Background:  The study objective was to maximize the number of HIV⁺ women who received ARV prophylaxis for prevention of mother-to-child transmission (PMTCT) at delivery in public facilities in Swaziland. HIV prevalence among pregnant women is 42% and uptake of PMTCT is high. PMTCT guidelines stipulate that women who tested HIV^– >3 months prior to delivery should be retested. Women who seroconvert during pregnancy often miss the opportunity for antiretroviral (ARV) prophylaxis.

Methods:  With a quasi-experimental design, the study added retesting of eligible HIV^– women as a standard of care to existing PMTCT services in 3 of 6 maternity units in Swaziland. HIV status on arrival in maternity was recorded. Women who retested HIV⁺ were provided prophylaxis as per national guidelines. Cord blood was tested for HIV and ARV presence as a measure of completion of the PMTCT cascade from HIV testing to ingestion of prophylaxis before delivery. Contingency tables and c² tests were used to summarize data and test for associations between frequencies of events.

Results:  Of 2444 women enrolled, 1398 (62.3%) had tested HIV^– in ANC, representing 388 person-years of observation. By delivery, 58 women seroconverted. Cumulative incidence was 4.4% (average time of exposure, 3 months). HIV incidence rate was 16.75 new infections per 100 person-years. A greater proportion of women were eligible for retesting in the control sites (386 or 55%) as compared to (263 or 38%) in intervention sites. In comparing the proportion of seroconvertors receiving ARV prophylaxis before delivery, a significant difference was found between the intervention and control sites:  54.2% (13 of 24) women who seroconverted in the intervention group received ARV prophylaxis, compared to only 26.5% (9/34) of those in the control group (χ² = 4.58, P = 0.03). Using Ministry of Health program data, we found that control sites had retested only 14% (135 of 959) HIV^– women, as compared to 45% (528 of 1185) women at intervention sites (χ² = 230.52, P <0.0001; relative risk 3.17 (95%CI 2.67 to 3.74).

Conclusions:  In high-prevalence settings, the incidence of HIV during pregnancy is also high. Reaching women who seroconvert late in pregnancy cannot be an afterthought for PMTCT programs. These women often have acute infection with assumed higher viral loads and greater risk of transmitting infection to their infants. Routine offer of retesting for all HIV^– women is critical to reduce infection rates of infants in high-prevalence countries.