Expert: Shan Yi Sheng - 1/28/2009

Question
When does the fertilization occur? From the next day of 1st missed period? or From the next day after having sex?


Answer
Dear Sweety,

A woman's monthly cycle is measured from the first day of her menstrual period until the first day of her next period. On average, a woman's cycle normally is between 28-32 days, but some women may have much shorter cycles or much longer ones.  Most women ovulate anywhere between Day 11 - Day 21 of their cycle, counting from the first day of the LMP. This is what many refer to as the "fertile time" of a woman's cycle, because sexual intercourse during this time increases the chance of pregnancy. But ovulation can also occur at various times during a cycle, and may occur on a different day each month.

The spermcell could live 3 to 7 days in the female body.
So in the fertile period from day 11 of the female cycle fertilization can take place, even if having sex took place 3 to 7 days earlier.

This is more complicated than most people think.


You miss your period when fertilization has already occurred and pregnancy hormones cause stopping periods.

Hope this answers your question.
bests, dr Shan

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