What are the stages of the female menstrual cycle and the associated hormone fluctuations?

From the Guidelines

The female menstrual cycle is characterized by a relatively predictable rhythm of 23-38 days, with fluctuations of hormones such as follicle-stimulating hormone, oestrogen, progesterone, and luteinising hormone, which separate the cycle into two major phases: the follicular phase and the luteal phase. The menstrual cycle can be broken down into the following stages:

• Menstruation: the uterine lining sheds due to low estrogen and progesterone levels
• Follicular phase: follicle-stimulating hormone (FSH) rises, stimulating follicle development in the ovaries, while estrogen gradually increases, causing the uterine lining to thicken
• Ovulation: luteinizing hormone (LH) surges dramatically in response to peak estrogen levels, triggering the release of an egg from the dominant follicle
• Luteal phase: the ruptured follicle forms the corpus luteum, producing progesterone and estrogen to maintain the thickened uterine lining for potential implantation These stages are associated with distinct hormone fluctuations, with estrogen and progesterone levels increasing during the luteal phase, and then declining before the start of a new cycle 1. The effects of these hormone fluctuations on energy metabolism and substrate preferences are significant, with high oestrogen levels during the luteal phase improving glucose metabolism by increasing glucose availability and glycogen storage in skeletal muscle and increasing the availability of free fatty acids and oxidative energy metabolism 1. Understanding these phases and associated hormone fluctuations is essential for women to track fertility, anticipate symptoms, and identify potential hormonal imbalances that might require medical attention.

From the Research

Stages of the Female Menstrual Cycle

The female menstrual cycle is characterized by several stages, including:

• Menstruation: initiated by progesterone withdrawal, resulting in shedding of the endometrium 2
• Follicular phase: FSH rise at the luteal-follicular transition, stimulating follicular growth and inhibin B secretion 3
• Ovulation: triggered by an LH surge, resulting from positive feedback of estradiol on the hypothalamus 4
• Luteal phase: corpus luteum secretes progesterone, oestradiol, and inhibin A in response to LH pulses, preparing the endometrium for implantation 3, 4

Hormone Fluctuations

Hormone fluctuations play a crucial role in the menstrual cycle, with:

• Estrogen (oestradiol) levels increasing during the follicular phase, stimulating endometrial proliferation 4, 5
• Progesterone levels increasing during the luteal phase, preparing the endometrium for implantation 3, 4
• FSH and LH levels fluctuating throughout the cycle, regulating follicular growth and ovulation 3, 4
• Inhibin B and inhibin A levels also fluctuating, playing a role in follicular growth and selection 3

Endometrial Changes

The endometrium undergoes significant changes throughout the menstrual cycle, including:

• Proliferation and differentiation in response to estrogen and progesterone 2, 4
• Preparation for implantation during the luteal phase, with peak progesterone production 4
• Shedding and repair during menstruation, triggered by progesterone withdrawal 2, 6