Nature's Repetitive Renewal
Many women think "menstrual cycle" refers only to the time of the month during which they experience their period. In fact, "menstrual cycle" is the entire reproductive system's month-long, cyclical process for preparing for and then disposing of the necessary matter to help a fertilised egg grow to full term.
Women typically experience their first period around age thirteen, and their last around age fifty-one. Every woman's cycles have different timing, although they all consist of the same basic parts, and cycles may be affected by illness, emotional state, changes in lifestyle or nutrition, or environmental factors.
Missing The Flow
Some women assume a late or missed period is an indication of pregnancy. Pregnancy tests can help determine whether or not you're pregnant, but they are not always accurate. The box may say "99% accurate", but that's based on many variables on either side. If the pregnancy tests have expired or been exposed to chemicals or moisture before use, they may not work properly anymore. Pregnancy tests that have been left in extreme temperatures, opened, or crushed are doubtful as well.
Depending on the time of day they're used, how long they were open before use, and your personal hygiene, the results of your pregnancy tests may not reflect the truth. Outside of all these factors, it's entirely possible for pregnancy tests to simply malfunction; they are an inexpensive home alternative to visiting the doctor or the health department. If you sincerely think you might be pregnant, you're better off getting a test from your doctor than spending money on home pregnancy tests.
It's also a good idea to remember that most women don't have their period like clockwork. A few days of delay aren't automatically an indicator that you need to start stocking up on pregnancy tests; they may be related to the amount of sleep you're getting, how well-hydrated you are, how physically active you've been recently, or whether you were recently ill. Even your stress level and mood can affect the way your body works.
All that being said, it is entirely possible to have a functional period during the first few months of pregnancy. While pregnancy tests shouldn't be your go-to solution every month, familiarize yourself with additional symptoms of first trimester pregnancy, and visit your doctor for more accurate and professional pregnancy tests than those offered by your local drugstore.
False Positives
Pregnancy tests work by measuring human Chorionic Gonadotropin, a hormone produced by the developing embryo and in later growth stages by the placenta. This means that only a pregnant woman can produce this hormone, which, in turn, means that positive results on pregnancy tests can only be achieved by a pregnant woman, logically speaking. This is assuming the pregnancy tests are not flawed or damaged in any way, and that the test is done exactly according to manufacturer's instructions.
However, those assumptions are not likely to be true. Many people who take pregnancy tests do not follow manufacturer's instructions; most of them ignore the instructions entirely, since pregnancy tests seem to be such a straightforward device. Some people take pregnancy tests the day after intercourse and expect them to have accurate results.
The best and, indeed, only time pregnancy tests are necessary, if ever, is within a week after the expected start date of a late or missing period. Taking pregnancy tests the morning after, or while menstruating, is more or less futile.
If you have very irregular cycles (as in, having your period more than once in a month, or going without one for two months or more without being pregnant), or find yourself frequently missing or skipping periods, talk to your doctor, as these may be signs of significant medical issues.
