Can I trust my home pregnancy test?
If you think you might be pregnant, chances are you will use a home pregnancy test to see if your hunch is right. All pregnancy tests, whether a home kit or one you take at the doctor’s office, measure the amount of a hormone, called human chorionic gonadotropin (hCG), released in early pregnancy and sometimes called the pregnancy hormone.
Here’s how the kits work: When an egg is fertilized by a sperm in the fallopian tube, the resulting embryo travels down the fallopian tube to the uterus, where it implants. The embryo releases the human chorionic gonadotropin (hCG) pregnancy hormone. This hormone is what gives the embryo the signal to “stick” to the uterus, and the embryo implants into the uterus around six days after fertilization.
The pregnancy hormone hCG is released as early as four to five days after fertilization, and its level increases exponentially, doubling each day during the first few days, reaching a peak at around eight to nine weeks. The level of hCG is what is measured by your home pregnancy test kit.
Home pregnancy tests work by measuring the level of the hCG pregnancy hormone in your urine. The classic “pee on a stick” involves dipping a test kit strip into urine collected preferably early in the morning (since the level of hCG is highest then), or by urinating on the strip of paper.
The paper strip can then be inserted into a reader, which then gives two read-outs:
After the required amount of time for the reaction to take place – this may vary from 2 to 90 minutes – but it’s usually on the shorter side -- the result appears on the result screen on the reader.
The principle behind the test is this: hCG binds to a specific antibody, i.e. a protein which binds only hCG. This antibody is linked to a color indicator, which colors a certain line to show a positive test. If the control indicator does not appear, the test is not working properly. You should not rely on any results from a test that may not be working properly.
You should know also that home pregnancy tests vary widely in sensitivity levels. Some tests detect very low levels of hCG and can tell if you are pregnant about five to six days before your missed period. Most brands tell you to repeat the test in a week’s time if the test is negative, just to be sure that you’re actually pregnant, but did the first test too early. If tested according to the manufacturer’s instructions, most home pregnancy tests are about 97% accurate. How accurate a home pregnancy test is depends upon how closely you follow instructions, how soon you take the test, and the sensitivity of the test assay.
False positives (meaning, the test tells you you’re pregnant when you’re not) are uncommon, but they do happen under certain conditions: For example, if you have taken a fertility drug containing hCG (used to induce ovulation in fertility treatments) or you have had a miscarriage or a pregnancy termination in the last eight weeks.
If you are not certain about the accuracy of your test, we encourage you to consult with your doctor. Your doctor may order a blood test, which can detect very low levels of hCG, making it possible to detect pregnancy several days before your period is expected to start.