- Jan 3, 2018
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Conception can take place as quickly as 3 minutes after ejaculation (if there's an egg waiting), or can take up to 5 days, depending on ovulation.Most sperm haven't even entered the cervix 2 hours after sex. It takes a couple days for conception to occur
Implantation of the fertilised egg to the uterine wall usually occurs 5-10 days after fertilisation\conception.
This is when HCG (human chorionic gonadotropin) starts being produced, which is what's detected by pregnancy tests.
Which is why, when testing for pregnancy, they advise to wait for at least 21 days, after unprotected sex.
So you're quite correct about the length of time until testing becomes viable, but conception can actually be much quicker than you expect.