Ninety pregnancies conceived by infertile couples using assisted reproductive technologies and 86 pregnancies conceived by infertile couples with routine infertility treatment were analyzed to determine the outcome of and the complications experienced during the pregnancies. Pregnancies ending after 24 weeks' gestation were evaluated for the following complications: pregnancy-induced hypertension, diabetes mellitus, preterm labor, premature rupture of membranes, placenta previa, and fetal growth retardation. A matched control group of normal fertile patients admitted to the obstetric service at Vanderbilt University Medical Center was used to compare the incidence of pregnancy complications among the groups. In the group treated by assisted reproduction, 81 pregnancies were singleton and nine were multiple gestations, whereas in the routine group, 84 were singleton and two were multiple gestations. In the group treated by assisted reproduction, 29 of 90 gestations (32%) ended before 24 weeks, compared with 18 of 86 (21%) in the routine group, a nonsignificant difference. Mean birth weight and gestational age were similar among the three groups for singleton gestations. Among multiple gestations, the mean (± standard error of the mean [SEM]) birth weights were 2513 ± 115, 724 ± 57, and 2282 ± 132 g in the group treated by assisted reproduction, the group receiving routine methods, and the control group, respectively (P<.001 when those treated by routine methods were compared with the other two groups). The mean (± SEM) gestational ages were 36 ± 1.2, 26.5 ± 2.0, and 35.5 ± 1.2 weeks, respectively (P<.01 comparing those treated by routine methods and the other two groups). There were no differences in pregnancy complications for singleton gestations among the three groups. Forty-two of 55 (76%) of those treated by assisted reproduction and 43 of 66 (65%) in the routine group had no complications during the last half of pregnancy. There were no differences in the frequency of late pregnancy complications among the three groups for patients with multiple gestations, although the infants delivered by the patients treated by routine methods were smaller and delivered at an earlier gestational age than those conceived by assisted reproduction or those of controls (P<.01). We conclude that multiple gestations in infertile patients are at high risk for spontaneous abortion and preterm delivery and should be followed closely, whereas singleton gestations appear to have no higher risk for complications than do those of normal fertile controls.