What is the normal cervical length at 12 weeks. mine was 3.1cm. is it normal? i had a previous loss at 20 weeks for no known reason.

20 week loss: The most important issue here is that your doctor make a judgment call regarding your last pregnancy in order to manage this one. Using the information they have they need to determine the most likely cause of the the 20 week loss. If it was preterm labor then 17 Hydroxy Progesterone injections should be used. If they feel cervical incompetence was likely then they should perform a cerclage.