Objective: The aim of the study was to assess optimal time to conceive after previous delivery associated with smallest risk of preterm birth.
Methods: We selected all women (n = 2723) with their first and second singleton delivery between the years 2004 and 2012. Inter-pregnancy interval was defined as that between live birth and subsequent conception. We performed logistic regression analyses to assess the risk of preterm birth adjusted for maternal age and body mass index.
Results: Association between inter-pregnancy interval and the natural logarithm of the adjusted relative risk of preterm birth had a J-shaped curve with lowest risk at 15 months after last birth.
Conclusion: The optimal time to conceive after a previous delivery is 15 months, as longer or shorter interval are associated with increased risk of preterm birth. Women with short or long inter-pregnancy intervals were 1.6 times more likely to experience preterm birth.
Keywords: Inter-pregnancy interval; preterm delivery; risk factors.