The short explanation
A pregnancy test detects a hormone that the body starts making after a fertilised egg implants in the womb, which usually happens several days after conception. Most home urine tests become reliable from about the first day of a missed period, and some sensitive ones can pick it up a few days earlier, though early testing gives more false negatives. Testing within a week or so of sex is usually too early. A blood test at a lab can detect lower hormone levels than a urine test and gives a number. It is useful if urine tests are unclear, if you have irregular periods, after fertility treatment, or when doctors need to follow how the level is changing, for example if there is pain or bleeding.
What depends on your situation
The parts of this that change from woman to woman. Uncertainty is stated, not hidden.
- If your cycles are irregular, count about three weeks from the sex that might have led to pregnancy, rather than relying on period dates.
- If you had unprotected sex in the last few days and do not want to be pregnant, emergency contraception works best when used soon; ask a pharmacist or doctor quickly.
- Use first-morning urine and follow the leaflet timing exactly.
What this answer cannot determine
The boundary of online education. These need a clinician who can see you.
- This cannot tell you whether you are pregnant. Only a correctly timed test can show that.
Questions for your clinician
Take these with you. You can add any of them to an appointment card.
- When is the best time for me to test given my cycle?
- Would a blood test be more useful for me?
- If the test is negative and my period does not come, what next?
- What should I do now if I may be pregnant?
When to seek help
Clinician-approved guidance for this topic. When in doubt, being seen is never the wrong choice.
Emergency — call 112 now
- Call 112 or go to the nearest emergency department if, with a possible pregnancy, you have severe one-sided belly pain, shoulder-tip pain, fainting or heavy bleeding.
Book an appointment soon
- See a clinician within a few days if your test results are unclear or your period is late with negative tests.
Raise it at a routine appointment
- Book a routine visit to plan antenatal care once a pregnancy is confirmed.
Sources
The evidence this explanation is built on.
- Pregnancy MedlinePlus (NIH)
- Prenatal care MedlinePlus (NIH)
- Ectopic pregnancy MedlinePlus (NIH)
Who wrote and reviewed this
Every AskHer answer names its author. A clinically reviewed answer also names the clinician who signed it off — if no clinician is named below, it has not been clinically reviewed.
- Author
- AskHer Editorial (AI-assisted draft) AskHer's editorial team — not an individual clinician Works in English, தமிழ், हिन्दी
- Clinical reviewer
- Nobody yet No clinician has signed this answer off, and no person on the editorial team has read it yet. That is what the “Written with AI assistance” label means. It is queued for an editor to read, and then for a clinician who works in this area. The sources it was drafted against are listed above.
- Review status
- Written with AI assistance — not yet reviewed by a person
- Last reviewed
- Not yet reviewed by a person
- Version
- 1
Correction history
Substantive changes are listed, not quietly edited away.
No corrections have been made since this answer was first published.
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