The plural of uterus is uteri or uteruses.
The muscular organ in female mammals used to house a fetus. Also known as a womb.
The word uterus dates back to the 14th Century and is derived from Latin. As such the plural of uterus according to Latin rules is uteri.
However its plural form according to English rules is uteruses.
Both forms of the word are acceptable although uteri is more common than uteruses, especially in academic writing.
The graph below shows the appearances of both plural forms of uterus in written English language since 1900. As you can see the word uteri was historically much more common in usage, although the difference is smaller these days.
Singular Example: A woman's uterus is incredibly flexible. Starting from only around 2.5 inches before pregancy to the size of a watermelon towards the end of the pregnancy.
Plural Example: Although it is very rare, some women have two uteruses. According to research this condition can occur when two tubes fail to morph together as they would usually.
The graph shows the occurances of the plural of uterus in written English since 1800 using Google's Ngram Viewer.