Pregnancy Tests

Although Human chorionic gonadotrophin (hCG) is a sure sign of pregnancy, it can still be present after a miscarriage or termination for up to eight weeks, or for about four weeks after giving birth. Fertility drugs can also cause ‘false positive' pregnancy test results. Alcohol, painkillers, antibiotics and oral contraceptives do not affect pregnancy tests. More info here
Always test a ‘mid-stream urine' sample - this means to pass some urine into the toilet first, then collect the urine sample for testing, then finish passing urine into the toilet.
Best time to test is first thing in the morning when hCG is at the highest concentration in the urine.
If the test is negative or inconclusive, even though a period has been missed, make sure the instructions have been followed correctly, and repeat the test according to the manufacturer's instructions. If the second test is negative and you still have not had your period, see your doctor.