If you can be sure that you are having intercourse on the third day after the day of ovulation, the likelihood of pregnancy will not be very high, and the likelihood of not getting pregnant is greater than the likelihood of getting pregnant. However, on the day of ovulation when it is not determined by ultrasound that ovulation has occurred, the likelihood of pregnancy is significantly higher. This is because after a woman has ovulated, the egg can survive in the fallopian tube for about 36 hours, which means that the ability to fertilize the egg is very strong within 36 hours, and the ability to fertilize the egg after more than 36 hours will gradually diminish. So, if you are sure that you have ovulated three days ago, more than 72 hours after ovulation, the ability to fertilize is already very weak and pregnancy is unlikely. However, if you have not detected your ovulation through ultrasound, you cannot be sure that you have ovulated on the day of ovulation, because the time of ovulation may also fluctuate to some extent. Therefore, if the time of ovulation is pushed back, the likelihood of pregnancy increases significantly.