Objective: Our objective was to determine whether chronic exposure to ambient H2S due to sargassum strandings is associated to increased occurrence of preeclampsia in Martinique, a French Caribbean Island. Design: Observational case control study Settings and population: Data for this study derive from 25/01/2016 to 31/07/2020 births database of the University Hospital of Martinique. Methods: Women were considered exposed to H2S if living and/or working in cities along the Atlantic coast of Martinique known to be impacted by sargassum strandings. Main Outcome Measures: Primary endpoint was occurrence of preeclampsia as defined by the International Society for the Study of Hypertension in Pregnancy in 2018. Secondary endpoint was preeclampsia free survival time, which was defined by the number of months free of preeclampsia between the 20th and 37th week of amenorrhea. Results: In the exposed population, median H2S concentration, averaged across pregnancy length, was 300 ppb (IQR H-spread 197). There were no differences (p=0.20) in preeclampsia incidence rate between H2S exposed (n=623) and non-exposed (n=2367) pregnant women during the follow-up period (7.5% versus 6.1%, respectively). Time to preeclampsia between the 20th and 37th week of amenorrhea was shorter (p=0.02) in H2S exposed compared with non-exposed pregnant women (median=30.9 months - IQR 8.6 versus 32.9 months - IQR 6.0, respectively) Conclusions: We found that onset of preeclampsia was earlier in women living and/or working in areas impacted by sargassum seaweed strandings compared with non-exposed pregnant women. Funding: None