- Nucleoside reverse transcriptase inhibitor (NRTI) backbones are not associated with the risk of preterm delivery (PTD).
- Risk of small-for-gestational-age (SGA) is less with TDF-XTC or ABC-3TC than with ZDV-3TC.
- Results support the safety of TDF-XTC backbones initiated in pregnancy with respect to gestation length and birth weight.
In this study, the authors focused on women starting ART (three/four drugs including at least two NRTIs) during pregnancy, a therapy preventing mother-to-child transmission of HIV. The results of previous studies, conducted in different populations, on the association of ART regimen with the risk of adverse pregnancy outcomes in pregnancy were inconsistent.
The study included HIV-positive women from resource-rich and middle-income settings in Western and Eastern Europe with a singleton pregnancy ending in a live birth in 2008-2014, conceived off treatment, and in which a single combination ART regimen started at least 2 weeks before delivery.
Of 7193 pregnancies enrolled, 45% (3207) were in the UK and Ireland, 44% (3134) in Ukraine and 7% (469) in Russia, with a smaller number in Belgium, Romania, Spain and Switzerland. The ART regimen included ZDV (zidovudine)–3TC (lamivudine) in 71% (n= 5122) of pregnancies, TDF-XTC (tenofovir) in 16% (n= 1122) and ABC (abacavir)–3TC in 10% (n= 711). Use of ZDV-3TC declined over time, with increasing usage of TDF-containing backbones. In 77% (n= 5558) the third agent was LPV/r (ritonavir-boosted lopinavir). Overall, 10% (722/7193) of deliveries were preterm and 11.1% (785/7089) of newborns were SGA.
Prevalence ratios were adjusted a priori for potential confounders. Specifically, for PTD model: calendar year and country of delivery, parity, maternal injection drug use (IDU) history, CD4+ cell count, maternal age, third agent in ART regimen. For the SGA model, all variables in the PTD model were included and additionally infant sex and ART duration.
In the main adjusted model (N=6123), there was no association between NRTI backbone and pre-term delivery for ABC-3TC.
In a different adjusted analysis (N=5780) infants exposed in utero to ABC-3TC or TDF-XTC were less likely to be born SGA than those exposed to ZDV-3TC.
This study carries limitations: patients at risk of pre-term delivery have by definition less opportunity to start ART in the later weeks, therefore ART duration in PTD analysis was not explored. Authors did not have available information on important confounders such as smoking, history of adverse pregnancy outcomes, infection. ART guidelines may be different from country to country.