Estrogen

• Mid-cycle bleeding may occur right before you ovulate, or in the middle of your menstrual cycle, due to the decline in estrogen levels that occur before ovulation, according to Womenshealthcareforum.com. Ovulatory break-through bleeding is generally light and the blood may be brownish, according to Wdxcyber.com.
  
  

Young Girls, Older Women

• Mid-cycle bleeding is an instance of abnormal bleeding (bleeding when you shouldn't be). It happens to women who are peri-menopausal and menopausal as well as to young girls during the first two years following the onset of their menstrual period.
  
  

The Thyroid Connection

• If your thyroid is not functioning properly and you are suffering from either hypothyroidism (slow) or hyperthyroidism (fast) this can spell trouble for your menstrual period. You may have mid-cycle break-through bleeding or menorrhagia, which is excessive bleeding, or amenorrhea, which is the absence of your period. Your cycle may shorten from 30 days to, for example, 25 days. There is definitely a connection between thyroid function and your menstrual cycle, according to Thyroid-info.com.
  
  

Oral Contraceptives

• If you are taking oral contraceptives and miss a pill, this can cause mid-cycle bleeding, according to Yourtotalhealth.ivillage.com.
  
  

Intermenstrual Bleeding: The Official Name

• The medical term for mid-cycle bleeding is intermenstrual bleeding, according to Dr. Nirupama K. De Silva and Dr. Robert K. Zurawin. This bleeding can come from the vagina, perineum or the cervix. Targetwoman.com explains that mid-cycle bleeding is normal for some women and may occur just after they have finished up their period or earlier than expected in their regular cycle. Conditions and events that may exacerbate mid-cycle bleeding include hormonal changes and fluctuations, a miscarriage, the use of an IUD (intrauterine device), hypothyroidism, starting or stopping oral contraceptives, starting or stopping estrogen supplements, vaginal infection or injury, cervical cauterization or cone biopsy, and stress.
  
  

Other Conditions That Can Cause This

• Sometimes a woman experiences spotting mid-cycle rather than actual bleeding. Targetwoman.com notes that spotting can be caused by the mid-cycle shedding of the uterine lining during ovulation, certain medications, the egg bursting through the follicles in the uterus (which can cause bleeding that will manifest itself as spotting), cervical infections, cancer, birth control pills, polyps, fibroids, and the use of an IUD.