A comparative, prospective study was in order to diagnose premature aging of placenta and make early diagnosis of perinatal complications. 30 patients were enrolled during the period from march to november 1990 who had unique fetus pregnancy, live fetus, complete membranes, less than 37 weeks gestational age at the beginning of the study. We graded placental maturity by means of ultrasound according to Grannum classification. 22 patients (control group) had Grannum grade III placenta going from 37 to 41 weeks and no perinatal complications for any of them. 8 patients (problem group) showed premature aging of placenta (grade III before 37 weeks) of which 62.5% had perinatal complications (P < 0.05) such as: pregnancy induced hypertension, oligohydramnios and delayed intrauterine growth. With this study it is concluded that premature aging of placenta is associated with high risk pregnancies and lower weight fetus. Observing normal placental maturity for gestational age is associated with good perinatal outcome.