Friend started dilating at 21 weeks, was forced to deliver, baby died. doc diagnosed her w/'weak cervix?' why did it happen? can i avoid it myself?

Early cervix opening: Early cervical dilation is not as uncommon as one might think. However, there are very good ways to check for this now and follow women who have a history of early dilation. Ultrasound can detect cervical shortening, and if this is noted, a cerclage can be placed to try and prevent early cervical dilation. It's not really known why this happens, but can be detected and treated before a dead baby.