Introduction: Sub-Saharan Africa has the largest number of people with HIV, one of the most severe burdens of adverse birth outcomes globally and particular vulnerability to climate change. We examined associations between seasonality and adverse birth outcomes among women with and without HIV in a large geographically representative birth outcomes surveillance study in Botswana from 2015 to 2018.

Methods: We evaluated stillbirth, preterm delivery, very preterm delivery, small for gestational age (SGA), very SGA, and combined endpoints of any adverse or severe birth outcome. We estimated the risk of each outcome by month and year of delivery, and adjusted risks ratios (ARRs) of outcomes during the early wet (1 November-15 January), late wet (16 January-31 March) and early dry (1 April-15 July) seasons, compared with the late dry (16 July-31 October) season. Analyses were conducted overall and separately by HIV status.

Results: Among 73 178 women (24% with HIV), the risk of all adverse birth outcomes peaked in November-January and reached low points in September. Compared with the late dry season, the ARRs for any adverse birth outcome were 1.03 (95% CI 1.00 to 1.06) for the early dry season, 1.08 (95% CI 1.04 to 1.11) for the early wet season and 1.07 (95% CI 1.03 to 1.10) for the late wet season. Comparing the early wet season to the late dry season, we found that ARRs for stillbirth and very preterm delivery were higher in women with HIV (1.23, 95% CI 0.96 to 1.59, and 1.33, 95% CI 1.10 to 1.62, respectively) than in women without HIV (1.07, 95% CI 0.91 to 1.26, and 1.19, 95% CI 1.04 to 1.36, respectively).

Conclusions: We identified a modest association between seasonality and adverse birth outcomes in Botswana, which was greatest among women with HIV. Understanding seasonal patterns of adverse birth outcomes and the role of HIV status may allow for mitigation of their impact in the face of seasonal extremes related to climate change.