When pregnant, without being on iron tablets is black poo normal?

No: Anytime you have black bowel movement you should have it tested to make sure there is no blood. It is an easy test at your doctor's office. Black tarry stool that tests positive for blood (heme) can mean bleeding from upper GI tract such as stomach and duodenum and requires further testing such as upper endoscopy.

Black Stools: If you are not taking supplements with iron, it may mean a possible bleed in your stomach . Observe what you ate a day or two before you had dark stools. Some foods may produce stools with that characteristic. If it is persistent, have it checked out. Make sure you are not taking meds like Aspirin or ibuprofen. It can also cause GI bleeding.