Answers

2015-10-19T13:29:51+08:00
I think it is because pregnancy can last for 9 months.
For every month there are estimated 4 weeks.
9 months x 4 weeks = 36 weeks
Maybe 40 weeks is the estimated number of weeks pregnancy can last.
Note: 36 weeks is just estimated. I'm sure it is not exact, it is insufficient.
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2015-10-24T17:01:56+08:00

It is because it includes the time of conception up to period wherein the fetus is gaining weight and immunity
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