Associations between extreme temperature exposure and hypertensive disorders in pregnancy: a systematic review and meta-analysis

Background: Hypertensive disorders in pregnancy (HDP) are a major cause of maternal mortality and morbidity. Recent studies indicated that pregnant women are the most vulnerable populations to ambient temperature influences, but it affected HDP with inconsistent conclusions. Our objective is to systematically review whether extreme temperature exposure is associated with a changed risk for HDP. Method: We searched PubMed, EMBASE, Web of Science and Cochrane Library databases. We included cohort or case control studies examining the association between extreme temperature exposure before or during pregnancy and HDP. Heat sources such as saunas and hot baths were excluded. We pooled the odds ratio (OR) to assess the association between extreme temperature exposure and preeclampsia or eclampsia. Results: Fifteen studies involving 4,481,888 patients were included. Five studies were included in the meta-analysis. The overall result demonstrated that in the first half of pregnancy, heat exposure increases the risk of developing preeclampsia or eclampsia and gestational hypertension, and cold exposure decreases the risk. The meta-analysis revealed that during the first half of pregnancy, heat exposure increased the risk of preeclampsia or eclampsia (OR 1.54, 95% confidence interval (CI): 1.10, 2.15), whereas cold exposure decreased the risk (OR 0.90, 95% CI: 0.84, 0.97). Conclusion: The ambient temperature is an important determinant for the development of HDP, especially for preeclampsia or eclampsia. The effects of extreme temperatures may be bidirectional during the different trimesters of pregnancy, which should be evaluated by future studies. This review provided hints of temperature regulation in HDP administration.