dating a pregnancy

Posted By Tiffany on May 16, 1998 at 01:02:08:







I am currently pregnant with my third child.  My first was born right on the due date according to my last period.  (There was no ultrasound done)  My second was born twelve days late according to my last period but a week early by the ultrasound done around 22 weeks.  Now, with my third pregnancy, I once again have two different due dates--eleven days apart (the ultrasound done around 20 weeks being the later date).  How can there be such a discrepency when my periods have always been quite regualar?  My doctor is having a hard time dating my pregnancy because I never get very big  (My babies have been close to 8 pounds).  He says he wouldn't be surprised if I go over the latest due date even.  Could birth control pills taken the month before I became pregnant affect my cycle?