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 facto r for poor perinatal outcomes. The study objective was to identify risk fac tors associated with short interpregnancy intervals in Denmark. Methods. From a cohort of pregnant women in a geographically defined area i n Denmark (n=11,288) and using register linkage, we identified 5756 multipa rous mothers who completed a detailed interview on social behavior during p regnancy. We restricted our analysis to 2904 mothers who had an interpregna ncy 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 u nplanned pregnancy (OR=2.9, 95% CI: 2.2-3.9), to follow irregular menstruat ion (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, smok ing and low social status were also associated with short interpregnancy in terval Conclusion. Short interpregnancy intervals may be a marker for women at ris k 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 sig nificant role in determining short interpregnancy intervals.