Effects of heat exposure on self-reported heat strain symptoms among pregnant and postpartum women in South Africa.

Heat exposure can harm pregnant and postpartum women, yet heat strain symptoms in this population remain underexplored. This study implemented a novel mobile application and assessed the environmental context of five self-reported heat strain symptoms: skin rashes, sleep disturbances, dizziness, thirst, and exhaustion among pregnant and postpartum women in Tshwane, South Africa. Symptoms were assessed through interviewer-administered questionnaires at three time points over six months (N = 201). Self-reported heat strain was analysed against maximum Wet Bulb Globe Temperature (WBGTmax) and air temperature (Tmax). An additional symptom, wetness sensation, was collected continuously via self-reporting using the application and related to the Universal Thermal Climate Index (UTCI). Generalised Estimating Equation models and General Linear Mixed Models accounted for repeated measures. Four of five symptoms showed significant associations with both WBGTmax and Tmax. Wetness sensation was significantly correlated with UTCI. Thresholds for heat strain symptoms identified through Receiver Operating Characteristic curves ranged between 18.53 °C and 26.16 °C WBGTmax, reflecting differences in perceived severity. Urine specific gravity showed inconsistent association with heat, likely due to measurement timing limitations. Although risk varied across symptoms and threshold modelling was exploratory, this study highlights the adverse health consequences of heat exposure for pregnant and postpartum women, which may inform future interventions.