Factors associated with vertical HIV transmission during two different time periods: the impact of zidovudine use on clinical practice at a Brazilian reference centre - Mussi-Pinhata, Marisa Márcia; Kato, Cristina Mikami; Duarte, Geraldo; Paschoini, Marina Carvalho; Bettiol, Heloisa; Quintana, Silvana Maria (International Journal of STD and AIDS, 2003)