How long can it take to show positive pregnancy test

After getting a negative result on a home pregnancy test, it's fair to conclude that you're not pregnant. However, if you happen to glance back at the test later in the day, you may be surprised to see that a positive line has magically appeared. There are a few reasons why this can happen. However, in most cases, the originally reading of the test, "not pregnant," is typically the correct one.

What Are Evaporation Lines on a Pregnancy Test?

The instructions on most pregnancy tests will advise you to read the results within a certain window of time. This usually ranges between a couple of minutes up until 10 minutes later. If you see a positive result beyond this time frame, you may be left second-guessing the results.

However, the false-positive reading, in this case, is due to something called an evaporation line. Evaporation lines are not indicative of a true positive result.

Evaporation lines happen when the urine that was on the test area starts to dry. The chemical composition of the urine sample changes due to evaporation. As a result, the test may start to display a positive line. After the allotted time has passed, you should discard the pregnancy test to avoid confusion.

If you follow all of the instructions correctly, you may notice a thin, faint test line that appears within a few minutes. It can seem at first that the line is too faint to count, but after 10 minutes, it darkens. There are several possible explanations for this line:

• Chemical pregnancy: When implantation of a fertilized egg happens, hCG is produced, even though that egg may not be viable. Chemical pregnancies are the most common cause of early miscarriage. Without taking a pregnancy test, the miscarriage may easily be mistaken for a regular period.
• Lower sensitivity test:You might need a test with higher sensitivity levels so that you can get accurate results earlier in the pregnancy. Look for "early results" indicated on the test label.
• Too early in your cycle: If you test earlier than 10 to 12 days past ovulation, the hCG hormone may not be high enough to produce more than a very faint line. The best time to test is after your period is late, or 2 weeks after you ovulated.
• Too much fluid: You can dilute your urine sample if you are urinating too frequently or drinking too many liquids—this is why first-morning urine samples are recommended for pregnancy testing.

False Negative Results

While true false negative results are rare, there are multiple reasons why you could get a negative or faint result even if you are actually pregnant, such as not waiting long enough into your cycle to test or testing with diluted urine. Always use a sample from your first-morning urine (which is more likely to have higher concentrations of the pregnancy hormone, hCG).

If you are still unsure about pregnancy test results, wait a few days and test again. If you have any questions or concerns about whether or not you could be pregnant, consult with an OB/GYN.

A Word From Verywell

It can very stressful to see conflicting results on a pregnancy test, such as faint lines or evaporation lines. If you're unsure about your results, retest in a couple of days or talk to your doctor about a follow-up blood test for confirmation. Following the directions on your pregnancy test helps avoid the confusion or disappointment of a false positive.

Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.

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• Accuracy
  • How accurate are home pregnancy tests?
• False-Positive Results
  • What can cause a false-positive pregnancy test result?
• Urine/Blood Tests
  • What tests are done to confirm pregnancy?
• When to See a Doctor
  • When should you see a doctor?
• Related Resources
  • Related Resources - Early Pregnancy Test: How Soon Will a Pregnancy Test Read Positive?

An early pregnancy test can read positive as soon as 11-15 days after conception, 1 day after a missed period

An early pregnancy test can read positive as soon as 11-15 days after conception, 1 day after a missed period. However, more accurate results can be obtained 2 days after a missed period.

A home pregnancy test detects the presence of human chorionic gonadotropin (hCG), which is produced in a pregnant woman. Traces of hCG can be seen in urine 3-4 days after the fertilized egg implants in the uterus, and the amount doubles every 48 hours. When there is enough hCG in the body, a pregnancy test can detect it and produce a positive result. 

If your periods are irregular, however, and your test result is negative, you should repeat a home pregnancy test after 1 week.

How accurate are home pregnancy tests?

Home pregnancy tests are quite reliable and usually 99% accurate. However, it is critical to carefully follow the instructions on the package.

• It is recommended to test your urine in the morning since hCG levels will be at the highest concentration as soon as you wake up.
• You can take the test at any hour of the day, but you need to keep your bladder full for at least 4 hours prior to the test.
• Avoid drinking too much water before the test because it can dilute the hCG levels in your urine.

