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Extent of in-utero transfer of tenofovir from mother to fetus: a paired analysis of hair specimens collected at birth from a cohort in the United States.

Understanding in-utero transfer of antiretrovirals is critical for interpreting safety. Hair levels measure cumulative exposure. We measured tenofovir concentrations in hair at delivery among women living with HIV receiving tenofovir-disoproxil-fumarate-based treatment and their infants using liquid chromatography/tandem mass-spectrometry. Among 103 mother-infant pairs, the mean log10-ratio of infant-to-maternal tenofovir levels was 1.08 (95% CI 0.97-1.20). TFV transfer was 60% lower from mothers who had preterm deliveries compared to term and 42% lower from mothers who had C-section deliveries compared to vaginal. Like prior studies assessing transfer via short-term measures (plasma, cord blood, amniotic fluid), we found high cumulative transfer using hair.