We know ‒ pregnancy testing can be nerve-racking, whether you’re TTC or not.
This is a pretty life-changing pee you’re about to take.
Knowing how pregnancy tests work can help take some of the stress out of the process.
That’s where we come in.
In this pregnancy testing guide, we’re going to take you through all the details ‒ including when to take the test and how to understand the results.
In this article: 📝
- How do pregnancy tests work?
- How soon is considered too early to take a pregnancy test?
- When is the best time to take a pregnancy test?
- How much do pregnancy tests cost?
- Reading your pregnancy test results
- Do pregnancy tests expire?
How do pregnancy tests work?
First up, we’re going to talk about home pregnancy tests ‒ the ones that involve peeing on a highly intelligent stick.
Urine pregnancy tests
Home pregnancy tests are on the hunt for a hormone called hCG.
Everyone has this hormone present in their bodies.
When you’re pregnant, the amount you have of it increases substantially.
So how does the test know hCG is there?
Well, your pee binds to proteins on the test strip called antibodies.
If there is enough hCG in your system, the combination of it and the test’s antibodies produce a positive result.
What do hCG levels mean?
As soon as conception happens (that’s when sperm fertilizes an egg), your hCG levels start to rise.
The job of this hormone is to stimulate a completely healthy cyst (called the corpus luteum) that develops in your ovaries every month in preparation for a possible pregnancy.
If conception occurs, the corpus luteum releases progesterone, the hormone that makes the uterus a hospitable place for a baby to grow.
And the corpus luteum can only do this with the help of hCG.
hCG is measured in milli-international units per milliliter ‒ basically, how much of the hormone is present in each milliliter of liquid.
So if you see this interesting-looking unit ‒ mIU/mL ‒ that’s what it is.
According to the American Pregnancy Association, this is what hCG levels translate to on a pregnancy test:
- Below 5 mlU/mL is considered negative
- Between 6 and 24 mIU/mL is considered a gray area and needs a retest
- Above 25 mIU/mL is considered positive
For the first 4 weeks of pregnancy, hCG doubles every 2.5 days.
Blood pregnancy tests
Another option is to have a blood pregnancy test.
This will be done by a healthcare professional.
And while the process is quite different, the test is looking for the same thing.
You guessed it ‒ hCG.
There are two types of blood tests for pregnancy:
- Qualitative blood tests, which tests for sufficient levels of hCG for pregnancy
- Quantitative blood tests, which test the exact amount of hCG in your blood, making them even more accurate than qualitative blood tests and urine tests.
If you have a positive urine or blood test, your doctor may do a transvaginal ultrasound to confirm the result.
They’ll usually wait until your hCG levels have reached at least 2000 mIU/mL.
That’s around weeks 5 or 6 of pregnancy.
How soon is considered too early to take a pregnancy test?
So how soon is too soon to test for pregnancy?
Conception usually happens shortly after ovulation, around two weeks before your next period is supposed to start.
But even if you’ve successfully conceived, your hCG levels aren’t usually high enough to test until the day of your missed period.
So what happens between conception and the day that your period is due?
This is the infamous Two Week Wait, aka the TWW ‒ and yep, you’re not alone if it feels like an eternity to you.
The “two weeks” refers to the time between ovulation and when you can test to get an accurate result.
Excruciating, we know.
(Head here for tips on how to survive the TWW. And head here if you need support getting through it.)
Why the wait?
Well, the goal here is to ensure you get an accurate result.
If you’re TTC, you may have become well acquainted with your fertile window ‒ the time around ovulation when you are most likely to conceive.
(Luckily, there are tests for this too.)
Your fertile window is the days leading up to and just after the release of an egg from one of your ovaries.
This egg allows one lucky swimmer (out of a pool of enthusiastic sperm) to enter.
And voilà ‒ a fertilized egg.
This fertilized egg (or embryo) travels through the fallopian tube and implants itself in the lining of the uterus.
This process is called implantation, which, depending on your ovulation date, is usually eight to nine days after conception.
Because hCG is produced in the placenta (which starts forming after implantation), it’s only then that hCG levels start to rise.
And it should reach detectable amounts around your next expected period.
Which brings us to our next important question:
When is the best time to take a pregnancy test?
The best time to take a pregnancy test is the day after the first day of your next expected period.
