Should a pregnancy test get darker everyday

By Lindsay Meisel | Published Dec 10, 2019 | Last updated Sep 17, 2020 ✓ Fact checked
Medically reviewed by Rachel Liberto, RN on December 13, 2019

When you get only a faint line on a pregnancy test, it can be hard to believe you’re truly pregnant. But even when the line is very faint, it’s still a reliable confirmation of pregnancy.

Not convinced? This post will explain the science behind how pregnancy tests work to reassure you that a faint line on a pregnancy test really means you’re pregnant.

How pregnancy tests work

Once the embryo implants in the uterine lining, it begins to product the hormone hCG. Pregnancy tests detect the presence of this hormone in your urine.

Immediately after implantation, hCG levels are very low. In a healthy pregnancy, they will double every two to three days.

A home pregnancy test does not provide a precise measurement of hCG levels, but the darkness of the line does correspond to relative hCG concentration. In other words, if you take a pregnancy test every few days during early pregnancy, the line should get progressively darker as hCG levels increase.

Is a faint line still positive?

When it comes to pregnancy tests, any line is considered a positive result—even a faint line on a pregnancy test is a positive! That’s because a pregnancy test only turn positive when hCG is present in your urine.

In most cases, hCG is not present in your urine unless you are pregnant. However, there are a few exceptions to this rule:

• Fertility medication: Injections of hCG are a common fertility treatment. Depending on the dosage of the injection, you may need to wait 7 – 14 days before a home pregnancy test would be accurate.
• Rare cancers: Rare cancers can produce hCG, leading to a false positive result on a pregnancy test.
• Indent or evaporation lines: While not a true false positive, certain pregnancy test features can sometimes look similar to a positive pregnancy test. In these cases, the second line is usually gray as opposed to pink

What does a faint line on a pregnancy test mean?

Usually, a faint line on a pregnancy test simply means that you are pregnant. If you’re testing within a few days before or after your period is due, you are very early in pregnancy. Your hCG levels have not increased enough to create a dark line on a pregnancy test.

But what if you’re five or more weeks pregnant and still get a very faint line on a pregnancy test? There are a few other possible explanations for this:

• Diluted urine: If you’ve had a lot of liquids shortly before taking the pregnancy test, the hCG in your urine may be diluted. This could cause a pregnancy test to appear lighter.
• The hook effect: As you progress in your pregnancy and hCG levels increase, a different form of hCG becomes dominant in your urine. Pregnancy tests are designed to detect “intact hCG”, but after the first few weeks of pregnancy, hCG-βCF becomes predominant and this can dilute the intact hCG.
• Chemical pregnancy/miscarriage: During a miscarriage, hCG levels eventually begin to fall. As hCG levels fall, the second line on your pregnancy tests would become more faint.
• Ectopic pregnancy: If the embryo implants outside the uterus, hCG levels will not rise as quickly or as high as with normal implantation. This could lead to faint lines on a pregnancy test.

Can you see a faint line on a negative pregnancy test?

Sometimes you might see a faint line on a negative pregnancy test, but this line does not look the same as a true positive result. There are two cases where you might see a faint second line when you are not pregnant:

1. Evaporation line: This is a faint line that appears on a pregnancy test after the ink has dried. Pregnancy tests are designed to be read during a three to five minute window during which the ink is still wet.
2. Indent line: If you see a very faint second line with no color at all, this may be an indent line. Pregnancy tests contain indentations for the ink to pool. On a positive test, the colored ink pools in the second indentation. If you can make out a faint second line with no color, you are likely seeing the indentation itself.

Does darkness of pregnancy test matter?

Yes and no. Pregnancy tests detect the levels of hCG in your urine. In a healthy pregnancy, hCG levels double every 2 – 3 days.

This means that if you take your first pregnancy test very early in pregnancy and get a faint positive, you should expect to get darker positives if you test over the next few days/weeks.

But if you take a pregnancy test two days in a row, or even multiple times in one day, you won’t necessarily see a darker test line with each subsequent test. The amount of hCG in your body is increasing, but the amount in your urine may fluctuate based on your hydration.

And later in pregnancy, due to the hook effect, your pregnancy tests may start getting lighter even though your total hCG levels are very high. The time during pregnancy when this effect begins depends on a variety of factors and is not the same across all women or all pregnancies.

Read more about pregnancy tests

Late period, negative pregnancy test?

How to decide when to take a pregnancy test

Our guide to the best pregnancy tests

How to avoid a false negative pregnancy test

By Lindsay Meisel | Dec 10, 2019

Lindsay Meisel

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