Pregnancy tests detect the presence of a hormone called human chorionic gonadotropin (hCG) in a woman's urine or blood. This hormone is produced by the placenta shortly after a fertilised egg attaches to the uterine lining.

Most over-the-counter urine pregnancy tests can be taken as early as the first day of a missed period. However, some tests claim to detect pregnancy even earlier. Blood tests, which are done in a healthcare setting, can detect pregnancy sooner, often within a week of conception.

Home pregnancy tests are generally quite accurate when used correctly. However, their accuracy can vary depending on factors such as when they are taken and how well the instructions are followed. False negatives can occur if you test too early, and false positives are rare but possible.

There are two main types of pregnancy tests: urine tests and blood tests. Urine tests are typically taken at home and are available over-the-counter. Blood tests are conducted in a healthcare setting and are usually more sensitive and accurate, capable of detecting pregnancy at an earlier stage.

If you get a positive result on a home pregnancy test, it's advisable to consult with a healthcare professional to confirm the pregnancy and discuss your options and next steps.