History and Objectives: Due to importance of preterm labor problems and its complications and regarding the controversies on the relationship of interpregnancy intervals of less than 15 months and preterm labor and in order to define effect of interpregnancy interval of less than 15 months on preterm labor, the present study was performed at Shabihkhani Maternity hospital during 1997-1998.

Materials and Methods: In a case study, control group (N=100) consisted labors after 37 weeks of pregnancies and a case group (N=70) of labors before 37 weeks of pregnancy. Interpregnancy interval of less than 15 months in two groups after termination of preceding pregnancy and start of next pregnancy was evaluated. Case and control groups were matched for influencing factors on preterm labor. Chi-square statistical analysis was used to test the results and Odd’s ratio were determined.

Results: No significant differences were observed among case and control groups (N=100). Short interpregnancy interval was 9% and 21.4% among case and control group respectively (P<0.02). Preterm labor was 2.7 times higher among women with interpregnancy interval of less than 15 month.

Conclusion: Interpregnancy interval of less than 15 months has an effect on incidence of preterm labor. Further research in required pinpointing the factors involved with the short interpregnancy interval.