PIP: The most important advancement in perinatology during the past few years has been the possibility to selectively establish a criterion to judge high risk pregnancies, which still represent the great majority of cases of materno-infant morbimortality. Social, economic, and cultural factors, age, biological antecedents of the mother, previous pregnancies, and medical history, have all a great influence in the evaluation of gestation. Through the years several models have been constructed to evaluate high perinatal risks; excluding complications due to danger of congenital abnormalities only 19% of women are exposed to high risk pregnancy. Among prenatal risk factors the most common are toxemia, chronic hypertension, severe cardiopathy, and diabetes; risk factors that may become more evident during delivery or shortly before it are toxemia again, premature rupture of membranes, meconial amniotic fluid, and abnormal presentation.