The probability of acquiring HIV-1 per condomless sex act increases through pregnancy and is highest during the postpartum period, according to data published in the Journal of Infectious Diseases.1

Investigators applied a log-log model and data from 2751 HIV-1 serodiscordant couples to assess the differential risk for HIV-1 infection across reproductive stages by calculating per-coital-act risk in each stage and comparing with nonpregnant times.

After adjusting for condom use, preexposure prophylactic use, and HIV-1 viral load, the per-act probability was higher in late pregnancy (adjusted relative risk, 2.82; P =.01) and postpartum (adjusted relative risk, 3.97; P =.01) compared with nonpregnant times. 

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Further, the acquisition probability per condomless act for women aged 25 years, not taking preexposure prophylactics, and whose partners’ viral load is 10,000 copies/mL was 0.0011 (95% CI, 0.005-0.0019), 0.0022 (95% CI, 0.0004-0.0093), 0.0030 (95% CI, 0.0007-0.0108), and 0.0042 (95% CI, 0.0007-0.0177) in nonpregnant, early, late pregnant, and postpartum periods, respectively.

The results demonstrate that HIV-1 acquisition risk increases 3-fold to 4-fold in late pregnancy and postpartum periods, even after adjustments for factors known to affect acquisition. According to an independent editorial2 published about this work, “because the study was able to control for major behavioral, demographic and clinical confounders, these data strongly point toward a biologic association of pregnancy with HIV-acquisition risk.” This has important implications for efforts toward elimination of mother-to-child transmission, as well. The editorial concluded: “Elimination of [mother-to-child transmission] will not occur without elimination of new infections among women.”

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Although further research is required to understand the biological basis of susceptibility during these periods, authors of both articles recommend treating HIV-seronegative pregnant and postpartum women in endemic areas as an at-risk population and increasing prevention, counseling, and testing.


  1. Thomson KA, Hughes J, Baeten J, et al. Increased risk of female HIV-1 acquisition throughout pregnancy and postpartum: a prospective per-coital act analysis among women with HIV-1 infected partners. [published online March 5, 2018]. J Infect Dis. doi: 10.1093/infdis/jiy113
  2. Mofenson LM. Risk of HIV acquisition during pregnancy and postpartum: a call for action [published online March 5, 2018]. J Infect Dis. doi: 10.1093/infdis/jiy118