How Soon Can I Take a Pregnancy Test?
Am I Pregnant?
If you are trying to get pregnant (or even if you just think there is a chance you might be pregnant after having unprotected sex), and you are wondering about the earliest date that you can take a pregnancy test, then there are a number of factors that you need to take into account before you can decide the answer to this.
How Quickly Can I Take a Pregnancy Test and Get an Accurate Result?
Firstly, if your period is already a week late, then you can already take any of the home pregnancy tests that are on the market. You should get an accurate result. I say you "should get"' because obviously there are always exceptions to the rule, and it may depend on how regular your cycles are. The reason most doctors and sources, including AmericanPregnancy.org, recommend waiting until you miss your period is because your body needs time to build human chorionic gonadotropin, more commonly referred to as hCG. HCG is only present in the body when you're pregnant, and that's what most tests test for. It does start building up in your system after fertilization but may not reach sufficient levels to show up on a test until later.
Also, you really need to have regular periods to know when your period is a week late!
So the main factor you need to think about when considering if your period is a week late is:
Do You Know When You Last Ovulated?
If you are monitoring your cycles because you are trying to get pregnant, then you may well know the answer to this question—but if you are not necessarily trying to get pregnant or just not trying and not preventing, then you may well not be aware of when you ovulated.
If you do not know when you ovulated, then you can calculate your estimated ovulation date using your period—although it may not be totally accurate! If you have regular-length cycles, then it is reasonably common to ovulate 14 days before the first day of your period, so you could take that as a rough guess. This may only cover 2/3 of the population though, so may not be that accurate.
So if you think that your period is due on the 20th of the month, then the most common time of ovulation would be around the 6th of the month.
If this sounds a bit confusing and overwhelming, FirstResponse (who produces one of the most sensitive and accurate pregnancy tests) made this handy calculator that helps you estimate when you may have gotten pregnant.
How Soon After Sex Can I Take a Pregnancy Test?
Can and should are two very different verbs here. You can take a test whenever you like. However, if you want accurate results, it's best to take the test at least eight days after you've ovulated. Waiting until 14 days after ovulation is a much better time frame. That means that taking a test immediately after sex won't give you any viable results. Here's why you want to wait:
- Pregnancy Isn't Immediate: Pregnancy doesn't start the moment after you have sex. It can take up to six days for the sperm and egg to join.
- Chemical Pregnancies: According to this study by J. Clin Med Res, "[o]ne of the possible outcomes of the pregnancy test is a biochemical pregnancy; where the initial pregnancy test is positive but does not progress into a clinical pregnancy." A chemical pregnancy is where the sperm and egg meet, but the body naturally miscarries before the person knows they are pregnant. The same study goes on to note that "between 50% and 60% of all first-time pregnancies are thought to end in miscarriage—a large majority of which can be attributed to biochemical pregnancies."
- Test Sensitivity: Not all tests are created equal. Some are much more sensitive (meaning they can register lower amounts of hCG) than others. So, you potentially will get a false positive if you use an insensitive test early when your body hasn't had time to build up hCG. Waiting reduces the chances of this—but doesn't eliminate the chances entirely.
If you do not know when you ovulated but the only thing you know is when you had unprotected sex then you should really wait 18 days for a conclusive result. The reason for this is that you can get pregnant by having sex up to 4 days before ovulation. Then the hCG may not show up on the test until 14 days after that (although the likelihood is it will show up a few days sooner) so that gives a possible timescale of 18 days until you can get a positive result in some cases.
In the majority of situations, however, you should get an accurate result around 14 days after having unprotected sex.
Which Pregnancy Test Is the Most Sensitive?
FirstResponse seems to be the most sensitive according to many clinical tests, including Clin Chem Lab Med's study of the product's efficacy.
There are different pregnancy tests available that pick up the pregnancy hormone, hCG, at different strengths. The most sensitive test picks up hCG levels of about 10 in your urine. Other tests pick up hCG at levels of 20, 25 or 50. So the higher the level of hCG is picked up by the tests, the later you will be able to use that test as the hCG builds up in your system.
