Let’s understand all about evaporation lines and sort out your doubts.

Introduction: Decoding Evaporation Lines on Pregnancy Tests

An evaporation line is a streak that appears where the positive line on a pregnancy test should be. It is not a faint line: it is just a colourless streak. These streaks appear when the test is left aside too long. They do not indicate pregnancy.

How Pregnancy Tests Work: Mechanism and Accuracy Explained

Once a fertilised egg has implanted, a hormone called hCG is released in the woman’s body. It grows rapidly in the first trimester and its traces are easily detectable in the urine.HCG increases quickly (almost doubling every three days) for the first eight to 10 weeks of pregnancy. Some women can have traces even before the missed period, some may take longer. The pregnancy test stick has compounds that react to those traces and form lines (some have dots or alphabets) to confirm pregnancy.

• The average hCG concentration in urine at 9 days after ovulation — around 5 days before a missed period — is 0.93 milli-international units per millilitre (mIU/ml). 

• Most early-result pregnancy tests can only detect hCG when it rises to levels of 25 mIU/ml or higher.

• By day 14, hCG levels are typically around 137 mIU/ml. For some people, however, they can be as low as 45 mIU/ml.

False negatives are more common than false positives. If the result is negative, it may be a good idea to take another test in a few days, to give the hCG levels a chance to rise.

There are, however, some unusual circumstances that can cause a test to come out positive in the absence of pregnancy. Examples include familial hCG syndrome, molar pregnancy, or conditions that affect the pituitary gland.

Home pregnancy tests are 99% accurate. Make sure you have not stored them in a very warm (above 38 degrees Celsius)  or very cold place (below 2 degrees Celsius) and they are not past their expiration date. Here are some other things to consider:

1. Take the test with the first urine of the morning.
2. Don’t drink lots of fluids before you take a pregnancy test. This can dilute your HCG levels.
3. Pee in a cup, then dip the test in the urine for the duration specified on the box. Directly peeing on the stick can cause too much splashing on it.

If not convinced with a negative result, please give hCG levels time to rise and take another test in a few days. This can reduce the risk of false negatives.

What is an Evaporation Line on a Pregnancy Test? 

Each woman’s chemical composition may be different and could cause such lines to appear. These are colourless lines where the actual line has to appear. Actual lines will have a colour - most brands have pink, red or blue.

One of the best ways to avoid any confusion when using a home pregnancy test is to check your results within the reaction time. Please follow the instructions written on the pack.

Some pregnancy tests have instructions to check results after two minutes. Others have instructions to check results after five minutes. The risk of a false positive is higher when you read your results after the reaction time specified in the instructions.

Do evaporation lines get darker the longer it sits? No, that doesn’t happen. If your line is getting darker, it's more likely to be either the control line (this is generally the darkest line on a pregnancy test) or a positive result. Evaporation lines on pregnancy tests usually get lighter as your pee evaporates.

The Difference Between a Faint Positive Pregnancy Test and an Evaporation Line

The most significant differentiator is the colour. An evaporation line will not have any colour. It will be greyish and look like a streak not really a line. A faint positive is likely to have a very light colour. So, try taking it again in a few days.

A faint positive could mean that the levels of hCG hormone, often referred to as the pregnancy hormone are low. So, if you see a faint line on your home pregnancy test, this simply means that the hCG hormone level in your urine is low, and you want to try again in the morning when it's more concentrated or levels have risen.

Next steps after Home Pregnancy Test

While these tests are usually effective, there are chances of a false negative or a false positive. A false negative mostly occurs if you take a pregnancy test too early, including before a missed period when your hCG levels aren’t high enough.

False positives are less common, one reason for those is a chemical pregnancy. Molar or ectopic pregnancy is when the fertilised egg implants outside the uterus and a miscarriage occurs shortly after.

If you think you’re pregnant, or if you’re confused by the results of a home pregnancy test, it's best to see a doctor immediately.

Even if the home test is positive, it is advised to see a doctor to check if the baby has implanted correctly in the womb and get advice on your prenatal vitamins.