Why Did I Have a One Day Period?

The “one day period” issue is something that can strike either fear or a spark of exciting hope within in a woman. It typically is associated with the question of “Am I pregnant?” When it comes to having a one day period, there could be a few different causes. For some women, this is an occurrence that happens once in a great while and for others it may be a one-off, never-before-experienced incident. Regardless of which group you fall into, you’re probably wondering what’s up with your body to cause such a shortened period. While nothing is certain, it can help to know the possible causes of this phenomenon so that you know where to start if any further action is necessary. Read on to learn a bit more about what may cause a single-day period.

Pregnancy/Implantation Bleeding

Yep, pregnancy is definitely a known cause for the one day period—and it’s probably the first cause to jump in your mind. Whether this idea excites or terrifies you—or perhaps a little of both—it may be a real possibility. To become pregnant, you have to have sex sometime around ovulation. Ovulation, the time when the egg is released from the ovary, usually occurs on the 14th day before your next period is expected. As semen can live inside your womb for up to a week, having unprotected sex even a week before ovulation can still see you with a good chance of conceiving.

You might be wondering what causes the one day period if you are pregnant. When the fertilized egg makes its way into the womb, it attaches itself to the lining of the uterus. This is called the process of implantation, and sometimes it can cause a bit of bleeding to occur. This can be in the form of a few heavy spots of blood or a flow of blood similar to a light day on your period. Implantation can also cause cramping and mild discomfort in the lower abdomen—similar to menstrual cramps. The early signs of pregnancy can also cause breast tenderness which you may be able to identify shortly after implantation.

The best way to figure out if you may be dealing with pregnancy and implantation bleeding is to calculate the date that you would have ovulated this past month and to try to remember if you had sex around this time. Once the egg is released you only have one day to fertilize is, unless the sperm is already there. Of course, it may be difficult to calculate the exact date, as ovulation can sometimes occur early or late. Therefore when making your calculations, you might want to allow a few days before and after your estimated ovulation date; and if you did have intercourse during this window of time, then you may be pregnant.

A pregnancy test probably won’t be able to detect your pregnancy until about 10 days after implantation bleeding occurs. Try to hold out this long before taking the test to lessen the chances of false results.

Hormonal Fluctuations

Hormones have a lot to do with when your period occurs, the duration of your period, and even the heaviness of your flow. If you’ve recently experienced a change in your hormones, such as taking a new birth control pill or experiencing unusual amounts of stress, then your one day period could be the result of a fluctuation of hormone levels. The main hormones responsible for causing your period are progesterone and estrogen. If these levels fluctuate too drastically it could result in a shortened period or even a missed period altogether. If you experience a single day period without any serious issues such as the passing of large blood clots or extreme pain in your abdomen, then you’re probably safe to move on without too much worry. If you start to develop signs of early pregnancy, such as breast tenderness, frequent urination, headaches, nausea/morning sickness, and eventually a missed period, then you may want to consider taking a home pregnancy test.


Have you recently battled with the flu, a cold, or a stomach bug? Sometimes a considerable illness, even a relatively short-term one, can affect processes in the body—the results of which are not immediately evident. One example would be the reproductive process. In times of sickness, your body’s immune system will become very preoccupied in destroying whatever pathogen has managed to creep into and take over your system. Believe it or not, it takes immense amounts of energy and resources for your body to fight an infection and as a result, other process may be put on hold so that the body can protect itself more efficiently. Think of it this way: your body, at the end of the day, has what you might interpret as a “choice” to reproduce. If your body’s health is at risk, it may actually choose health over the option to procreate. It’s kind of a built-in self-preservation instinct. So, if you have been sick recently, then there’s a good chance that your shortened period is the result of the illness.