Seasonal ambient temperature and particulate matter as discriminators of hyperemesis gravidarum severity: a retrospective comparative observational study.

Introduction: Ambient air pollutants and temperature may influence the clinical severity of hyperemesis gravidarum (HG), but their relative contributions remain unclear. This study aimed to determine whether particulate matter (PM₁₀), sulfur dioxide (SO₂), and ambient temperature were independently associated with severe ketonuria in pregnant women with HG. Methods: This retrospective observational study included 211 pregnant women diagnosed with HG. Clinical severity was defined by ketonuria category (severe ≥2 + vs. non-severe <2+). Covariates (maternal age, gestational week, BMI, Healthy Eating Index [HEI], gravida, PM₁₀, SO₂, and ambient temperature) were selected Results: The autumn/winter group showed significantly higher maternal age, gravida, and PM₁₀ exposure, and lower ambient temperature than the spring/summer group (all Conclusion: Ambient temperature showed the strongest discriminative performance for HG severity among the environmental parameters examined, while the association of PM₁₀ was attenuated after adjustment for temperature. Maternal age was also independently associated with HG severity. These findings should be interpreted as associations rather than causal effects. Further prospective, multi-site studies incorporating individual-level exposure assessments are warranted to confirm these associations and elucidate the underlying mechanisms.