She doesn't have to do anything usually.

Semen and sperm are designed so that at least some semen stays inside the woman, even if it appears that the majority seems to run down her legs! Hell that's one of the reasons there's so much sperm ejaculated at any one time.

I suppose it's possible that women's instinct (in most cases) to lie and cuddle after sex may have evolved due to pregnancy being more likely to occur under these circumstances, but that's just speculation on my part.

If it was as easy as 'stand up directly after sex' there wouldn't be all the thousands of unplanned pregnancies would there?

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Fruit flies like a banana"

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