Knowing When It Matters: Gestational Age at First-Trimester Bleeding Episode and Features on Standardized Ultrasound Associate With Miscarriage Risk in a Prospective Pregnancy Cohort [ID 979]

INTRODUCTION: Bleeding is a common and distressing symptom in early pregnancy. Although most pregnancies with first-trimester bleeding result in live birth, the association between symptom timing and miscarriage risk is unknown. METHODS: Participants in a community-based prospective pregnancy cohort were recruited prior to conception or in early pregnancy. Participants provided information on timing, duration, and frequency of bleeding episodes in early pregnancy. Bleeding episodes that ended less than 4 days before a miscarriage were excluded from the analysis. Participants underwent a study ultrasound targeted for 6 weeks of gestation. We used Cox proportional hazards models to quantify the association between first-trimester bleeding and miscarriage risk and to assess whether risk was modified by gestational age at bleeding episode or features observed on standardized study ultrasound. RESULTS: Among 5,425 participants, 25.0% reported at least one episode of first-trimester bleeding and 12.0% of pregnancies ended in miscarriage. Bleeding was not associated with an overall risk of miscarriage (hazard ratio [HR] 0.93; 95% CI, 0.77–1.11). Only bleeding in week 9 of pregnancy was associated with an independent increase in miscarriage risk (HR 1.72; 95% CI, 1.14–2.60). First-trimester bleeding coupled with a greater than 4-day difference in observed versus expected features on ultrasound was associated with a fourfold increased risk of miscarriage (HR 4.21; 95% CI, 3.11–5.70). CONCLUSIONS/IMPLICATIONS: Implications of first-trimester bleeding for miscarriage risk are tied to gestational age at bleeding episode and features observed on ultrasound. This information can guide more specific patient counseling concerning risk.