If you are using ovulation test strips, a strong positive test may last for about 12h, and the exact time is not very precise, which is closely related to the concentration of luteinizing hormone LH in the body. Luteinizing hormone reaches its highest level on the day of ovulation, and then begins to decline, ovulation test paper will go through the weak positive-positive-strong positive-weak positive changes. A strong positive ovulation test paper is considered to be the start of ovulation, which is when the chances of pregnancy are higher during sex. In order to increase the rate of conception, the woman can put a pillow under her buttocks during sex, and lie down for a while after sex, which will help the semen fully enter the uterine cavity and help increase the rate of conception. Ten days after sex, you can do a serum human chorionic gonadotropin test.