Association Between First-Trimester Subchorionic Hematomas and Pregnancy Loss in Singleton Pregnancies

OBJECTIVE: To assess the association of a first-trimester subchorionic hematoma with pregnancy loss in women with singleton pregnancies. METHODS: We conducted a retrospective cohort study of all women with singleton pregnancies presenting for prenatal care before 14 weeks of gestation over a 3-year period at a single obstetric practice. All patients had routine first-trimester ultrasound scans. We reviewed ultrasound data from the first ultrasound scan performed between 6 0/7 and 13 6/7 weeks of gestation and compared rates of pregnancy loss before 20 weeks in women with and without a subchorionic hematoma. Logistic regression analysis was used to control for potential confounding variables. RESULTS: From January 2015 to December 2017, a total of 2,446 women met inclusion criteria, 451 (18.4%) of whom had subchorionic hematomas. Women with subchorionic hematomas had their first ultrasound scans at an earlier gestational age (8 5/7 vs 9 6/7 weeks of gestation, P<.001) and were more likely to have vaginal bleeding (33.3% vs 8.1%, P<.001). Maternal age, race, use of in vitro fertilization, body mass index, prior number of losses, and medical comorbidities did not differ between the groups. On univariable analysis, subchorionic hematoma was associated with an increased risk of pregnancy loss before 20 weeks of gestation (7.5% vs 4.9%, P=.026); however, after adjusting for gestational age and vaginal bleeding, this association was no longer significant (adjusted odds ratio 1.13, 95% CI 0.74-1.74). In the 451 women with subchorionic hematomas, no characteristics of the subchorionic hematoma, including size by volume, largest diameter, presence of vaginal bleeding, and presence of an additional subchorionic hematoma, were associated with pregnancy loss. Post hoc power analysis showed we had 80% power to detect an increase in pregnancy loss before 20 weeks of gestation from 4.9% in women with no subchorionic hematoma to 8.3% in women with subchorionic hematoma. CONCLUSION: In this cohort of women with singleton pregnancies, subchorionic hematoma before 14 weeks of gestation was not independently associated with pregnancy loss before 20 weeks of gestation.