In this retrospective cohort of 165,188 singleton pregnancies and 44,674 multiple-fetal pregnancies in Canada from 1984 to 2000, we compared the incidence of maternal complications. Multiple gestation pregnancies were associated with significant increases in cardiac morbidity, haematologic morbidity, amniotic fluid embolus, pre-eclampsia, gestational diabetes, postpartum haemorrhage, prolonged hospital stay, the need for obstetric intervention, hysterectomy and blood transfusion. Multiple gestation pregnancies are associated with an increased risk of morbidity for the mother. This should be taken into consideration in antenatal care of these women.