These dates are all pretty much imaginary dates....The only thing you know for sure is what date you started your last period, which is why they tradititionally start with that date. Some of this stuff predates ultrasounds and other medical tests and that is all they had to work with. The due date is determined by counting weeks, but that is only a statistical average, not definite in your specific case. I don't even think you can necessarily figure out the date of conception after the baby is born because not all pregnancies last the exact same number of days. I can not imagine a reason why it is necessary to know the exact date of conception except in cases where there are different possible fathers. And even then, the dates won't really tell the whole story because you don't necessarily get pregnant the day you have sex. The sperm can live inside the mother for a period of time so the date can be other than what you think.
at 12:28 PM on Mar. 28, 2009