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.