Subchorionic hematomas are increased in early pregnancy in women taking low-dose aspirin.

Objective: To determine the frequency of subchorionic hematomas (SCH) in first-trimester ultrasound examinations of patients with infertility and recurrent pregnancy loss (RPL) and in patients from a general obstetric population. To determine if the method of assisted reproduction utilized or the use of anticoagulants, such as heparin and aspirin (ASA), influenced frequency of SCH.

Design: Prospective, cohort study.

Setting: Fertility clinic and general obstetrics clinic.

Patient(s): Five hundred and thirty-three women who were pregnant in the first-trimester.

Interventions: Not applicable.

Main Outcome Measure(s): Frequencies of subchorionic hematomas in women based on diagnosis, use of anticoagulants, and fertility treatment.

Result(s): SCH were identified in 129/321 (40.2%) in the study group compared to 23/212 (10.9%) in the control group. Fertility diagnosis and the use of heparin did not appear to affect the frequency of SCH in the first trimester; however, SCH occurred at an almost four-fold increase in patients taking ASA compared to those not taking ASA, regardless of fertility diagnosis or method of fertility treatment.

Conclusion(s): The use of ASA may be associated with an increased risk of developing a SCH during the first trimester. The increased frequencies of SCH in pregnancies of patients attending a fertility clinic compared to women from a general obstetrical practice was highly correlated with the use of ASA.