If conception has taken place, your body has enough time to go through fertilization and implantation and build up detectable levels of hCG.
So, if you were expecting your period to start on September 1, and it’s still not here on September 2, then it’s time to take the test.
By this point, there’s a chance that you could be experiencing some very early signs of pregnancy, including fatigue, breast tenderness, and a frequent urge to pee.
And, of course, the famous one ‒ a missed period.
Another thing to know about timing?
Take your pregnancy test first thing in the morning.
An entire night’s worth of no drinking and no peeing means your hCG levels are most concentrated at this time.
Home pregnancy tests are really good at their job ‒ giving an accurate result about 99% of the time.
But there are also times when they can give false results.
The best you can do to avoid this is to follow the instructions on your specific test to the letter.
But even if you do everything exactly as you should, there are times when you can get inaccurate results.
Here’s the lowdown.
It is possible to get a false negative if you are pregnant but not enough hCG has built up in your system by the time you take the test.
If you have taken a pregnancy test too early – say, several days before your next expected period ‒ and got a negative result, it’s a good idea to take another one in a few days to confirm the result.
Here are some other reasons why you might get a negative result and still be pregnant:
Checking the test too early or too late
Every pregnancy test comes with a set of instructions that tells you exactly what to do and how long to wait before reading the results.
(Welcome to the longest three-ish minutes of your life.)
It’s possible that reading the test results too soon can give you a negative result when you are, in fact, pregnant.
And if you wait too long, you might have a false positive on your hands (more on this below).
Testing later in the day
The best time to take a pregnancy test is first thing in the morning when your urine is the most concentrated.
There’s a small chance that taking the test later in the day could make it harder to detect hCG in your system.
The “hook effect”
OK, this is an interesting one ‒ and a rather rare reason to get a false test.
The hook effect happens if you have very high levels of hCG in your system.
Seems like backward logic, we know.
But basically, what happens when there’s an abundance of hCG in your system is those detective antibodies on the test strip get overwhelmed.
So you get a negative result ‒ even though you are actually pregnant.
The hook effect is more likely if you are pregnant with multiples, have had an ectopic pregnancy, or have cancer or other illnesses.
If you think you are pregnant but are getting negative results, it’s a good idea to make an appointment with your doctor.
They may suggest a transvaginal ultrasound to see if you are pregnant or if something else is going on.
An ectopic pregnancy is when an egg implants somewhere other than the lining of the uterus, normally in the fallopian tube.
Unfortunately, this becomes a medical emergency, and it means that the pregnancy won’t be able to continue.
If you’ve had a positive pregnancy test or have early signs of pregnancy, and you notice any of these symptoms, it’s important to check in with your doctor:
- Vaginal bleeding
- Sharp cramps low down in your pelvis, usually on one side
- Pain in your shoulder
- Pain or discomfort when peeing
- Upset stomach
- Dizziness and fatigue
(We know ‒ it’s tricky because a lot of these symptoms can be caused by your normal menstrual cycle. But if you think there’s a chance they could be pregnancy related, it’s best to chat with your healthcare provider.)
There are some rare cases where an ectopic pregnancy can show up as a false negative on a pregnancy test.
If you have a negative pregnancy test but still have one or more symptoms of an ectopic pregnancy, it’s best to get in touch with a doctor ASAP.
As for false positive results, they are less likely but can happen.
(Wow. As if taking a pregnancy test wasn’t stressful enough!)
The main reason for a false positive is that you have higher levels of hCG in your system for other reasons.
If you’ve recently been pregnant, you may still have enough hCG in your body for the test to detect.
Some illnesses can cause high hCG levels, including bowel and liver disease, stomach ulcers, and rarely, ovarian cysts.
Certain medications, including those used for fertility treatments, can lead to a false pregnancy test.
Some drugs for seizures, psychosis, anxiety, and nausea can all interfere with your results, as can some antihistamines and birth control pills.
Important: If you experience early pregnancy loss, that is not the same thing as a false positive test.
It means that you were pregnant.
And you are 100% allowed to take the time you need to heal.
Seek support from your friends, family, and the Peanut community ‒ we have a support group exactly for this purpose.
You may also want to explore talk therapy as an option to navigate this time.
This is grief.
It can be devastating.
And you don’t have to just go on as if nothing happened.
How much do pregnancy tests cost?
