In high HIV prevalence regions, women are at high risk for HIV during pregnancy and breastfeeding. To protect women and reach elimination of mother-to-child HIV transmission, the World Health Organization recommends offering oral tenofovir (TFV)-based pre-exposure prophylaxis (PrEP) to HIV-negative pregnant and postpartum women in high-burden settings. Although most pregnant Kenyan women with HIV risk factors accept PrEP when offered, >50% discontinue PrEP within 30 days of initiation and sub-optimal adherence is common. To date, no intervention studies to improve PrEP adherence include pregnant or postpartum women. The investigators adapted an SMS communication platform (mWACh) to send PrEP-tailored, theory-based SMS to facilitate adherence among pregnant women who initiate PrEP. In a non-randomized pilot, the investigators found that mWACh-PrEP recipients were more likely to persist with PrEP use and to self-report high adherence. The investigators propose a randomized trial to determine the effect of the mWACh-PrEP tool on PrEP adherence during pregnancy through the postpartum period. The investigators will also gather data on cost and delivery using the Proctor Implementation Outcomes Framework to expedite translation into routine practice. The overarching hypothesis is that mWACh-PrEP will improve PrEP adherence among mothers at-risk for HIV, be acceptable to patients and providers, and be cost-effective. The study will be executed via the following aims:

Aim 1- To determine the effect of the mWACh-PrEP tool on PrEP adherence during pregnancy through the postpartum period among women who initiate PrEP within ANC-PrEP. We will conduct a 2-arm randomized trial comparing mWACh-PrEP vs standard of care (SOC, i.e. in-clinic adherence counseling) among HIV-uninfected pregnant women with high HIV acquisition risk (defined by validated risk score) who initiate PrEP. The primary outcome will be adherence at 6 months postpartum (TFV hair levels >0.038 ng/mg; consistent with 7 pills/ week). Secondary outcomes will include sexually transmitted infection (STI) incidence, adherence cofactors, and prevention-effective adherence (time-varying alignment of adherence with risk behaviors). Exploratory outcomes will include HIV incidence and perinatal outcomes by arm. Hypothesis: mWACh-PrEP will increase PrEP adherence compared to SOC.

Aim 2- Evaluate barriers and facilitators of mWACh-PrEP implementation within routine ANC. Using the Proctor framework, we assess acceptability and feasibility by conducting interviews and focus-groups with ANC-PrEP users, providers, and health planners. Hypothesis: Indications for readiness of mWACh-PrEP will be identified.

Aim 3- Estimate the cost-effectiveness of implementing mWACh-PrEP within ANC-PrEP, per HIV infection and disability-adjusted life-year (DALY) averted. We use data from Aims 1 and conduct micro-costing and time-and-motion studies to estimate the cost of mWACh-PrEP from a payer perspective. The incremental cost-effectiveness ratio (ICER) per HIV infection and DALY averted compared to SOC will be calculated. Hypothesis: Incorporating data on PrEP and ANC outcomes with improve ICERs for mWACh-PrEP.

Inclusion Criteria:

• Pregnant women presenting for routine antenatal care (ANC) who are:
• ≥18 years old
• 24-32 weeks gestation
• No documented tuberculosis infection
• HIV negative (based on ANC HIV testing)
• Plan to reside in area for at least one year postpartum
• Plan to receive antenatal, postnatal, and infant care at study facility
• Initiated PrEP during routine ANC
• Have an HIV risk score >6 (based on Pintye et al 2017).

Exclusion Criteria:

• Do not plan to remain in the study site catchment area for at least 1 year
• Do not have mobile phones.