A one-day period can result from hormonal fluctuations, the use of certain contraceptives or excessive stress on the body, says MedGuidance.com. A one-day period with very light bleeding can also indicate pregnancy, as implantation bleeding typically takes place around the same time a missed period is expected to appear. Caused by a fertilized egg attaching to the uterine wall, implantation bleeding typically consists of light spotting, with or without cramping.
Estrogen is the regulator of the menstrual cycle, and any change in estrogen levels can cause a woman's period to change, according to MedGuidance.com. While estrogen levels are increasing in young women, they are decreasing in perimenopausal women, and these changes can make for a short period every once in awhile. Oral contraceptives, injected contraceptives and intrauterine devices all cause fluctuations in estrogen levels that can lead to a short, one-day period. Changes in diet or exercise and excessive mental or physical stress can all cause fluctuations in estrogen levels that then cause the period to be shortened.
If any other signs of pregnancy occur, such as morning sickness, fatigue, food aversions, breast tenderness or the need to urinate frequently, MedGuidance.com advises taking a pregnancy test. If results are negative and irregular cycles continue to occur, the woman should schedule a doctor's appointment to discuss possible reasons for the problem.