A multicenter cohort study was designed to assess pregnancy outcome among natural family planning (NFP) users, and provide the opportunity to address complications in NFP users by planning status and by timing of conception with respect to day of ovulation. There were 877 singleton births in this sample. Complications evaluated were abnormal vaginal bleeding, urinary tract infection, vaginal infection, hypertension of pregnancy, proteinuria, glycosuria, and anemia. There was no significant difference in the mean age, number of prenatal visits or birth weight among optimally and non-optimally timed pregnancies or for planned and unplanned pregnancies. There were higher incidences of 'parity 2 or more' and current smokers in the non-optimally timed pregnancies and lower incidences of prior pregnancy loss and 'currently employed' in the non-optimally timed pregnancies. There was little difference in pregnancy complications with respect to pregnancy timing, with the exception of a significant increased risk of vaginal bleeding late in pregnancy among non-optimally timed conceptions (11.5%) compared to optimally timed pregnancies (5.2%, RR = 2.2, 95% CI 1.3-3.7). More differences were observed in pregnancy complication rates by planning status. Unplanned pregnancies were associated with significantly more late pregnancy bleeding, vaginal infections, proteinuria, glycosuria and medication use than planned pregnancies. Unplanned pregnancies had lower incidences of maternal anemia. Complications of pregnancy were low in this NFP population, irrespective of planned versus unplanned status. Women with planned pregnancies had even fewer complications during pregnancy than women with unplanned conceptions, suggesting that women using NFP to plan their reproduction may be at particularly low risk.