In Catalonia, ultrasonographic control of pregnancies is carried out in hospitals and in certain primary care centers within the women's care program. There is no scientific evidence on its efficacy in the improvement of the fetal viability at this level of care; therefore, the question of whether obstetric ultrasonography is efficacious and safe in primary care cannot be answered properly to recommend its application. However, it may be assessed whether routine ultrasonography, the one expected to be carried away in primary care centers, is more effective than selective ultrasonography, i.e., the one carried away in the referential gynecology and obstetrics service due to risk conditions during the pregnancy.