Association between first-trimester subchorionic hematoma and pregnancy loss before 20 weeks of gestation in singleton pregnancies

To evaluate the association between a first-trimester subchorionic hematoma (SCH) and pregnancy loss before 20 weeks of gestation in singleton pregnancies. We conducted a retrospective cohort study of singleton pregnancies from January to December 2021. All patients had routine first-trimester ultrasound scans and were followed up for pregnancy outcomes. We compared pregnancy loss rates before 20 weeks in women with and without SCH and analyzed risk factors using logistic regression. Out of 1,144 singleton pregnancies, 559 (48.9%) had SCH. Women with SCH had higher rates of vaginal bleeding (38.1 vs. 23.2%, P < 0.001). SCH was independently associated with miscarriage before 20 weeks (adjusted OR 1.94, 95% CI 1.19-3.15). Earlier SCH diagnosis increased miscarriage risk (adjusted OR 2.71 for diagnosis before 7 weeks, 95% CI 1.45-5.07). SCH size was not linked to pregnancy loss, but "large" SCH increased placental abruption risk (adjusted OR 5.03, 95% CI 1.20-21.11). Dydrogesterone use appeared protective against miscarriage (adjusted OR 0.28, 95% CI 0.15-0.52). First-trimester SCH is associated with an increased risk of miscarriage before 20 weeks. Large SCHs increase the risk of placental abruption, while dydrogesterone use may reduce miscarriage risk.