Test Line Darker Than Control Line?-Know the Truth Behind It! 

Written by Maria
Last updated:
Reviewed by Margaret

The article has been reviewed by medical expert Margaret Dogwood, BSN, RN

If you’re taking a pregnancy test and notice that the test line is darker than the control line, you might be wondering what this means. In this article, we’ll explore the reasons behind this phenomenon and what it could indicate about your pregnancy. To create this guide, we consulted with medical professionals and researched scientific literature to provide you with accurate information and helpful insights. We understand that pregnancy tests can be confusing, and we hope this article can help alleviate any concerns you may have. So let’s start!

How Pregnancy Test Works?

Human chorionic gonadotropin (hCG) is a hormone that is produced when a fertilized egg successfully implants in a woman’s urine. To put it simply, this hormone is released after conception, usually 10 to 15 days after a woman conceives.

A pregnancy test is an effective way to confirm your pregnancy. According to the U.S. Department of Health and Human Services, the in-home pregnancy test exhibits 99% accuracy.

Pregnancy test strips contain antibodies that detect the presence of hCG hormone. So when you take a pregnancy test, the strip looks for the evidence of hCG hormone. 

To facilitate users, these test strips contain a window that shows results. One line is a reference line that ensures that the test is successfully carried out. This line has nothing to do with hCG detection. 

The second line is your pregnancy line whose presence indicates that you are pregnant. Let’s learn about pregnancy lines in detail

Pregnancy Test Lines; Control line & Test Line

To accurately interpret your pregnancy test results, you should be acquainted with the meaning of two lines displayed on the strip window. The line that would appear first is called the control line. This line is an indication that the test is working properly. 

This line is usually darker and appears immediately after you soak the tip of the pregnancy strip in urine. On the other hand, the second line, which is termed the test line, is an actual pregnancy test line that implies a positive pregnancy. 

Why Your Test Line is Darker than the Control Line?

So far you know if only one line appears, it shows you are not pregnant. However, two lines indicate you are pregnant. But what if you sneak into the results and notice that the test line is darker than the control line? 

In such a case, we would recommend you sit back, relax, and accept our congratulations, because yes, you are pregnant. Any line in the testing window, no matter fainter or darker than the test line indicates a positive pregnancy. 

As the test line is directly related to hCG hormone, a darker test line means you have a high concentration of hCG hormone. A darker test line means you are further along than assumed.

However, there is more than just a positive pregnancy. 

If you have a high concentration of hCG hormone, as is evident by a darker test line, it can be an indication of a couple of other things within pregnancy.

Reasons if Test Line is Darker Than the Control Line

Let’s look at all the possible reasons for a high concentration of the hCG hormone

Positive Pregnancy

The most common reason for a darker test line is a positive pregnancy. A pregnant woman contains a hCG hormone which is detected by the test strip and if the hormone is in high concentration, the test line would be darker than the control line.

However, when this pregnancy test is taken holds considerable importance. For instance, the hCG hormone is usually in small concentration right after pregnancy and increases week by week. 

The amount of hCG hormone in the first trimester is exceptionally high, usually 49%

Therefore, it is common to have a darker test line in the first trimester. Women mostly take a pregnancy test after they miss periods, so let’s discuss hCG levels in the initial weeks of pregnancy.

  • At 4 Weeks

This is a period of early pregnancy; the embryo implants into the uterus and the placenta starts producing the hCG hormone. The concentration of hCG is extremely low as it just begins producing. 

Therefore it is recommended to undergo testing a week after missing periods or use a testing kit with high hCG sensitivity, such as “First Response ” can detect hCG concentration as low as 6.5 mIU/mL. 

If your test line is darker in this stage, still you need not worry as some women contain high concentration even in the first week after conception.

  • At 5 Weeks

Women mostly go after pregnancy tests on missing their period’s date and it is also the best time to get accurate results. The reason is that your hCG hormone level continues to increase during this stage and gets to an extent where it can easily be detected.

It is completely normal to see a darker test line during this stage because hCG usually gets doubled every 2 to 3 days during the first few weeks of the pregnancy.

  • At 6 Weeks

This is a time when an ultrasound machine can easily hear the beats of an embryo. Therefore, if you notice darker test lines on repetitive attempts, you can consider medical tests, just to be sure. 

  • At 7 Weeks

If you are taking your pregnancy test at this stage, your test line is most likely to be darker as this is the peak time of hCG production. After 6 months, hCG gets doubled after every 4 days and starts declining towards the due date.

It would be best in your interest to take your first prenatal appointment and underground ultrasound test to ensure the healthy growth of your baby.

Multiple Pregnancy

Though high hCG concentration is quite normal in most cases, this could be an indication of multiple pregnancy. The high amount of hCG might be coming from twins or triplets, which is making the test line darker. 

If you are having twins, the hCG level will be exceptionally high during 4 to 5 weeks of pregnancy. Additionally, you would have a heavy flow during your last periods after pregnancy. Therefore, it is recommended to get an ultrasound as it is the only way to confirm multiple pregnancies.

Other Factors

In rare cases, a darker test line comes from external factors, such as improper testing, medication, etc.

  • Faulty Test

If your test line is darker than the control line, it may be an indicator of a faulty test. A faulty test can occur due to several reasons, such as;

  • Improper handling of the test kit
  • Too much or not enough urine on the strip
  • Antibiotics do not work properly
  • Using an expired pregnancy test strip
  • Improper storage of pregnancy test kit\
  • Late-night testing

Whatever the cause is, if you are carrying out a faulty test, it might faint or darken the test line, leading to inaccurate results.

