PURPOSE:Although first-trimester vaginal bleeding is an alarming symptom, few studies have investigated the prevalence and predictors of early bleeding. This study characterizes first trimester bleeding, setting aside bleeding that occurs at time of miscarriage. METHODS:Participants (n = 4539) were women ages 18 to 45 enrolled in Right From the Start, a community-based pregnancy study (2000-2008). Bleeding information included timing, heaviness, duration, color, and associated pain. Life table analyses were used to describe gestational timing of bleeding. Factors associated with bleeding were investigated by the use of multiple logistic regression with multiple imputation for missing data. RESULTS:Approximately one fourth of participants (n = 1207) reported bleeding (n = 1656 episodes), but only 8% of women with bleeding reported heavy bleeding. Of the spotting and light bleeding episodes (n = 1555), 28% were associated with pain. Among heavy episodes (n = 100), 54% were associated with pain. Most episodes lasted less than 3 days, and most occurred between gestational weeks 5 to 8. Twelve percent of women with bleeding and 13% of those without experienced miscarriage. Maternal characteristics associated with bleeding included fibroids and prior miscarriage. CONCLUSIONS:Consistent with the hypothesis that bleeding is a marker for placental dysfunction, bleeding is most likely to be observed around the time of the luteal-placental shift.