According to Websters Encyclopedic Unabridged Dictionary of the English Language, viable of a fetus it means having reached such a stage of development as to be capable of living, under normal conditions, outside the uterus. Viability exists as a function of biomedical and technological capacities, which are different in different parts of the world. As a consequence, there is, at the present time, no worldwide, uniform gestational age that defines viability. Viability is not an intrinsic property of the fetus because viability should be understood in terms of both biological and technological factors. It is only in virtue of both factors that a viable fetus can exist ex utero and thus later achieve independent moral status. Moreover, these two factors do not exist as a function of the autonomy of the pregnant woman. When a fetus is viable, that is, when it is of sufficient maturity so that it can survive into the neonatal period and later achieve independent moral status given the availability of the requisite technological support, and when it is presented to the physician, the fetus is a patient. In the United States viability presently occurs at approximately 24 weeks of gestational age (Chervenak, L.B. McCullough; Textbook of Perinatal Medicine, 1998). In Portugal, the mortality increase significantly with GA<25 weeks. At 25 weeks mortality was 44.4% and at 26 weeks was 24.4% (I. Macedo et al. Matemidade Dr. Alfredo da Costa, Lisbon, 2000). In Poland during last years we observe also a very significant decrease of perinatal mortality. There are several aspects of fetal viability: ethical, social, psychological and medical. Ethical aspects There is a compelling conceptual and clinical reason to reject Primum non nocere as the primary principle of perinatal ethics; virtually all medical interventions involve unavoidable risks of harm, for example, amniocentesis. If Primum non nocere were to be made the primary principle of perinatal ethics, virtually all of perinatal medicine would be unethical. Social aspects Greatly increased advances in perinatal medicine lead on one hand to a high quality of care expected and demanded by both the health care professionals and patients, but on the other hand the resources available for responding to the expectations and demands are becoming increasingly stretched. Even in the high-income countries, the available resources are scarce in relation to these demands a high quality of care expected and demanded by both the health care professionals and patients, but on the other hand the resources available for responding to the expectations and demands are becoming increasingly stretched. Medical aspects During the preconceptional period the most important actions are: family planning, education, analysis of previous obstetrical miscarriages and prevention of congenital malformations (folic acid). Pregnancy presents several problems, which can significantly influence fetal viability. Proper management of these problems can improve perinatal outcome. Among others prevention of prematurity is the most important goal of contemporary perinatal medicine. Enhancement of fetal viability There are several possibilities to enhance fetal viability. The most important are: organization of perinatal care, introduction of new technologies to perinatal medicine, intensive fetal therapy and early detection of fetal distress. Three levels system of perinatal care, transport in utero, introduction and promotion of new methods, continues education of staff are characteristic for the modern organization of perinatal medicine. Echocardiography, Color Doppler Energy, 3D sonography, prenatal diagnosis (cordocentesis, analysis of fetal cells in maternal blood,.), fetal pulse oximetry, mathematical analysis of the signal are the methods which should be used at the highest level of perinatal care. Today, the prospect of survival is only about 1 in 10 at 23 weeks, and if the child lives it is more likely to be handicapped that not. At 24 weeks the chance of a normal survivor is about 50%, and after this the odds are in favor of a normal survivor. Considering this data, intensive care should be an optional choice for fetuses at 23 and 24 weeks of gestation and should be offered to every fetus at 25 weeks or more.