my wife is in 21 week and 2 days pregnancy, and yesterday we had an u/s, and doctor said she had placenta grade 1, anterior low lying 1.8cm from internal os, and she said maybe need to do through operation for the birth, and we scheduled in 12 more week to do another u/s. my question is: is it dangerous to have like my wife has right now? is it normal for 21 week pregnancy? and how many cm from internal os that women can give birth naturally? thx very much for your co-operation