ultrasound edd

my EDD from the first ultrasound po was OCT 8, tapos ng pa ultrasound ako ulit last july 11 for checkin of my cervix and ung film napansin lang ng asawa ko nkalagay is OCT 1 EDD na hehe so bakit po kaya ngbago, . thurs ko p mkausap ulit dra, hoping baka lang po meron may alam ng reaosn dto.. THANK YOU ???