The objective of the study was to explore the association between birth spacing and risk of adverse maternal outcomes. The study was a systematic review of observational studies that examined the relationship between interpregnancy or birth intervals and adverse maternal outcomes. Twenty-two studies met the inclusion criteria. Overall, long interpregnancy intervals, possibly longer than 5 years, are independently associated with an increased risk of preeclampsia. There is emerging evidence that women with long interpregnancy intervals are at increased risk for labor dystocia and that short intervals are associated with increased risks of uterine rupture in women attempting a vaginal birth after previous cesarean delivery and uteroplacental bleeding disorders (placental abruption and placenta previa). Less clear is the association between short intervals and other adverse outcomes such as maternal death and anemia. Long interpregnancy intervals are independently associated with an increased risk of preeclampsia. Both short and long interpregnancy intervals seem to be related to other adverse maternal outcomes, but more research is needed.