I have an 20 month old daughter born via cesarean at 35 weeks due to abruption. 

My doctor is now telling me, even though he agreed to a vbac, that my son's head circumference is 36cm at 39 weeks and that I am showing no signs of going into labour.  He is worried that after 40 weeks the head will lose some of its ability to mold and fit through the birth canal.  Is there any research to support the calcification of the bones after 40 weeks and that baby's head, past 40 weeks, do not mold as much?

Di