Background: Although rst-trimester subchorionic hematoma (SCH) always concerns expectant parents, its clinical signi cance remains controversial. This study aimed to examine the relationship between rsttrimester SCH and its association with subsequent miscarriage and other perinatal outcomes.Methods: We conducted a retrospective cohort study including 43,660 women who underwent routine prenatal care since the rst trimester and then were followed up for maternal and neonatal outcomes.SCH was detected in the rst-trimester ultrasound examinations. Robust Poisson regression was used to estimate adjusted risk associations between SCH maternal and neonatal outcomes.Results: A total of 815 (1.87%) SCH were detected in the rst-trimester ultrasound examination. The rate of miscarriage was statistically signi cantly higher in women with SCH than in those without [35.2% vs.23.9%, P<0.01; adjusted relative risk (RR):1.44, 95% con dence interval (CI): 1.31-1.58]. Subgroup analysis of women with SCH showed a clear trend that the earlier SCH occurred, the higher the risk of miscarriage was [adjusted RR and 95% CI for onset at the gestational weeks of 8-9, 6-7, and <6 vs. ≥10: 1.30 (0.69-2.46), 2.33 (1.28-4.23), and 4.18 (2.30-7.58), respectively; Ptrend<0.01]. In addition, women with SCH volume ≥1ml showed higher risk than those <1 ml [adjusted RR and 95% CI for 1-4.9 ml, and ≥5 ml vs. <1 ml: 1.36 (1.10-1.68) and 1.56 (1.18-2.07), respectively]. There was no statistically signi cant difference in the rates of other pregnancy outcomes between women with and without SCH.Conclusions: First-trimester SCH might signi cantly increase the risk of miscarriage, particularly the one that occurs early and the one with large size. Data from this study do not suggest adverse effects of SCH on other maternal and neonatal outcomes.