Participants in this unblinded study will be randomly assigned to one of three groups: standard individual prenatal care; standard CenteringPregnancy group prenatal care; or CenteringPregnancy Plus (CP+) group prenatal care. All participants assigned to either CenteringPregnancy or CP+ will have an initial individual medical exam. Groups will be formed based on participants' estimated delivery months, and will be led by a trained independent practitioner. There will be ten 2-hour group sessions between Weeks 16 and 40 of pregnancy. At each session, participants will first weigh themselves and take their blood pressure to chart their own progress. Individual prenatal assessments lasting approximately 30 minutes will be conducted by the practitioner. Participants will then have time to fill out handouts and self-assessments and engage in discussion with other group members. Discussions will focus on education and building prenatal, childbirth, and parenting skills. The CP+ sessions will include an HIV/STD risk reduction component in addition to all the elements of the standard CenteringPregnancy program. This additional feature will consist of interactive discussion, exercises, and skill-building activities targeted towards reducing HIV/STD risk behaviors. Participants assigned to receive standard individual prenatal care will not participate in group sessions, but will receive standard prenatal care. Outcome measures will include incidence of STD infection, rapid repeat pregnancy, degree of sexual risk behavior, perinatal and psychosocial factors.