Why is due date for birth taken by your last period and not when concieved?

Question

I find this confusing, i just wanted to know why you find out your due date from first day of last period which mine would be 28th july only if im pregnant as its too early to test just now, though if i do fall pregnant then i would had concieved 7th of august. If i am pregnant should i work out the birth from date i concieved (7th aug) or last period, and what is more accurate to determine the due date, from last period or date of conception.

Answer 1

they go by the last period, because there is no way to be sure what day you actually ovulated. generally though, it is 2 weeks after your period started, so they can get a fairly accurate idea of when you are due from that.

Good luck, baby dust to you!

Answer 2

with out sounding gross, you can really become pregnant a few days after you have s*x..  the sperm and egg may take sometimes getting to each other.

So that is why they go by your last period.

Answer 3

no one knows the actual date of conception. You can't even be sure the date of conception because sperm can last for days after s*x. They take into consideration the possible conception date in the 40 weeks you are pregnant. If they did it by conception, you would only be 38 weeks pregnant (give or take). You will have an ultrasound to confirm the accuracy of the due date.  

Answer 4

Doctors calculate based on the LMP because most women (and especially dumb teens) don't know when they got pregnant but they can remember when they had their period. It also means all doctors all over the world are using the same calculating method. Anyway, they will use that data to do a rough guess, unless you are normally on totally long cycles in which case they can calculate it form your ovulation date if you've got BBt charts to prove it. But ultimately, once they do an ultrasound around 20 weeks or later, they change the due date estimation based on the baby's development. So it's not set in stone anyway -- just a pure guess. Only a small minority of babies arrive when they're supposed to ;)

Answer 5

Most women don't know when they ovulate, but they do know when they started their last period.  Doctors have 2 terms that they use "gestational age" and "fetal age".  Gestational age refers to how far along you are in your pregnancy starting from the first day of your last period.  Fetal age refers to the actual age of the fetus starting at conception.  Since it's really hard to pinpoint fetal age, doctors guestimate (that is, make an educated guess) based on several measurements usually taken during your first ultrasound.

Hope this helps clear things up for you.

Answer 6

Because When You Conceive Is Not The Day The Baby Starts Fertilising. It Can Take Up To A WeeK For The Sperm To Fertilise With The Egg. Your Period Happens When That Egg Is Realised. When The Egg Is Realised And Fertilize By The Sperm, It Means The Baby Starts Growning So They Need To Calculate From Then