ObjectivesTo evaluate implementation of 1994 United States Public Health Service guidelines for zidovudine (ZDV) use in HIV-infected women and their newborns by describing the prevalence of use of perinatal ZDV and other antiretrovirals and by investigating determinants of not receiving perinatal ZDV.Design/MethodsThe Perinatal AIDS Collaborative Transmission Study is a prospective cohort study designed to collect information related to mother-to-child HIV transmission that was conducted in New York City (NY), Newark (NJ), Baltimore (MD), and Atlanta (GA), U.S.A. The current analysis was restricted to infants born between July 1994 and June 1998.ResultsUtilization rates for antenatal, intrapartum, and neonatal ZDV increased from 41% to 70% during the 4-year period. Use of combination antiretrovirals increased from fewer than 2% of women in 1994 to 1995 to 35% in 1997 to 1998. Antenatal and neonatal ZDV use increased each year, but intrapartum ZDV use reached a plateau after 1996. Mother-infant pairs with the following characteristics were less likely to have received a complete 3-part ZDV regimen: older maternal age, CD4 count >500 cells/&mgr;l, preterm birth, cocaine or heroin use during pregnancy, positive newborn drug screen test result, and smoking or alcohol use during pregnancy. By multivariate logistic regression adjusted for hospital and year of birth, cocaine or heroin use during pregnancy (odds ratio [OR], 2.3; 95% confidence interval [CI], 1.6–3.3), maternal CD4 count (OR, 0.4; 95% CI, 0.2–0.8; comparing <200 with >500 cells/&mgr;l), and preterm birth (OR, 1.6; 95% CI, 1.1–2.5) remained independently associated with not receiving the complete ZDV regimen.ConclusionsZDV use by pregnant HIV-infected women and their infants has increased dramatically since publication of the 1994 guidelines. Nevertheless, women who abuse substances, give birth preterm, or have less advanced immunosuppression, were at substantial risk of not receiving the complete ZDV regimen.