What's an incompatent cervix and why do women have it?

Your OB: Should have explained that to you already or to your friend or daughter if that is their problem, iot is where the cx opens up too soon anytime after 15 weeks and u can lose the pregnancy, it can be caused by previous surgery or just weak tissue of the cervix, it is the standard of care at least where I do OB that all OB pts get the length of their cx. Measured in the 2nd tri to make sure not sho.