False Negative Pregnancy Test

  • woman-holding-false-negative-pregnancy-test

A false negative pregnancy test is a pregnancy hCG test which is falsely negative, it is negative when in fact you are pregnant and it should be positive. You are pregnant but you have a negative pregnancy test.

False negative versus false positive versus true negative versus true positive pregnancy test.

  • A false negative hCG pregnancy test is a negative pregnancy test when in fact you are pregnant and it should be positive.
  • A false positive hCG pregnancy test  is a positive pregnancy test but you are not pregnant and it should be negative.
  • A true negative pregnancy test is a negative pregnancy test and you are not pregnant
  • A true positive pregnancy test is a positive pregnancy test and you are truly pregnant.
  Pregnant Not Pregnant
Positive Pregnancy Test True Positive False Positive
Negative Pregnancy Test False Negative True Negative

Home Pregnancy Tests

Human Chorionic Gonadotropin (hCG) pregnancy tests or home pregnancy tests determine pregnancy through the detection of the hormone Human Chorionic Gonadotropin (hCG) in a woman's urine. Doctors recommend that you wait until you have missed a period to take a home pregnancy test. If you can not wait that long to find out and you know the day you may have conceived, then the earliest you can take a test would be 14 days from possible conception. Home tests are usually 97% accurate when all instructions are followed correctly and the results are read on time. Some kits come with two tests so that in case you have made a mistake, you may take the home pregnancy tests gain. Learn more about the accuracy of home pregnancy tests in another relevant article.

False Negative hCG Pregnancy Tests And What Causes Them

There are at least several reasons you may get a false negative pregnancy test when in fact you are already pregnant:

  1. You tested too early
  2. The pregnancy test strip has a low sensitivity
  3. The urine is too diluted
  4. There is not enough pregnancy hormone hCG in the urine
  5. The so called "Hook effect" and HERE especially if the hCG is very high like in a molar pregnancy

1.You tested too early and too close to implantation

If you take a home pregnancy test too early when you are already pregnant then you may get a false negative result. This is the major reason for a false negative test. You need a high enough blood and urine hCG pregnancy hormone level to get a positive pregnancy test. Your hCG level both in the blood and the urine will not be high enough until many days after implantation.  

Check this implantation date calculator HERE

CALCULATOR: When to take the pregnancy test

2.The test strips had too low sensitivity

Urine pregnancy test strips vary in their sensitivity. That means they become positive and they can detect the hormone Human Chorionic Gonadotropin (hCG) in your urine at different levels. Test strips and midstream tests and digital tests have different sensitivities which means they show a positive at different amounts of hCG in your urine.  Some HPTs are highly "sensitive" to hCG and detect a relatively low amount of hCG, like 20 mIU/ml. Once the urine shows 20 mIU/ml or higher, the test becomes positive. Other HPTs have a lower sensitivity to hCG and detect hCG only at much higher amounts of hCG, 50 mIU/ml or 100 mIU/ml for example. For example, if your urine has 40 mIU/ml hCGbut you use a strip that detects only 50 mIU/ml hCG then your test will be negative and does not become positive until you reach a higher level. 

3. The urine is too diluted

If your urine is diluted, if for example you drank a lot of liquid, then the concentration of hCG in your urine becomes less and the test may be negative. That is why most manufacturers recommend that you test with more concentrated urine, first morning urine.

It is possible that although your ovum might be fertilized, meaning you may be pregnant, but your body has not started secreting enough Human Chorionic Gonadotropin (hCG) for the test to measure. Your body needs time for the hormone to rise to a high enough level to be detected in a test.

False Negative Pregnancy Test

If the home pregnancy test shows negative results but you still think you could be pregnant, wait a few days and try again. Test in the morning. A negative result can mean that you are not pregnant, that you took the test too early or you took the test wrong, or that the urine is too diluted or the test strip is not sensitive enough. Also, if you have received different answers on multiple pregnancy tests, it is recommended that you get a blood test done to get an accurate answer.

For most pregnant women the urine pregnancy test does not detect enough hCG until 1-2 days before missing the period. And in 1 of 4 pregnant women the home urine pregnancy test does not become positive until after they miss their period.  Most false negative pregnancy tests occur when testing is done too early. You are pregnant but you test negative because there is not enough of the pregnancy hormone hCG in your body and especially your urine to be detected.

Quantitative blood tests and the most sensitive urine tests usually detect hCG shortly after implantation, which can occur anywhere from 6 to 12 days after ovulation. Beta hCG levels rise exponentially in the first two months or so of pregnancy so the earlier the test is performed, the higher the chance of a false negative result. Less sensitive urine tests and qualitative blood tests may not detect pregnancy until three or four days after implantation. Menstruation occurs on average 14 days after ovulation, so the likelihood of a false negative is low once a menstrual period is late.

4. You are overweight and the hCG is too low yet

Women who are overweight and have a high BMI body mass index have lower hCG pregnancy hormone levels. Read more HERE....

5. The Hook effect

A known failure mode for pregnancy detection by urine hCG pregnancy tests occurs when hCG is in large excess and no dilution step is performed to wash the excess hCG variant away. The excess hCG form can simultaneously saturate the fixed, solid-phase antibody and the labelled, soluble antibody, preventing sandwich formation (Figure 1). This "hook effect phenomenon" results in absence of a signal, and thus a false-negative result. The paradoxical decrease in the curve plotting an increased signal with increased concentration of antigen gives the appearance of a hook, hence the name . In urine hCG tests, the hook effect is generally not observed until hCG concentrations reach 1,000,000 mIU/mL, as is seen in gestational trophoblastic disease. However, the "hook effect" can also cause false-negative results in normal pregnancies when an excess of hCG is present. From HERE