Causes of Dark Stool During Pregnancy

Pregnancy introduces many changes to nearly every system in the female body, including the digestive system. Dark stools can occur during pregnancy and may be accompanied by constipation depending on the cause of the dark stools. Discuss symptoms with a doctor to determine the cause, in case additional testing is required.


Anemia, or low red blood cell count, is a condition which frequently occurs during pregnancy. Iron supplements are often prescribed to help correct anemia. Some types of iron aren’t easily absorbed by the body. Dr. Marilyn Glenville explains that supplements ferrous sulfate and ferrous gluconate can cause black stools and constipation because the body can’t absorb and use the iron. To avoid dark stools associated with iron supplements, pregnant women can increase iron intake in their diet by eating iron rich foods including liver, red meat and green leafy vegetables.


Certain medications can cause stools to take on a very dark color. Pepto-Bismol, a popular over-the-counter medication used to treat upset stomachs, can cause dark stools. Patients should discuss the onset of black stools after beginning a new medication with a doctor to determine if the medication is to blame. Over-the-counter medication especially should be discussed with a doctor during pregnancy to ensure safety to the baby.


Dark stools can result from eating certain foods during pregnancy. Blueberries and licorice in particular are known to turn stools a dark color. Food colorings can also affect the stool color. Pregnant women can help identify the cause of their darkened stools by keeping a food journal each time darkened stools appear.


Bleeding that occurs within the digestive system will cause a color change in the stool. If the bleeding occurs in the stomach, the stool will appear very dark instead of bloody by the time it is passed, explains MedlinePlus. While it is far more common for iron supplements or foods to cause a change in stool color, a doctor may prescribe a special test to check for the presence of blood in a stool sample during pregnancy. The test is very non-invasive and patients are able to collect a stool sample from home and bring it into the doctor’s office for testing. The stool sample is applied to a small card and a chemical solution is applied which detects the presence of blood.

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