The effects of first-trimester subchorionic hematoma on pregnancy outcomes: a retrospective cohort study

Although first-trimester subchorionic hematoma (SCH) always concerns expectant parents, its clinical significance remains controversial. This study aimed to examine the relationship between SCH and its association with subsequent miscarriage and other perinatal outcomes in singleton pregnancies.

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 of SCH with maternal and neonatal outcomes.

A total of 815 (1.87%) SCH cases were detected in the first-trimester ultrasound examinations. The rate of miscarriage was statistically significantly higher in women with SCH than without [35.21% vs. 23.92%, 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 (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; P_trend < 0.01]. In addition, women with SCH volume ≥ 1 ml showed higher risk than did those with SCH volume < 1 ml [adjusted RR (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.

First-trimester SCH, particularly when characterized by early presence and large size, might significantly increase the risk of miscarriage. Data from this study suggest no associations between SCH and other maternal and neonatal outcomes.