Uterus didelphys is a condition you're born with where you have two banana-shaped uteruses which are separate from each other. Sometimes there will be two cervixes, and sometimes even a double vagina.

Illustration courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 11115

It's estimated that around 1 in 3000 have two uteruses, but it could be as many as 1 in 1000 or as few as 1 in 10000 - since the condition doesn't always have symptoms and we don't routinely count how many internal organs everyone has, it's hard to say for sure. Uterus didelphys is usually noticed in those who have some symptoms, or coincidentally during pelvic imaging or surgery.

Symptoms of uterus didelphys if they're present include heavy or painful periods (because you're having two periods at once), bleeding that isn't stopped by a tampon (because it's only absorbing blood from one vagina and uterus), and pain during sex. In terms of pregnancy, recurrent miscarriages, pre-term birth and the baby being in the breech position are more likely.

Having two uteruses also comes with an increased chance of only having one kidney, or having endometriosis. There's also a risk of dangerous build-up of menstrual blood if one uterus doesn't have access to a cervix.

However, lots of people don't have any symptoms at all, and might be surprised to learn during a routine pregnancy scan or other medical test that there's two wombs knocking about in there.