Pregnancy tests detect the presence of human chorionic gonadotropin (hCG), a hormone produced by the placenta during pregnancy. While most home pregnancy tests are designed to be used after a missed period, there are some tests that can detect pregnancy earlier, before the period is due.
Early pregnancy tests are more sensitive than standard home pregnancy tests. They can detect hCG levels as low as 10 mIU/mL, compared to 25 mIU/mL for standard tests. This means that early pregnancy tests can detect pregnancy as early as 6-8 days after ovulation, which is about 4-6 days before the expected period.