In general, it takes about 24 hours for sperm and egg to unite, depending on the individual. It usually takes about 1-4 hours for the sperm to travel from the vagina to the fallopian tube, possibly as fast as a few minutes. Fertilization begins when an energized sperm enters the zona pellucida of the oocyte. The fertilized egg usually begins to settle around day 6-7 after fertilization, when the trophoblast cells secrete human chorionic gonadotropin, which doubles every other day if the embryo is well developed; abnormal embryos grow slowly and a biochemical pregnancy or ectopic pregnancy may occur. Pregnancy is a complicated process during which mature eggs, good quality sperm, proper endometrial thickness, and stable estrogen and progesterone are required. You should relax during pregnancy preparation and have intercourse on alternate days during ovulation to have a better chance of getting pregnant. Women with regular periods should go to the hospital promptly when their periods are delayed for 1 week to determine if they are pregnant.