That said, not all tests are created equal. J. Am Pharm Assoc. researched the sensitivity and accuracy of over-the-counter pregnancy tests, concluding that "First Response Early Result had an analytical sensitivity of 6.3 mIU/mL, which was estimated to detect greater than 95% of pregnancies on the day of missed period. The sensitivity of Clearblue Easy Earliest Results was 25 mIU/mL, which indicated detection of 80% of pregnancies."
I used the because they balanced price and accuracy, in my experience. Everyone on a forum I used to frequent would recommend these test strips because they were so cheap, showed a positive test pretty early on, and were really sensitive (10mlU). For some reason though, they didn't seem to sell these ones in the shops. They only seemed to be available online, so I would stock up on them so I could use them the next month. The cheapest ones I could find in the shops were much more expensive than these, so it was worth ordering them online. I also learned somewhere along the way that these are the ones that are used by doctors and hospitals. I don't know how true this is, as I don't have any evidence to prove this. One Step pregnancy tests
When Can I Test?
So, the question is, how soon can you use each type of pregnancy test strip? Well, your body would have had to built up certain levels of hCG for the test to show a positive line. The standard levels of hCG differ according to where you look, but wikipedia reports the following levels:
HCG Levels Timeline
Weeks Since Last Missed Period
5 - 50 miU
5 - 426 miU
18 - 7,340 miU
1,080 - 56,500 miU
If you break this down to a more detailed level—based on the pregnancies that I have observed through many friends on a pregnancy forum (not scientific, but you see a lot of stats on there over a year or so)—then you can generally expect tests to show positive according to these levels:
- 10 days past ovulation - should see a faint line on a 10 miU test strip
- 12 days past ovulation - you may see a faint line on a 20 or 25 miU test
- 14 days past ovulation - you may see a positive on a 50 miU test
So this is where it is more important that you know which day you ovulated on last, as there can be a big discrepancy in whether you see a positive or not. Also, of course, some people have a later implantation (the time when the hCG starts to build up), so their levels will not rise until later. Also, bizarrely, there are some people who do not show a positive on a pregnancy test until 6 weeks or later.
So the basic answer is that a lot of pregnancies will show a faint positive (on the right test) between 10-14 days after you ovulated, which would be up to four days before your period is due.
What If My Period Is Already Late?
If your period is already late, then you should be able to test with pretty much any home pregnancy test these days. The most accurate ones are the digital tests that show you a "pregnant" or "not pregnant" in the window to avoid any doubt.
If you get a "not pregnant" or other negative result (but still believe that you might be), wait a week and test again. Or at least wait a few days, especially if you have irregular cycles because that could mean that your ovulation date may be later than you thought.
Also, stress can make your period late (even underlying stress that you don't realize you have), so there is always the chance that worrying about being pregnant is the reason your period has not turned up yet.
Does it automatically mean I'm pregnant if I miss my period?
Not necessarily. There's a litany of reasons why you might miss your period or why it might be a few days late. Dr. Mark Trolice weighs in on the subject, giving understandable, helpful advice.
Ensuring That You Don't Get a False-Positive
What is a false-positive pregnancy test?
A false-positive pregnancy test is exactly what it sounds like: a test gives you a positive result when you're not actually pregnant. False-positives can happen for a number of reasons, including:
- letting the test sit too long before checking it
- an expired test
- being on medications that effect your hCG levels
- experiencing a chemical pregnancy (where you are technically pregnant because implantation has happened but miscarry shortly thereafter)
- a recent miscarriage or abortion (hCG levels take quite some time to dissipate)
- a user error (some test's indicators are not quite clear and/or have confusing instructions)
How common are false-positives?
There doesn't seem to be a lot of research answering this question, so I don't have a clear answer. In "Strips of Hope: Accuracy of Home Pregnancy Tests and New Developments," a study by C. Gnoth and S. Johnson, they found that at-home pregnancy tests were generally far less sensitive than they claimed to be. It perhaps stands to reason then that false-positives wouldn't be all that common. There's not evidence that I could find to back up my claim one way or another.
What should I do if I think I got a false-positive?
- Test again: Try a different brand of test or a different type, and see if you get the same results.
- See a doctor: A doctor's second opinion could help you get more information. Your doctor also might be able to help you explore any other factors that might have led to a false positive.
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
© 2012 Jackie Grant