To analyze the related factors and pregnancy outcomes of patients with subchorionic hematoma (SCH) who experienced spontaneous abortion.

(1) A retrospective analysis was conducted on the clinical data of 491 patients with SCH who attended Dongguan Maternal and Child Health Hospital from February 2022 to August 2022. Pregnancy outcomes were followed up and relevant data were collected. (2) Based on the ratio of SCH volume to gestational sac volume, the 491 patients were divided into three groups: Group A (<20%, n=203), Group B (20%~50%, n=158), and Group C (>50%, n=130). (3) The gestational age at SCH onset, duration of SCH, pregnancy outcomes, and pregnancy complications were analyzed among the three groups.

The gestational age at SCH onset in the three groups was (8.51±1.71) weeks, (7.11±1.30) weeks, and (6.12±1.08) weeks, respectively (P<0.001). The duration of SCH was (3.06±1.98) weeks, (3.64±2.14) weeks, and (4.29±2.79) weeks, respectively (P<0.001), with statistically significant differences. The risk of spontaneous abortion in group B was 2.99 times that in group A (95%CI: 1.19~7.51, P=0.002), and the risk in group C was 7.51 times that in group A (95%CI: 3.18~17.70, P<0.001); The spontaneous abortion rate increased significantly with the increased in the ratio of SCH volume to gestational sac volume (3.9% vs. 9.5% vs. 22.35, P<0.001). There was no statistically significant difference in the incidence of pregnancy and childbirth complications (including preeclampsia, premature rupture of membranes, placental adhesion, and postpartum hemorrhage) among the three groups (P>0.05). The risk of spontaneous abortion in SCH patients with intrauterine lesions (including endometrial polyps, submucosal fibroids and intrauterine adhesions) was 3.46 times higher than that without such intrauterine lesions (95%CI: 1.54~7.78, P=0.003). The risk of spontaneous abortion decreased by 0.43 times for each additional term delivery (95%CI: 0.24~0.77; P=0.004). Among the 491 SCH patients, 52 (10.59%) experienced spontaneous abortion, of whom 25 underwent multiplex ligation-dependent probe amplification testing of chorionic villus. The tests revealed abnormal results in 17 patients.

In conclusion, larger SCHs appears at an earlier gestation age and persists longer. As the ratio of SCH to gestational sac volume increases, the spontaneous abortion rate increases significantly. Patients with SCH and intrauterine lesions have a significantly increased risk of spontaneous abortion, while patients with SCH who have previously delivered at term have a significantly reduced risk.