Home pregnancy tests: when to test, faint lines and unclear results

A home pregnancy test looks for one thing: a hormone called human chorionic gonadotrophin (hCG) in your pee. Your body starts making hCG around 6 days after fertilisation, according to the NHS, and the amount builds up quickly with each day of pregnancy. So timing matters, and a test taken a few days too early can say “not pregnant” when you are.

The earliest day a result is reliable

The NHS says most tests can be used from the first day of a missed period. If you don’t know when your period is due, it suggests testing at least 21 days after you last had unprotected sex.

Some very sensitive tests can be used before a missed period. The US Office on Women’s Health (OWH) notes that some say they work 4 or 5 days before your period, though even these claim their best accuracy only after the day it was due.

The wait is about implantation. A fertilised egg has to implant in the womb before hCG is made, which OWH says usually happens about 10 days after conception. It adds that in up to 10% of women, implantation doesn’t happen until after the first day of a missed period.

The US Food and Drug Administration (FDA) puts it in cycle terms: with a 28 day cycle, hCG can be detected in urine 12 to 15 days after ovulation. It also says 10 to 20 pregnant women out of every 100 will not detect their pregnancy on the first day of their missed period, partly because periods are often irregular and due dates are easy to miscalculate.

If your periods are irregular

Advice on timing differs between countries. The NHS suggests testing at least 21 days after unprotected sex. In the US, OWH suggests counting 36 days from the start of your last period, or four weeks from the time you had sex. By then, hCG should be high enough to show up if you’re pregnant.

Getting the clearest result

Brands differ, so read the leaflet in the box and follow it closely. Most tests ask you to hold a stick in your urine stream or dip it into a cup of urine. A few things help:

• Check the expiry date before you use it.
• Use a timer. MedlinePlus, the US National Library of Medicine’s health site, says guessing the timing can make the result less accurate.
• Don’t drink large amounts of fluid beforehand. It can dilute the hCG in your urine so it doesn’t show up.
• Look for the control line or symbol. If it doesn’t appear, the test didn’t work and you’ll need another one.

Advice on time of day varies. The FDA and MedlinePlus suggest first morning urine, because it usually has more hCG than urine later in the day. The NHS says a sample collected at any time of day is fine, and it doesn’t have to be the morning.

So does reading time. Most brands ask you to wait around 2 minutes, OWH says, but research suggests waiting 10 minutes gives the most accurate result. Go by the time printed on your own test’s leaflet.

Faint lines and results that are hard to read

Faint lines cause most of the squinting. OWH answers them plainly: “No matter how faint the line or plus sign, if you see it, you are most likely pregnant.” It adds that a faint line can mean you’re early in pregnancy and your hCG levels are still low.

A home test answers a yes-or-no question. The FDA calls it a qualitative test: it shows whether hCG is raised, but not how much there is. Only a quantitative blood test, done by a doctor, measures the exact amount.

If you can’t tell either way, take another test in a few days. If a test says you’re pregnant, OWH suggests seeing your doctor for another test to confirm it and to talk about next steps. In the UK, you can refer yourself for NHS pregnancy care with a midwife.

When the test says no but your period hasn’t come

A positive result is almost certainly correct, the NHS says, while a negative one is less reliable. Testing too early is one common reason: the placenta may not yet have made enough hCG for the test to detect, as the FDA explains.

If you get a negative result and still think you’re pregnant, wait a few days and test again. Sources differ slightly on how long. The NHS and OWH say a few days, and MedlinePlus suggests repeating the test a week after the first one. In the UK, speak to your GP if a second test is negative but your period still hasn’t arrived. In the US, OWH suggests calling your doctor if more tests say you’re not pregnant but you think you are. A doctor can also do a blood test.

Things that can affect the result

Medicines that contain hCG, including certain fertility medicines, can give a false positive. If you’re taking medicine to help you get pregnant, OWH suggests seeing your doctor for a pregnancy test.

Contraception doesn’t stop a test working. The NHS says the hormones in methods like the pill won’t affect the result, and most other medicines, antibiotics included, don’t either. Since no method of contraception is completely effective, take a test if you think you might be pregnant.

A positive test, then bleeding

Early miscarriages are very common. Many happen before a missed period, or before a positive test has confirmed the pregnancy, according to the Royal College of Obstetricians and Gynaecologists (RCOG).

If you’ve had a positive test and then notice light bleeding or spotting, the NHS advises getting urgent medical help. Call your maternity unit if you have the number, or an early pregnancy unit if you’re less than 20 weeks pregnant. If you can’t reach either, call NHS 111. In the US, ACOG’s advice is to report bleeding and pelvic pain to your ob-gyn or another health care professional.

Call 999 (UK) or 911 (US), or your local emergency number, if the bleeding is heavy (soaking a period pad soon after putting it on), or you also have severe tummy pain, pain in your shoulder, or feel sick, faint or dizzy.

After a miscarriage, you’ll usually be asked to do a home urine pregnancy test three weeks later. If it’s still positive, contact your healthcare professional or the early pregnancy unit (EPU). Contact them too if you feel unwell at any time, even if the test is negative.

In the days afterwards, the RCOG advises getting medical advice from your GP, early pregnancy assessment service or the hospital where you had your care, or calling NHS 111, if you have heavy or prolonged bleeding, smelly vaginal discharge, tummy pain that painkillers don’t relieve, nausea and vomiting, or feel unwell. These can be signs of an infection, or that some of the pregnancy is still in the womb. Call 999 or go to A&E if you are bleeding heavily, have severe pain or feel very unwell.

Signs of an ectopic pregnancy

An ectopic pregnancy implants outside the womb, usually in one of the fallopian tubes. It doesn’t always cause symptoms. When it does, the NHS says they tend to develop between the 4th and 12th week of pregnancy, and can include a combination of:

• tummy pain low down on one side
• vaginal bleeding or a brown watery discharge
• pain in the tip of your shoulder

If you might be pregnant and have these symptoms, contact your GP or NHS 111 in the UK, even without a positive test. In the US, contact your ob-gyn or doctor.

Call 999 now (UK) or 911 (US), or your local emergency number, if you could be pregnant and have sudden, severe tummy pain, pain in your shoulder, or feel weak, very dizzy or faint. A fallopian tube can burst (rupture), and that needs treatment straight away.

What to do after a result

A positive result can bring relief, worry or something more mixed. If you plan to continue the pregnancy, contact your GP or midwife (UK) or your doctor (US) to start care. If you’re not sure, you can talk through your options confidentially with a healthcare professional. In the UK, sexual health services and, for under-25s, Brook also offer free tests and confidential advice.

If you test most cycles, a note of test dates and results in Ruva keeps the details to hand when you speak to a GP, midwife or doctor.