Cervical lengths!

Hey all just asking if when you are pregnant if cervical lengths are measured at 16 weeks. I recently had two miscarriages and asked about what if I needed a cerclage and my doctor said it is usually measured at 16 weeks but I’m hoping I make it to 16 weeks next time. Please advise if it is usually not done before 16 week and if it is done before 16 weeks what test did u have done or what made tour doctor know to do it earlier in pregnancy? Thanks in advance!

-Annamaria