Pregnancy tests detect the presence of Human Chorionic Gonadotropin (HCG) in your urine. Your body produces HCG in response to a fertilised egg attaching itself to the wall of your uterus. This usually takes place around six days after fertilisation. The more sensitive pregnancy tests can detect very low levels of HCG as early as four days before your period is due. However, if you test too early, even with a sensitive test, the level of HCG in your urine may not be high enough to detect. Most pregnancy tests will give up to 99% accuracy if you test around the time your period is due (about two weeks post ovulation).
Ovulation is simply the release of eggs from a womans ovary. Once released and transported to the fallopian tube the egg survives for 12 to 24 hours if not fertilised. This creates a fertility window, which is optimal for conception, lasting up to six days. Ovulation tests help determine your expected ovulation by detecting the presence of luteinising hormone (LH) in your urine. Luteinising hormone is always present in your urine, but increases substantially 24-48 hours prior to ovulation, and triggers the release of the egg from one of your ovaries. Ovulation tests are up to 99% accurate, and once you have received a positive result you will ovulate within the following 24 to 36 hours.
Your basal body temperature is your temperature when you are completely at rest. Most women experience a slight, but measurable, elevation in their basal body temperature when they ovulate. By charting your basal body temperature every day, it is possible to determine if and when ovulation has occured. To do this you need a specifically created basal body thermometer that ranges from 35.6 to 38.4 degrees Celsius.