The Effects of First-trimester Subchorionic Hematoma on Pregnancy Outcomes:A Retrospective Cohort Study

Background: Although first-trimester subchorionic hematoma (SCH) always concerns expectant parents, its clinical significance remains controversial. This study aimed to examine the relationship between first-trimester 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 first trimester and then were followed up for maternal and neonatal outcomes. SCH was detected in the first-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 first-trimester ultrasound examination. The rate of miscarriage was statistically significantly higher in women with SCH than in those without [35.2% vs. 23.9%, P<0.01; adjusted relative risk (RR):1.44, 95% confidence 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 significant difference in the rates of other pregnancy outcomes between women with and without SCH. Conclusions: : First-trimester SCH might significantly 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.