How soo can a woman realize that she has conceived?

In some cases, she can get a good idea almost immediately. Some women experience a sudden pain called "mittelschmertz", which is German for "mid-cycle pain", which signals the moment of ovulation. If you feel this very soon after unprotected intercourse, there's a very high chance that you will be pregnant within the next day or so.

If you don't experience mittelschmertz, then your first symptom of pregnancy is likely to be missing your period, at about 2-3 weeks. Some midwives and nurses learn to recognize a "glow" to your skin which may signal the first hormones of pregnancy; these women are astonishingly accurate at the 1-2 week mark, even before you've missed that period.