If you’re not sure when your next period is due, you can do a pregnancy test 21 days (three weeks) after you last had Sexual activity (unprotected sex). Some very sensitive tests can be used even before you miss a period.
Pregnancy tests check for the presence of the pregnancy hormone, Human Chorionic Gonadotrophin (HCG) in your urine. This can be tested at home.
After you conceive (when the sperm fertilizes the egg), your body begins to produce HCG. Around two weeks after you conceive, there’s enough HCG for most pregnancy tests to detect it.
To conceive, an egg needs to be released from your ovaries (ovulation). Ovulation usually happens about 14 days after the first day of your last period.
An egg lives for about 12-24 hours after it’s released. For you to get pregnant, a sperm must fertilize the egg within this time.
Sperm can live for up to seven days inside your body. This means within a day or so of ovulating, you could conceive.
Around seven days after you conceive, HCG might be noticeable in your urine in very low levels, though this varies from woman to woman. Most tests need a higher level of HCG to give a positive result.
A positive test result is almost correct. If you do a pregnancy test on the first day of your missed period, and it’s positive, it’s probably about two weeks since you conceived. You can use the pregnancy due date calculator to work out when your baby is due.
A negative result is less reliable. If you still think you’re pregnant after a negative result, wait a week and try again or see your GP!
If you are trying to get pregnant, guidance from NICE advises that, for the best chance of success, you should have Sexual activity every two to three days throughout the month. You don’t need to time it to coincide with the days when you ovulate.