• Maternal third trimester pharmacokinetic (PK) measures (AUC and Cmax) [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  
• Endometrial tenofovir levels [ Time Frame: At Hours 1, 2, 4, 6, 8, 12, and 24 after drug administration ] [ Designated as safety issue: No ]
  
• Placental transfer (cord blood tenofovir levels, placental tissue tenofovir levels, and amniotic fluid tenofovir levels) [ Time Frame: At Hours 1, 2, 4, 6, 8, 12, and 24 after drug administration ] [ Designated as safety issue: No ]
  

There is an urgent need for HIV prevention methods that women can initiate and control themselves. Topical microbicides represent one such method. Tenofovir 1% vaginal gel was chosen as a high priority microbicide candidate due to its activity in target cells for HIV infection of the vagina and cervix and the low frequency of local and systemic toxicity observed in a prior HIV Prevention Trials Network (HPTN) trial utilizing tenofovir 1% gel. The purpose of this study is to assess term pregnancy single-dose pharmacokinetics (PK) of tenofovir 1% gel in HIV uninfected pregnant women.

The expected duration of participation for individually enrolled participants will depend on how early they enroll prior to the date of cesarean section, but may range from approximately 3 to 6 weeks. An initial screening/enrollment visit will occur approximately 1 to 4 weeks prior to the participant's scheduled cesarean section, but no more than 4 weeks before the delivery date. A targeted physical exam, medical and medication history assessment, blood and urine collection, and a pelvic exam will occur at screening/enrollment. Tenofovir gel will be administered vaginally approximately 2 hours before the expected time of cesarean section. On the day of gel administration and cesarean delivery, a targeted physical exam, medical and medication history assessment, a pelvic exam, maternal blood tenofovir level measurement, and collection of placental and endometrial tissues, cord blood, and amniotic fluid will occur.

After gel administration, PK measures will be taken at Hours 1, 2, 4, 6, 8, and 12; maternal blood tenofovir level measurement and a review of adverse events will also occur at these times. A 24-hour evaluation will occur between Hours 22 and 26. At this evaluation, a targeted physical exam, a review of adverse events, and tenofovir level measurement will occur. Each participant will be contacted between Days 10 and 18 to collect data on any adverse events they experience. In addition, an unscheduled visit may be necessary if an unresolved adverse event occurs on or after the 24-hour evaluation. If an unscheduled visit is required, the participant will undergo a targeted physical exam, medical and medication history assessment, blood and urine collection, a pelvic exam, and tenofovir level measurement.