How did you or your doctor determine your due date?

I read on this site that doctors determine your due date by your first day of your last period.  They then add 40 weeks to determine your due date. 

How did you (or your doctor) determine your due date?

The most accurate way of determining due date is through a sonogram. So you might just have to wait a little while. As for dating the pregnancy, I think 3 weeks is right but you are in your 4th or 5th week so they say 4 or 5 weeks. It is confusing.

I found a link for you, it lets you enter date of conception.

http://baby2see.com/duedate.html

I hope it helps.

I think you're actually 5 weeks.  You count from the first day of your last period, so although you conceived 3 weeks ago, you probably had your period 2 weeks before that-thus 5 weeks.  Then once you have your first ultrasound, you doctor will be able to give you a more accurate due date based on the size of the fetus.  Mine left my due date as is after the first ultrasound.   

Technically you would be 5 weeks.  It starts at the date of your last period.  When I was pregnant, my doctor did  a guestimate due date at first.  You go back three months and then add seven days.  For example if I was pregnant and my last period was april 1st, my due date would be around january 8th, 2009. 

Thanks guys! 

It is also important that your doc knows your period schedule.

I was a 35 day cycle so so docs were confused at first b/c the ultrasound was dating a week later.  That was until I explained again my cycle history.  The docs usually go by first day of last cycle as exact date of conception can be tricky.

For both my boys, my doctor went by the calculations provided by the sonogram (measurements of head and limbs combined with my estimate of last menstrual cycle).  The first one was accurate within 1 day, the second one was accurate within 12 hours.  I don't know if this is typical, but I was pretty impressed with the accuracy.

Yes, the doctors go by first day of your last period.  My problem was, I only had a vague idea of when that was.  I know it was like around December 15 somewhere, but I couldn't remember exactly when.  But I knew EXACTLY when baby was concieved because I had had only one accident.  So as you may guess, the date that the ultra sound gave as my due date, and the date that the pregnancy calculators you find online that can calculate from your date of conception where exactly the same.  September 23.

Original Post by santonacci:

For both my boys, my doctor went by the calculations provided by the sonogram (measurements of head and limbs combined with my estimate of last menstrual cycle).  The first one was accurate within 1 day, the second one was accurate within 12 hours.  I don't know if this is typical, but I was pretty impressed with the accuracy.

Wow!  That's amazing how accurate the due dates were. 

I was charting, so I knew exactly when I ovulated, and my u/s was accurate within 2 days, but with my son, the u/s had him measuring 5 days ahead.

On about.com they have a pregnancy due date calculator that helped me.  It will give you your due date and show you a weekley guide of what your baby looks like as well as what you and your baby are going through.  It is very interesting.  Here is the link.  http://pregnancy.about.com/cs/pregnancycalend ar/l/blpregcalc.htm