Background: HIV infection and its management during pregnancy to reduce perinatal transmission has been associated with preterm birth (PTB). This management has drastically changed. We aimed to evaluate changes in rates of PTB over 34 years in women living with HIV (WLWH) in Switzerland, and to identify factors and interventions associated with these changes.

Methods: We analysed data from 1238 singleton pregnancies, prospectively collected by the Swiss Mother and Child HIV Cohort Study (MoCHiV) and the Swiss HIV Cohort Study (SHCS) between 1986 and 2020. Rates of PTB in this cohort were compared with that of the general Swiss population for three time periods according to changing treatment strategies recommended at the time. We evaluated the association of PTB with sociodemographic, HIV infection and obstetric variables in uni- and multivariate logistic regression.

Results: Rate of PTB in WLWH was highest prior to 2010 (mean 20.4%), and progressively decreased since then (mean 11.3%), but always remained higher than in the general population (5%). Older maternal age, lower CD4 count and detectable viraemia at third trimester (T3), drug consumption and mode of delivery were all significantly associated with both PTB and period of study in univariate analysis. There was no association between PTB and type of antiretroviral regimen. No difference was found in the rate of spontaneous labor between PTB and term delivery groups. Only higher CD4 count at T3 and vaginal delivery were significantly associated with a decrease in PTB over time in multivariate analysis.

Conclusions: Preterm birth in WLWH in Switzerland has drastically decreased over the last three decades, but remains twice the rate of that in the general population. Improved viral control and changes in mode of delivery (vaginal birth recommended if viral loads are low near birth) have led to this progress.