Distribution of serum levels of alphafetoprotein, beta subunit of human chorionic gonadotropin and unconjugated estriol between 14 and 19 weeks of pregnancy in normal gestations in the city of Ribeirão Preto, São Paulo, Brazil - Patta, Maristela Carbol; Duarte, Geraldo; Pina Neto, João Monteiro de; Machado, J. C.; Cunha, Sérgio Pereira da; Berezowski, Aderson Tadeu (World Congress of Ginecological Endocrinology, 2000)