The evaporation line in pregnancy tests
The evaporation line or ghost line is a faded, colorless streak that appears on a pregnancy test when it is not done correctly.
Taking a pregnancy test can be a nerve-wracking experience, especially when you are unable to interpret the result .
In fact, it may happen that the test shows a light line that is barely visible , where the positive stripe should appear .
So is it a weakly positive pregnancy test or the so-called evaporation line ? Did conception happen or not? Let’s see it together.
What is an evaporation line on a pregnancy test?
The evaporation line or ghost line is a faded, colorless line that appears on the pregnancy test where the positive strip should appear.
The presence of the evaporation line does not indicate pregnancy. This type of strip, in fact, is practically a false positive and appears when the test is not valid . This can happen, for example, because it was read too late or done the wrong way, such as when it gets too wet under the stream of urine.
Evaporation lines only appear on negative tests. A positive test would color in the same spot, erasing the evaporation line.
Consequently, if you see an evaporation line, it means that you are not pregnant or that you tested too soon after ovulation to get a positive result.
What is a low positive pregnancy test?
The pregnancy test works by detecting the amount of beta hCG hormone present in the urine.
In the first few weeks after conception (before menstruation is delayed) beta hCG levels are usually very low. However, they increase rapidly in the first trimester, typically doubling every 48 to 72 hours.
Only urine that contains enough beta hCG causes the second line on the pregnancy test to stain. The control line , on the other hand, must always appear, to guarantee correct functioning of the test.
In early gestation, there may be very little beta hCG in the urine, and the pregnancy test may show a positive faint line .
This second faint line , however, has a similar color to the control line and this distinguishes it from an evaporation line, which is colorless.
How to distinguish a low positive test from an evaporation line test?
A faint line on your pregnancy test may be an evaporation line if:
- appears after more than 10 minutes have passed since the test was performed;
- it is faint and colorless and resembles a water stain;
- it is thinner and not the same color as the control line;
- is not accompanied by the presence of the control line.
A second clear line on the test confirms pregnancy if:
- it is the same color as the control line and has the same thickness, even if it is weak;
- appears within the period specified in the test instructions, which is usually 3-5 minutes;
- the test was performed at least 11 days after ovulation (even better if after 14 days);
- menstruation is late.
How to prevent the evaporation line from appearing?
The evaporation line usually appears when the pregnancy test is not performed according to the instructions on the package .
To prevent the evaporation line from appearing:
- try to urinate into a container (e.g. disposable plastic cup) and immerse the test swab for the duration indicated in the instructions. This way you will avoid unwanted splashes on the test, which could cause abnormal lines to appear;
- check the result within 10 minutes of taking the test. Evaporation lines and false positives tend to appear when more time than indicated has elapsed;
- do not use a pregnancy test that has passed its expiration date ;
- Avoid storing the pregnancy test in very hot or very cold places .
Also remember that the beta hCG level in your urine is often highest in the morning right after you wake up. Getting tested as soon as you get up can increase your chances of an early positive result.
And if the doubt remains?
In case of uncertainty, it is useless to disassemble the test, look at it against the light or photograph the negative: the test must be repeated after a few days.
In fact, we know that, if a woman is pregnant, beta levels double approximately every 2-3 days. Consequently, if the test is repeated after three days and the pregnancy is ongoing, that difficult-to-interpret clear stripe will become an obvious second line.
Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.
Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.