The Menstrual Cycle
During the menstrual cycle, fluctuations in sex hormone levels prepare a woman’s reproductive system for pregnancy. A normal cycle generally ranges from 25–36 days. The first day of menstruation is considered day one of the cycle and is part of the follicular phase (Brzyski 2013). Key hormones involved in the menstrual cycle are luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen, and progesterone. The fluctuation pattern of these hormones over the course of the menstrual cycle is depicted in Figure 1.
- Follicular phase. The follicular phase, which begins on the first day of menstrual bleeding, usually lasts 13–14 days (Hawkins 2008; Brzyski 2013).
- Ovulatory phase. The ovulatory phase usually lasts for 16–32 hours and occurs at approximately day 14 of the menstrual cycle (Hawkins 2008; Brzyski 2013; Ajala 2013).
- Luteal phase. The luteal phase usually lasts for approximately 14 days (Hawkins 2008; Brzyski 2013).
- Menstruation. The entire menstrual cycle resets itself on the first day of menstruation, and the process is repeated (Hawkins 2008; Brzyski 2013).
In order for a woman to be diagnosed with PMS, troublesome symptoms must occur during the luteal phase of the menstrual cycle, end soon after menstruation, and not recur until the next luteal phase.