The relationship between first-trimester subchorionic hematoma, cervical length, and preterm birth.

OBJECTIVE: The objective of the study was to evaluate the association between a sonographically diagnosed subchorionic hematoma (SCH) in the first trimester and subsequent midtrimester cervical length and preterm birth.

STUDY DESIGN: In this cohort study, 512 women with an SCH on their first-trimester ultrasound were compared with 1024 women without a first-trimester SCH. All women underwent routine transvaginal cervical length measurement between 18 and 22 weeks. Women with multifetal gestation, cerclage, or a uterine anomaly were excluded. A multivariable linear regression was performed to assess the independent association of SCH with cervical length, and a logistic regression was done to determine whether the presence of SCH was associated with preterm birth independent of the cervical length.

RESULTS: In a univariable analysis, the presence of a SCH was significantly associated with a shorter mean cervical length as well as a cervical length less than the 10th percentile (4.27 cm vs 4.36 cm, P = .038; 1.9% vs 0.5%, P = .006, respectively). Preterm birth also was more common in women with an SCH (12.5% vs 7.3%, P = .001). Even after adjusting for potentially confounding factors, a significant negative association existed between the presence of an SCH and cervical length (centimeters) (linear regression coefficient, -0.08; 95% confidence interval, -0.17 to -0.005). In a multivariable regression, SCH remained associated with preterm birth, even with cervical length entered into the equation as a covariate (adjusted odds ratio, 1.58; 95% confidence interval, 1.09-2.32).

CONCLUSION: First-trimester SCH is associated with both a shorter cervical length and preterm birth. Our data suggest, however, that mechanisms other than cervical shortening may be involved in preterm birth among women with SCH.