Child death after born

There can be any number of reasons, but that number of deaths would likely result in either an inquest (if foul play was suspected) or an investigation into a hospital's practices.

A tip - if you are close to this woman, ask her. If she is someone you are considering marrying, maybe ask her to get genetics counseling with you. And keep in mind that, if having a child with her is not a good idea, there are other ways to become a parent. Don't use it as an excuse if you don't wish to marry - and don't call off a wedding because of such things.

If you're not that close to her, then you're just being nosy and should butt out.