Is a congenital anomaly in the cervix is dangerous?

It depends: Your question is not very precise. I would answer that if your congenital anomaly is about structure only and does not pose increase risk for bleeding or is not an obstruction probably not. However may pose risk for getting pregnant or maintaining pregnancy. If by congenital anomaly you mean some kind of dysplasia it may be dangerous. You really have to ask your doctor who knows more about you.