Evaporation Lines and Early Pregnancy Tests Home pregnancy tests: When an ovum is fertilized in your body and after the embryo attaches to the uterine wall the newly formed placenta produces the pregnancy hormone or Human Chorionic Gonadotropin (hCG). Home pregnancy tests contain monoclonal antibodies, which are molecules coated with a substance that bonds to Human Chorionic Gonadotropin (hCG). If Human Chorionic Gonadotropin (hCG) is detected, the test reacts with a positive sign. There are different types of home pregnancy tests and you can use them at home or in a clinic. Most doctors recommend that you wait until the first day of your missed period before taking a home pregnancy test. This is usually about two weeks after conception. However, some tests are more sensitive than others and can be taken earlier. The first type of home pregnancy tests - dip tests, involves collecting your urine in a cup and dipping a stick into the urine, or putting urine into a special container with an eyedropper. A second type of home pregnancy tests-stream tests, involves placing a stick into your urine stream and catching your urine in midstream. Tests vary in how long you have to wait to get a result. This time period is called reaction time of the test. You will be looking for a change in color, a line or symbol (like a plus or minus). All tests come with instructions and it is important that you follow these instructions to get an accurate reading. What are evaporation lines? Evaporation lines, as the name suggests are caused due to evaporation of the urine in then test area. These are lines that shows in the result window of the test, exactly where a positive sign would be. An evaporation line develops when the urine on the test area begins to dry, leaving a faint, usually colorless line. Evaporation lines appear to show up (or not show up) as a result of the composition of the particular urine specimen - and they may appear on any test regardless of brand. How can you avoid formation of evaporation lines? You should always read the literature that comes with the test and look for instructions on when to read your results. Usually home pregnancy tests have a reaction time of three to five minutes. While some tests are no longer accurate after a certain amount of time, others have been known to pick up Human Chorionic Gonadotropin (hCG) after a longer period of time than is recommended. You can only know for sure by testing again a few days or a week later. If you don't see a positive result in the amount of time that the manufacturer states, you should not rely on that test result. Evaporation lines can cause confusion if the home pregnancy test is not interpreted within the clinically recommended time frame.