The effect of maternal age and birth weight on the temporal trend in stillbirth rate in Austria during 1984-1993.

We assessed the risk of stillbirth in Austria during 1984-1993 in dependence of the variables maternal age, birth weight, year of birth and sex. All children born in Austria between 1984 and 1993 were included in the study (905,939 births). The risk of stillbirth was estimated by means of a logistic regression model. During the study period, stillbirths decreased significantly in Austria. Both birth weight and maternal age had a non-linear association with the risk of stillbirth. The lowest stillbirth rate was in the birth weight category of 3300-3899 grams (g). Of all stillbirths 62% occurred in infants weighing < or = 2500 g at birth. We also found a significant interaction between birth weight and year of birth suggesting that the effect of birth weight was not stable over the years. The proportion of young mothers (< 20 years) decreased clearly over the observation period. The proportion of low birth weight (< = or 2500 g) infants remained around 7.5% during the 10-year period, but the stillbirth rate decreased linearly over time in this group. In infants weighing > 2500 g at birth the stillbirth risk decreased during first five years but started to increase thereafter. Since over 60% of stillbirths in Austria occur in the low birth weight category, it is obvious that more effective strategies are needed for prevention of low birth weight births and fetal immaturity. In addition, further efforts are needed to prevent also high birth weight of newborns particularly in diabetic mothers.