Choice and chance: Determinants of short interpregnancy intervals in Denmark

Background. It is still unclear whether short interpregnancy intervals are a marker for women at risk of poor pregnancy outcome or a direct risk factor for poor perinatal outcomes. The study objective was to identify risk factors associated with short interpregnancy intervals in Denmark. Methods. From a cohort of pregnant women in a geographically defined area in Denmark (n=11,288) and using register linkage, we identified 5756 multiparous mothers who completed a detailed interview on social behavior during pregnancy. We restricted our analysis to 2904 mothers who had an interpregnancy interval of less than 37 months. Multiple logistic regression was used to estimate the Odds Ratio (OR) of having a short interval as a function of a number of determinants. Results. About 4.8% of the mothers had an interpregnancy interval less than 9 months. Short interpregnancy intervals were more likely to occur in an unplanned pregnancy (OR=2.9, 95% CI: 2.2-3.9), to follow irregular menstruation (OR=1.7, 95% CI: 1.1, 2.5) and to occur in older (OR=1.7, 95% CI: 1.1, 2.5) and high parity mothers (OR=1.9, 95% CI: 1.1, 3.1). Poor housing, smoking and low social status were also associated with short interpregnancy interval Conclusion. Short interpregnancy intervals may be a marker for women at risk and these risk factors differ among populations. They also appear to be a result of choice (e.g, in older women). Biological factors also play a significant role in determining short interpregnancy intervals.