I have a history of having small sized babies. Today my obgyn's nurse called me with my estimated due date. Which is 16 off of the due date I have calculated. Could my history of small children be a factor as to why my due date is so far off? LMP was February 18th nurse states with the due date they came up with my LMP was March 4th. However I know I did not have a MP in the month of March.