BACKGROUND: Pregnancy may increase a woman's susceptibility to HIV. Maternal HIV acquisition during pregnancy and lactation is associated with increased perinatal and lactational HIV transmission. There are no published reports of preexposure prophylaxis use after the first trimester of pregnancy or during lactation. OBJECTIVE: The purpose of this study was to report the use of preexposure prophylaxis and to identify gaps in HIV prevention services for women who were at substantial risk of HIV preconception and during pregnancy and lactation at 2 United States medical centers. STUDY DESIGN: Chart review was performed on women who were identified as "at significant risk" for HIV acquisition preconception (women desiring pregnancy) and during pregnancy and lactation at 2 medical centers in San Francisco and New York from 2010-2015. Women were referred to specialty clinics for women who were living with or were at substantial risk of HIV. RESULTS: Twenty-seven women who were identified had a median age of 27 years. One-half of the women had unstable housing, 22% of the women had ongoing intimate partner violence, and 22% of the women had active substance use. Twenty-six women had a male partner living with HIV, and 1 woman had a male partner who had sex with men. Of the partners who were living with HIV, 73% (19/26) were receiving antiretroviral therapy, and 42% (11/26) had documented viral suppression. Thirty-nine percent (10/26) of partners had known detectable virus, and 19% (5/26) had unknown viral loads. Women were identified by clinicians, health educators, and health departments. Approximately one-third of the women were identified preconception (8/27); the majority of the women were identified during pregnancy (18/27) with a median gestational age of 20 weeks (interquartile range, 11-23), and 1 woman was identified in the postpartum period. None of the pregnant referrals had received safer conception counseling to reduce HIV transmission. Twenty-six percent of all women (7/27) were eligible for postexposure prophylaxis at referral, of whom 57% (4/7) were offered postexposure prophylaxis. In 30% (8/27), the last HIV exposure was not assessed and postexposure prophylaxis was not offered. The median time from identification as "at substantial risk" to consultation was 30 days (interquartile range, 2-62). Two women were lost to follow up before consultation. One woman who was identified as "at significant risk" was not referred because of multiple pregnancy complications. She remained in obstetrics care and was HIV-negative at delivery but was lost to follow up until 10 months after delivery when she was diagnosed with HIV. No other seroconversions were identified. Of referrals who presented and were offered preexposure prophylaxis, 67% women (16/24) chose to take it, which was relatively consistent whether the women were preconception (5/8), pregnant (10/15), or after delivery (1/1). Median length of time on preexposure prophylaxis was 30 weeks (interquartile range, 20-53). One-half of women (10/20) who were in care at delivery did not attend a postpartum visit. CONCLUSION: Women at 2 United States centers frequently chose to use preexposure prophylaxis for HIV prevention when it was offered preconception and during pregnancy and lactation. Further research and education are needed to close critical gaps in screening for women who are at risk of HIV for pre- and postexposure prophylaxis eligibility and gaps in care linkage before and during pregnancy and lactation. Postpartum women are particularly vulnerable to loss-to-follow-up and miss opportunities for safe and effective HIV prevention.