  • Medication

Sometimes, a darker test line may come from the usage of some medication. If you are taking any medication that contains some level of hCG hormone, you are most likely to get a darker test line, leading to a false positive. 

Especially if you are undergoing fertility treatment, it could be an indication of a darker test line.

  • Test Sensitivity

In some cases, the darker test line comes from the high sensitivity of the pregnancy test. If you are using a brand that contains a high sensitivity of hCG hormone, your test line would be darker even if the concentration of hormone is moderate or even, in low concentration.

As technology is advancing at a rapid pace, you would mostly encounter such a situation as brands are increasing the hCG sensitivity of their test kits to confirm pregnancy as early as possible.

How to Carry Out Pregnancy Test: Best Practices

No matter, if this is a positive or a negative experience for you, waiting for the pregnancy test results is nerve-wracking. When the first line appears on the window, your eyes get all screwy waiting for the next line.

Then a second line appears and you look twice and thrice to confirm your pregnancy. However, a darker or a much faint test line might get on your nerves. You may end up taking multiple tests or trying different brands.

Instead of this hustle-bustle, why not follow the instructions mentioned on the test and proceed accordingly to avoid any sort of confusion?

We will walk you through some helpful tips to prevent darer testing lines coming from a faulty test. Following them will ensure accurate testing and reliable results.

Follow the Recommended Time Frame

After taking the test, you don’t have to wait a whole day to get the results. It is always wise to carefully read the instructions on the pregnancy test and follow the time frame within which you have visualized the results.

Usually, the recommended time frame is 10 minutes. So do not exceed this time as it can alter the results. 

Wait Till Morning

It is recommended to take a test right after waking up in the morning. The reason is that if you are pregnant, hCG will build up in your urine during the night and will peak in the morning. Therefore, checking your pregnancy in the early morning will yield accurate results.

Dip Test in a Cup

Some women make the mistake of holding a test strip under their urine stream. This method is error-prone and messy. You might not get the required amount of urine on the test strip. 

Instead, collect your urine in a small plastic cup and soak your test strip in the urine for the recommended time to get accurate results.

Take Medical Test if You are on Medication

Medication and fertility treatment, as mentioned above can affect the test results. Therefore, it is always wise to undergo a medical test to confirm your pregnancy. Some drugs might contain high amounts of hCG leading to a fake positive indication of pregnancy.

Therefore, seek medical help and disclose any medications or treatments to a healthcare provider before taking a pregnancy test to ensure accurate results.

Test A Week After Missed Periods

The best time to test your pregnancy is a week after missing your first period. This is a time when the hCG level is high and gets easily detected. However, if you can not wait, checking it two weeks after your sexual intercourse would be helpful. However, it is wise to wait till you miss your period date.

Repeat testing

If you are unsure if a darker test line is coming from a high hCG level or a faulty procedure, it would be best to repeat the test after a couple of days. Following the right procedure is the key.

If you are still having a darker test line, it would surely indicate a high hCG level.

However, you can seek medical assistance to confirm the reason behind the high concentration of hCG.

Interpreting Different Brands of Pregnancy Tests

As mentioned earlier, some pregnancy test brands have high levels of sensitivity, leading to a darker test line. For instance, 

First Response

This is one of the popular brands of pregnancy tests that use a pink dye to indicate the results. The test is highly sensitive and can detect hCG levels as low as 6.5 mIU/mL. So if your test line is darker, it does not necessarily indicate high hCG as high sensitivity can detect even a minute amount of hCG in your body, leading to a darker line.

Clear Blue

This pregnancy test contains a color-changing tip that turns from pink to white when correctly used. However, its sensitivity is 25 mIU/mL, which is less than the previously mentioned brand. Therefore, if you found a darker test line while using this brand’s testing kit, your hCG might be high due to any of the reasons mentioned above.

There are many other brands that you can consider for your pregnancy test. Some would use a digital display, others would leverage pink or blue dye to confirm your pregnancy. Therefore, invest in a good quality testing kit and follow the instructions mentioned by the manufacturer to avoid inaccuracy.

Final Words

Pregnancy is both exciting and nerve-wracking, but everything depends on the results. Once you miss your periods or get any other pregnancy signs, the first thing you would most likely go for is an in-house pregnancy test. 

Make sure the testing kit you opt for is of a reliable brand and check its expiry date. Once you follow the right procedure, the primary window would either show one line (no pregnancy) or two lines (positive pregnancy). 

However, if you notice the test line is a bit on the darker side, there is nothing to worry about. No matter how dark or light your testing line is, you are still pregnant.

It is just an indication of high hCG which can either indicate normal pregnancy or multiple pregnancy. Additionally, it can come from faulty tests or drug usage.

Therefore, we recommend visiting your healthcare provider to know if there is any reason behind the high level of hCG. Following the right testing procedure, using a good quality testing kit, and interpreting the results accurately can timely let you know about this cute addition to your family. 

This will help you start parental care to ensure a seamless journey with a little angel in your belly.

Photo of author
Maria Gonzales, M.Ed., expert in child development and founder of mamallove.com, merges academic insights from Michigan State University with real-life parenting wisdom. Certified in Precision Nutrition and Child Development, she offers invaluable advice on nutrition, communication, and education for parents and parents-to-be.

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