Hi Pride, Thanks for the question. Let me explain a bit of the reproductive process so that it will clear any doubts in your mind. In a normal menstrual cycle one ovum is produced and released for fertilization by a sperm. The release usually occurs 14 days before the date of next period and the ovum can be fertilized only for 24-36 hours after release, after which it is lost and there is no chance of pregnancy. If the periods are regular and every 28 days [this is the cycle seen in most women] the ovum is released 14 days prior that is on day 14 after the first day of the last period. So ideally the chances of pregnancy are low till day 13 and after day 16. Unfortunately this does not occur so regularly, so sometimes it releases on day 12 sometimes on day 18 depending upon how the hormones have been in that month. So as doctors, we advice contraception on almost every day except during menstruation and 2-3 days after menstruation. Even then, if the cycles are very regular, chances of pregnancy are very low immediately before the day of the period. But since the process is unpredictable, if period is missed after unprotected sex, the best policy is to do a urine pregnancy test after the missed period [the later the better if you are suspecting that ovulation has occurred late as the conception occurred almost prior to periods]. The best is to do a test 3 weeks after the act of unprotected sex if a period is missed in cases of delayed conception as we call it. Regarding if the period is missed or not: Sometimes women have slight bleeding at the time of periods, even after getting pregnant called implantation bleeding that may be confused with periods. Otherwise most of the time periods are usually missed. I hope I have explained all this process as clearly as possible. Please feel free to ask any more questions that you may have. Thanks for using HCM. Dr. Madhuri Bagde Consultant Obstetrician and Gynecologist