Fortunately sperm can survive for two or more days in the cervical mucus, therefore, a precise timing of intercourse is not necessary. Sexual intercourse every two days is adequate to replenish the sperm in the female reproductive tract.

However, if insemination is performed as part of a treatment cycle, then the insemination should be performed within 24 hours after ovulation bypass the cervical mucus.

By nature if a spermatozoon fertilizes an ovum at the outer one third area of a fallopian tube successfully, a zygote will be created and then undergo a series of cell division and embryo growth.

The embryo moves down the fallopian tube toward the uterus, each embryonic cell divides every 14 to 18 hours. Since the embryo is confined within the human eggshell (zona pellucida), the cells become progressively smaller and smaller with each cell division.