Trimesters
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| Thu, 05-24-2007 - 9:29am |
Trimesters: When does each one begin?
By definition, the word ‘trimester’ divides a time into three equal parts. However, pregnancy is not neatly divisible by three. If you calculate from the last menstrual period (LMP) with a 28-day cycle, a pregnancy lasts 40 weeks or 10 lunar months. If you calculate from probable conception, again based on a 28-day cycle, you are left with a gestational period of 38 weeks. Neither of these is divisible by three. As a result, you get somewhere in between 12 2/3 weeks and 13 1/3 weeks. Conventionally, it is common to say that the first trimester ends at 12 weeks (12 weeks from the first day of the last period). The second trimester proceeds from 12 to 28 weeks and the third trimester extends from 28 to 40 weeks.

"By definition, the word ‘trimester’ divides a time into three equal parts."
But WHY does the 2T have to be 3 weeks longer! I swear it is a conspiracy against all of us preggos!! lol
 
Ha ha!