What could cause an unexplained termination of pregnancy?

Many causes can resu: Result in an unsuccessful preg , such as chromsome prob of the fetus, hormone problems , not attching properly to the endometrium, 1 spon ab is very common and usually does not require a workup but most obgyns would rec a workup if you have 3 in a row and many rec testing if u have 2 in a row but after one assuming u have no strange health problems your risk for another is not increased.