Vaginal Bleeding During Early Pregnancy By Emily E Bunce, MD, Wake Forest School of Medicine; Robert P Heine, MD, Wake Forest School of Medicine Reviewed / Revised Dec 2020 | Modified Sep 2022 View Patient Education Etiology Evaluation Treatment Key Points Topic Resources Some Causes of Vaginal Bleeding... Vaginal bleeding occurs in 20 to 30% of confirmed pregnancies during the first 20 weeks of gestation; about half of these cases end in spontaneous abortion.