Interpregnancy interval and preterm birth: correlation versus causation debate continued.

The article presents commentaries on the study by BZ Shachar et al. on the increased odds of preterm birth (PTB) at less than thirty-seven weeks among women with an interpregnancy interval (IPI) of less than six months following a live birth. Topics include reference to comparison of less preterm birth episodes for IPI greater than eighteen months, population-based cohort study design as well as two interpregnancy intervals via maternally matched design concept.