A positive ultrasound will give you the highest confidence of pregnancy – the other tests are useful, but not 100% reliable. Noticeable fetal movement starts around week 15 or 20, and are a clear reminder of pregnancy for pregnant women. However, non-pregnant women may also feel movement in their abdomen that isn’t caused by pregnancy, so this is not a positive test.
Enlargement of the uterus is also not a totally reliable sign of pregnancy – non-pregnant women can experience uterine hyperplasia (swollen uterus) due to ovarian cysts, uterine fibroids, and certain forms of cancer. Over-the-counter pregnancy tests can also be unreliable, although false positives are far less common than false negatives. A non-pregnant woman might come up with a false-positive pregnancy test if she has taken certain drugs, or has blood in her urine sample.