Rectal bleeding during pregnancy: causes

By trimester

Weeks 1–13

1st trimester

Hemorrhoids and fissures are less common this early, but the constipation that drives both often begins now as progesterone rises and prenatal iron firms up stool. Building fiber and fluid habits early can head off bleeding before it starts.

Weeks 14–27

2nd trimester

Growing uterine pressure adds to constipation as a trigger around this stage, so hemorrhoids and the bleeding that comes with them often show up or worsen now. New bleeding is still worth mentioning at a visit rather than assuming it is routine.

Weeks 28–birth

3rd trimester

Hemorrhoids and fissures peak in the third trimester from maximum uterine pressure and the pushing of labor itself. It can be tempting to assume all late-pregnancy bleeding is routine, but bleeding that is heavy, mixed through the stool, or paired with pain, fever, or dizziness still needs the same same-day evaluation regardless of trimester.

What does the evidence show for blood in stool?

• Hemorrhoids are extremely common in pregnancy, with some series reporting rates as high as 75 to 85 percent, and along with anal fissures, which affect roughly 3 percent of pregnancies, they account for the large majority of rectal bleeding in pregnancy. Inflammatory bowel disease and colorectal cancer are far less common but real causes to rule out. 1
• Bright red blood on the stool, on toilet paper, or in the toilet bowl is the typical hemorrhoid bleeding pattern, but not every anal symptom is caused by a hemorrhoid, since rectal bleeding can also come from conditions like Crohn's disease, ulcerative colitis, or colorectal cancer. 2
• Anal fissures typically cause bright red bleeding that appears as streaks rather than heavy bleeding, along with severe pain during a bowel movement that can persist for hours afterward, a different pain pattern than hemorrhoids usually cause. 3
• Black or tarry stool, dizziness, fainting, or fatigue can signal more significant gastrointestinal bleeding, and symptoms of shock, including a rapid heart rate, pale or cold skin, confusion, or fainting, need immediate medical attention. 4
• Reviewers emphasize that pregnancy should not delay a needed evaluation for rectal bleeding: standard investigations like endoscopy and imaging are considered safe when clinically indicated, and inflammatory bowel disease left unmanaged in pregnancy carries real risks, including higher rates of miscarriage, fetal growth restriction, and preterm delivery. 1

When should I call my provider about blood in stool?

Black or tarry stool, dizziness, fainting, a racing heartbeat, or pale, cold, clammy skin are signs of more significant blood loss and need immediate medical attention rather than a wait-and-see approach. Heavy bleeding, bleeding mixed throughout the stool rather than just on its surface, or bleeding alongside abdominal pain, fever, or diarrhea also deserve a same-day call, since these point away from ordinary hemorrhoids or a fissure. Pregnancy is not a reason to delay an evaluation: reviewers note that standard tests like endoscopy are considered safe in pregnancy when there is a real reason to look further. When in doubt, call your obstetric team the same day. Early input almost always beats waiting, and the on-call line exists exactly for this.