The most obvious sign of pregnancy is a missed period. This occurs 15 days after ovulation. At this stage, a pregnancy test will give a reliable result. Pregnancy tests measure the levels of human chorionic gonadotropin (hCG) in the blood or the urine. hCG is produced once the fertilised egg attaches to the wall of the uterus. Once implantation has occurred, levels of hCG double every two to three days, until they reach detectable levels, approximately two weeks after ovulation.
Read more about the subtle signs of pregnancy here.