A prospective study was carried out to evaluate the significance and efficacy of routine hospital bed rest in prevention of premature birth and pregnancy complications compared to specialized antenatal care at the outpatient clinic of 73 twin pregnancies. The twin pregnancies were screened in health centers by means of symphysis-fundus measurement, and the diagnosis was confirmed by ultrasound examination at the outpatient clinic. On the average the ultrasonic diagnosis was performed during the 23rd gestational week; at this visit the women were divided into two groups with similar follow-up to the end of the 29th gestational week. At this stage one of the groups was hospitalized unless there had been indications for earlier admission. In the hospital group, the mean for gestational week at delivery was 36.7 (+/- 2.4) and in the outpatient group 37.4 (+/- 1.8) respectively (N.S.). There was no difference in the rate of pregnancy complications between the groups too. No statistical differences in the perinatal mortality (7.1% and 1.1% respectively) or birthweights of the newborns were found, either. Present results do not support the idea of using routine hospital bed rest. It could not be proved to have positive effects on the gestational age, birth weight and perinatal mortality of the newborns, nor to the pregnancy complications. In our opinion early diagnosis of twin pregnancy is of decisive importance and specialized ambulatory follow-up could be employed instead of routine bed rest in antenatal care of twin pregnancy.