Simple tests can be as cheap as a dollar.
And some health centers even give them out for free.
Pregnancy tests come in various shapes and sizes and have different ways of displaying results.
As they get more high-tech, the costs tend to rise.
Very sensitive digital tests, like this one, might be able to give you an accurate result up to six days before your next expected period.
But they do come with a heftier price tag ($20 and up).
Because the TTC experience often means taking more than one test, sometimes within a short space of time, pregnancy tests are often sold in packs of three or more.
Reading your pregnancy test results
Depending on the type of test, a positive test may look like:
Standard, simple, and usually the most affordable option, this type of pregnancy shows two lines if it’s positive and only one if it’s negative.
Pregnancy tests use either pink or blue dyes to show your results.
(The word out there is that the pink dye tests are more accurate ‒ but all pregnancy tests work in the same way, so don’t let this stop you from taking a blue dye test if you have it on hand.)
The first line to appear is called the control line.
It shows you that the pregnancy test is working.
If a second line appears, that’s a positive result.
And what about faint lines on a pregnancy test?
Well, this one’s tricky.
It could be a very early positive result, or it could be something called an evaporation line.
As the name suggests, an evaporation line is a very faint second line from evaporated pee that’s left its mark on the test, rather than a sign that there’s sufficient hCG in your system to give a positive result.
The most common reason for this to happen?
Waiting too long to read the results.
A positive result should show up within 2-3 minutes.
(Read the test directions for exact timing.)
If a line shows up after 3+ minutes, it’s probably an evaporation line.
Another reason for an evaporation line?
The test got wet.
(Pro tip: always store pregnancy tests in a cool, dry place to avoid exposure to moisture.)
The best thing to do if you get either faint lines or what you suspect is an evaporation line?
Test again or visit your doctor.
Some pregnancy tests give you your results in the form of a + or - sign.
First, you’ll see one horizontal line appearing.
In the case of this type of test, that’s the control line.
If a second one appears ‒ a vertical one this time ‒ it’s positive.
Welcome to the world of the digital pregnancy test.
These tests don’t mince words.
“Pregnant” if it’s positive, and “Not Pregnant” if it’s not.
Some very advanced tests, like this one from Clear Blue, even show you how many weeks you might be pregnant.
(Just note that this still needs to be confirmed by a doctor ‒ and the most accurate way they can do this is through an ultrasound.)
Do pregnancy tests expire?
Yep, they do.
And that goes for all types, even the more expensive digital options.
Pregnancy tests work by creating a chemical reaction between antibodies and hCG (if it’s present in sufficient amounts).
And after a while, those antibodies may not be as active as they once were.
As a result, pregnancy tests usually expire somewhere between a year and three years after the date of manufacture.
(You’ll be able to see the expiration date on the box.)
So what happens if you take an expired pregnancy test?
Well, the result might be accurate ‒ but it’s hard to know for sure.
You’re more likely to get a false negative than a false positive result with an expired test.
That’s because the test has become less able to detect hCG.
We say, either way, test again with a test that hasn’t expired yet.
Pregnancy tests that may need more than a second opinion
For millennia, people have come up with methods for pregnancy testing.
Records dating as far back as 1350 show the ancient Egyptians using their own version of a urine test ‒ peeing on wheat and barley seeds over a few days.
If the barley grows ‒ male child.
And if there’s no growth at all, it’s a negative result.
Sadly, we can’t vouch for the accuracy of this creative testing method.
Some other more modern methods that may require similar scrutiny include:
- Salt pregnancy test: Mix your pee with salt. If the concoction comes out “cheesy” or foamy, consider your test positive.
- Toothpaste pregnancy test: Add two tablespoons of white toothpaste to a container. Add your pee. If the toothpaste turns blue and begins to foam, congratulations!
- White vinegar pregnancy test: Place half a cup of vinegar in a container. Add pee. If it changes color, it’s a positive result.
Unfortunately, none of these have scientific backing ‒ but they can be fun if you’d like to try them.
If you think there’s a chance that you might be pregnant, choose from one of the many available at-home test options.
And depending on the result, book an appointment with your doctor.
TTC can be filled with ups and downs ‒ and can feel quite isolating at times.
There are so many others who are where you’re at.
You don’t have to navigate this alone.
Join us on Peanut.
We’re having the conversation.