATERIAL/METHODS: Hospital morbidity and birth data were modelled using time series and regression techniques to describe seasonal changes in births and abortions (1989-99) in NSW, Australia. Data were also analysed to determine demographic predictors of abortions.

RESULTS

A higher proportion of births in NSW were recorded in March and September-October. Irrespective of the nuptiality the lowest seasonal indices were recorded in February and November. For married women aged 20-49 years, voluntary abortions were significantly higher in February (t=0.04) and significantly lower in April (t<0.001) and June (t=0.03) and non-voluntary abortions were significantly higher in February (t=0.002) and March (t=0.006). There was seasonality in voluntary abortions (F=4.3, p<0.001) and no seasonality in non-voluntary abortions (F=2.4, p=0.01) for never married women aged 20-49 years. As similar to married women, voluntary abortions among never married women were significantly higher in February (t<0.001) and significantly low in April (t=0.009). The lowest number of abortions were in April. Non-voluntary abortions occurred mostly in March for married women. The average number of voluntary abortions were significantly higher for never married women than for married women.

CONCLUSIONS

There was a significant seasonality of births and abortions in NSW, Australia, with a peak of conceptions in December/January. Abortions were lowest in April and non-voluntary abortions were peaked in March. These data suggest that the human reproductive behaviour has a close relationship with environmental factors.