Here is how the tests work:

• The test kits come with a test stick and a container that is used to collect the urine and transfer a few drops to the test stick.
• If you are pregnant and there is sufficient hCG in your urine, the hCG in your urine reacts with the anti-hCG antibodies present in the test stick and inactivates them.
• As anti-hCG bodies are inactivated, the stick indicates a positive pregnancy test.

What can cause a false-positive pregnancy test result?

In rare cases, a false-positive outcome can be caused by:

• Blood or protein in your urine
• Early miscarriage
• Certain medications, such as tranquilizers, anticonvulsants, hypnotics, and fertility drugs

Other reasons for a false-positive result include:

• Molar pregnancy: Also called a hydatidiform mole, a molar pregnancy is a benign growth that develops abnormally after an egg is fertilized. The placenta develops into an aberrant mass of cells and cysts. In rare cases, an embryo develops but is deformed and will not survive. In some cases, no embryo exists at all. Molar pregnancies can have serious complications and must be treated by a specialist.
• Ectopic pregnancy: Ectopic pregnancy occurs when the fertilized egg implants in a location other than the uterus. In a tubal pregnancy, this occurs in one of the fallopian tubes that connects the ovaries to the uterus. However, the egg can sometimes implant in the abdominal cavity, ovary, or cervix. Because the fertilized egg cannot survive in these locations, the pregnancy cannot progress normally and the growing tissue can harm the mother's internal tissues, resulting in dangerous complications such as life-threatening blood loss. Early treatment of an ectopic pregnancy is critical.
• Chemical pregnancy: Women who get early positive pregnancy test results but then get their period may have a chemical pregnancy. This is a situation in which the fertilized egg implants normally in the uterus, but only long enough to begin generating hCG. The egg then ceases growing for unknown reasons. This form of early miscarriage usually occurs when the fertilized egg has a flaw that prevents it from maturing normally. According to some experts, 20%-30% of all pregnancies end in miscarriage.

QUESTION

What tests are done to confirm pregnancy?

In addition to false-positive results, a home pregnancy test may show a false-negative result, especially if you tested too early or if the kit was defective. 

In order to confirm the results of a home pregnancy test, talk to your doctor to undergo additional tests. Your doctor may order urine or blood tests:

• Urine tests: Urine is tested for the presence of hCG. A diluted sample may produce a false-negative result.
• Blood tests: Blood tests are more sensitive than urine tests and can give an accurate result 9-10 days after conception. Blood test results not only confirm the pregnancy but can also diagnose a potential miscarriage. There are two types.
• Qualitative test: Confirms the presence of the hCG hormone in the blood
• Quantitative test: Measures the amount of hCG present in the blood.
  • Higher hCG levels may indicate a multiple or twin pregnancy
  • Lower hCG levels may indicate a miscarriage
  • Slow rise of hCG levels may indicate an ectopic pregnancy

If pregnancy is confirmed, an abdominal ultrasound can be done to assess the development and health of the fetus.

When should you see a doctor?

Regardless of your pregnancy test results, consult your doctor if you develop any of the following symptoms:

• Dizziness
• Fainting
• Abnormal vaginal bleeding 
• Severe, stabbing pain in the abdomen or on one side of the pelvis
• No period even after multiple negative home pregnancy test results
• Persistent pregnancy symptoms even after negative test results, such as:
  • Nausea
  • Breast tenderness
  • Fatigue

If your home pregnancy test result is positive, you should see your doctor to both confirm the pregnancy and begin prenatal care.

Health News

Medically Reviewed on 3/8/2022

References

Image Source: iStock Images

American Pregnancy Association. What is HCG? https://americanpregnancy.org/getting-pregnant/hcg-levels/

Betz D, Fane K. Human Chorionic Gonadotropin. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022. https://www.ncbi.nlm.nih.gov/books/NBK532950

Memon N. How Soon Will a Pregnancy Test Read Positive? MedicineNet. https://www.medicinenet.com/how_soon_will_a_pregnancy_test_read_positive/article.htm

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