If I visit a pregnancy calculator such as this one, and enter May 25th 2010 as the first date of the last menstrual period, it says (as of today) that the gestational age is 7 weeks. However, today (July 13th) is exactly 7 weeks past May 25th.
How could the baby have been conceived on May 25th 2010 if my wife was menstruating on that date (and continued to menstruate for about a week past this date)?
asked 14 Jul '10, 06:55
that is because of the calculation that is used.
If you say that a pregnancy is 40 weeks (or 280 days), this is from the date of the last period till the birth.
But the actual conception happens in week 2 of the pregnancy if you count it like this.
Check this article: http://www.whattoexpect.com/pregnancy/week-by-week/weeks-1-and-2.aspx
answered 14 Jul '10, 10:47
Also most calculators presume that women have a 28 day cycle and ovulate on day 14, this as we know is not allways the case. I for example can range from a 28 - 34 day cycle and only have a 10 day luetal phase, so when i go for a dating scan my EDD is normally put back by at least 10 days.
answered 16 Jul '10, 07:02