BackgroundPregnancy outcomes might be affected by unintended pregnancy such as preeclampsia, preterm birth, cesarean section and low birth weight. The aim of the present study is to assess the association between unintended pregnancy and pregnancy outcomes.MethodsThis was a cross-sectional study conducted in 103 hospitals in Tehran, Iran, in July 2015. The data were collected by trained midwives. The interested independent variable was unintended pregnancy and also preeclampsia, weight gain during pregnancy, preterm birth, cesarean section and low birth weight were considered as interested outcomes, and the association of unintended pregnancy and interested outcomes were assessed.ResultsOut of 5152 cases, 1021 (19.82%) cases were unintended pregnancy. There was no significant relationship between unintended pregnancy and low birth weight (adjusted OR0.67, 95% CI 0.403-1.13, P=0.138), the risk of preterm birth (adjusted OR1.15, 95% CI 0.850-1.57, P=0.351) and preeclampsia (adjusted OR1.21, 95% CI 0.846-1.75, P=0.289). The results of multiple linear regression model showed that the mean difference between two groups was 0.70kg, and weight gain mean in unintended pregnant women significantly was lower than unintended pregnant women (mean difference=0.70, 95% CI 0.14-1.26kg, P=0.014). Multiple logistic regression showed that after adjusting confounders, there was a significant relationship between unintended pregnancy and cesarean section, and the adjusted odds of cesarean section in unintended pregnant women was 1.32 times of intended pregnant women (95% CI 1.07-1.63, P=0.009).ConclusionWe found higher risk of cesarean section and inappropriate weight gain during pregnancy as adverse outcomes of unintended pregnancy in adjusted model.