How many centimeters long should the cervix be before they can decide that effacement has begun?
your dilation and effacement are two different things. When your cervix is effaced that means it is thinned out and dilation is the opening. For example I am currently 1cm dilated and my cervix is 90% effaced. Your doc can tell how effaced you are at any point just by feeling your cervix. Next drs. appointment just ask him to check for you.