OBJECTIVE: Rates of vertical HIV transmission between mother and child are low, allowing many HIV positive women to have children with near impunity. In this study, data from the Swiss Mother and Child HIV Cohort Study were used to describe maternal characteristics and their association with pregnancy outcomes in HIV positive women. STUDY DESIGN: HIV positive women were followed prospectively during their pregnancies and deliveries by anonymous questionnaires between January 2003 and October 2008. Adverse pregnancy outcomes included preterm delivery, preeclampsia and gestational diabetes mellitus. RESULTS: This study included 266 HIV positive women, of which 67 (25.2%) were first diagnosed with HIV during pregnancy. Thirty percent (n=80) of the women had pregnancy complications after 24 weeks of gestation. Preterm delivery was noted in 72 (27%) patients. Other complications included preeclampsia (n=7; 2.6%) and gestational diabetes (n=7; 2.6%). Older maternal age was the only risk factor associated with adverse pregnancy outcomes (adjusted odds ratio: 1.06, 95% confidence interval 1.01-1.12, P=0.02). CONCLUSIONS: HIV positive women, especially with advanced maternal age, have high-risk pregnancies and should be monitored as in an interdisciplinary setting. The preponderance of initial HIV diagnosis during pregnancy confirms the importance of HIV screening in pregnant women.