Abstract Objective To compare the obstetric characteristics of twin pregnancies conceived by in vitro fertilization (IVF) and ovulation induction with those conceived spontaneously. Design Case control study. Setting: Tertiary Medical Center. Patients: All twin deliveries that were achieved by IVF ( n = 558) and ovulation induction ( n = 478) from January 1988 through December 2002 were evaluated. Each group was compared with a control group that conceived spontaneously ( n = 3694) and was delivered during the same period. Interventions: Ovulation induction, IVF-ET. Main outcome measures: Obstetrical complications. Results Multivariate analysis showed that patients who conceived with the assistance of IVF and ovulation induction had a significantly higher risk for gestational diabetes mellitus (odds ratio OR = 2.41, 95% confidence interval CI = 1.77–3.29 and OR = 1.71, CI = 1.2–2.42, respectively), cesarean section (OR = 2.17, 95% CI = 1.74–2.70 and OR = 1.76, CI = 1.43–2.16, respectively), and a lower gestational age at birth in the IVF group (OR = 0.91, 95% CI = 0.88–0.94), compared with their controls. Conclusions After controlling for maternal age, and nulliparity we demonstrated that twin pregnancies conceived with the assistance of IVF and ovulation induction are at increased risk for gestational diabetes mellitus, and delivery by cesarean section. In addition, IVF conceived pregnancies have a lower gestational age at birth.