The menstrual cycle is a symphony of hormones coordinated to yield an egg and to prepare the uterus and breast tissue for pregnancy. For most women, pregnancy will only take place in a very small percentage of cycles.

However, the monthly surge and fall of hormones starting in menarche and ending in menopause influences the brain, breast and uterus of women and may result in numerous symptoms throughout the month.

Menarche – The Beginning

The menstrual cycle will start with menarche around the average age of 12.5 years — down from approximately 17 years of age approximately 100 years ago. [1] Most young girls will start with very irregular cycles, progressing to regular cycles within 2-7 years, although anovulatory cycles are not uncommon especially when first cycling. [2] During early menarche, the coordination of the hypothalamus, pituitary and ovarian axis is maturing and the ovaries become fully developed. The negative and positive feedback loops are being established and the amplification of cyclical surges of hormones, particularly hypothalamus and pituitary hormones, is stimulated.

The menstrual cycle is divided into 4 main sections:

1. The menses – or “period”
2. The follicular phase
3. Ovulation
4. The luteal phase

Menses – "The Period"

During menses, the endometrial lining is shed (about 2 tablespoons). Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are expected to be in approximately a 1:1 ratio. Hormones are all at their lowest level of the month and the body tissues are given a rest from higher levels of hormones. During the period, the ovaries go through “follicular selection” when a small number of follicles approximately 5-10 mm in size become hormonally sensitive. The rest of the follicles regress or undergo atresia. 

Symptoms common during this time:

• Migraines and headaches
• Menstrual cramping
• Heavy bleeding / Lack of the menses
• Fatigue
• Pelvic pressure
• Mood disorders - depression

The Follicular Phase – Growing the Ovum and Endometrium

During this phase of the cycle, the rise of estrogen acts to stop menses. The endometrium is thickened, increasing from approximately 4 mm to 10 mm within 10 days. LH and estrogen cycle in a positive feedback loop that contributes to enlargement of the dominant follicle by 2-3 mm per day, growing it to approximately 18-25 mm in size at the time of ovulation. During this time there is a dramatic increase in estrogen and LH.  Symptoms during this time are usually minimal. But migraines and headaches are common with the rise of estrogen.

Symptoms common during this time:

• Migraines and headaches
• Persistent spotting or prolonged menstrual bleeding.
• Lack of endometrial growth
• Inadequate follicle growth

Ovulation – Releasing the Egg

During this phase of the cycle estrogen and LH peak, heralding the egg’s arrival. Within 10-12 hours of the LH peak (34-36 hours after the start of the surge), the egg is released from the dominant follicle. Ovulation often alternates between the left and right ovaries and some, but not all, women might notice ovulatory pain mid-cycle called Mittelschmerz, which is German for "middle pain." Women might also notice "ovulatory mucus" which tends to have the consistency of egg-whites – stretchy, watery, and abundant. 

Symptoms during this time include:

• Migraines and headaches
• Increased libido
• Ovarian pain
• Ovulatory spotting

The Luteal Phase – Enriching the Endometrium

The release of the egg (ovum) triggers the involution and development of the corpus luteum. The corpus luteum is essentially a hormonally active scar left on the ovary after the trauma of ovulation. It is the corpus luteum that will produce the progesterone and much of the estrogen in the second phase of the cycle. The ovum, after ovulation, moves through the fallopian tubes and is either fertilized or not. Meanwhile, the endometrium is changing reaching approximately 10-16 mm in thickness. The rise in progesterone stops the thickening of the lining and instead initiates the secretory phase. The dramatic rise in progesterone increases the blood flow to the uterus and endometrium. The endometrial glands in the uterine lining increase and start secreting glycogen, fructose and glucose into the endometrium to nourish any fertilized ova. The blood vessels within the endometrium become coiled. If pregnancy occurs, the rise in human chorionic gonadotropin (hCG) from the developing placenta will maintain the corpus luteum. But, in most cases, the corpus luteum will start to degenerate, the ovum dies and the lining of the uterus is completely shed. Estrogen and progesterone drop dramatically and the start of the next cycle begins. The luteal phase is very consistent in length from woman to woman and averages 14 days.

This is the stage of the menstrual cycle which generally produces the majority of problematic symptoms.

Symptoms common during this time — often just grouped as Pre-Menstrual Syndrome (PMS):

• Migraines and headaches
• Persistent spotting
• Mood disorders – irritability, premenstrual dysphoric disorder (PMDD)
• Acne
• Change in appetite – cravings, increased food intake
• Fibrocystic breast changes and breast pain
• Water retention
• Bloating
• Weight gain

Peri-Menopause – The Last Hurrah

Menopause is rarely the quick event of periods stopping and never having them again.  For most women, up to 10 years prior to menopause, ovulation stops being so dynamic, with less progesterone being produced from the corpus luteum and anovulatory cycles occurring more often.  The progesterone becomes relatively deficient compared to the peak reproductive years and women start noticing more symptoms of estrogen dominance.  In the cycle, the luteal phase may shorten showing less overall progesterone production and an earlier drop in progesterone.  This defines the condition commonly known as the luteal phase defect.  More PMS symptoms appear and arise earlier in the luteal phase.   Meanwhile, estrogen will slowly start to fluctuate more and more as the follicles fail to produce as much and the brain tries to compensate for the deficiency.  This will start to contribute to more symptoms, initially only at the times when estrogen already fluctuates and then eventually to the entire month.  It’s the fluctuations in estrogen that most likely contribute to vaginal atrophy and dryness, low libido, hot flashes, night sweats, memory changes, anxiety and insomnia.  LH levels start to rise as the brain tries to maintain consistent estrogen levels.  LH (and FSH) will become variable, but reach high levels years before menopause has truly arrived.

Menopause – The Conclusion of the Reproductive Chapter

Menopause is the absence of menstrual bleeding for a year in women over the age of 40 (Women who have no cycles under the age of 40 are generally dealing with other underlying health conditions, medications or autoimmune disorders). The ovarian egg reserves have been depleted. The ovaries stop responding to the now very high levels of LH. Progesterone levels have dropped dramatically and are basically non-existent.  Testosterone production continues from the ovaries, but the adrenal cortex will produce estrogen and progesterone for the rest of the woman’s life although at levels far lower than the ovaries did during the peak reproductive years.

The importance of a woman’s hormones from approximately age 12 until age 50 will for many women only cover approximately half of her lifetime. Yet, the consequences of hormone balance, or alternatively hormone imbalance, can influence every bodily tissue including the brain throughout the cycle and even after menopause.

Optimal hormone health requires a coordinated and elegant communication between the brain and ovaries that for many women does not occur. Testing the menstrual cycle throughout the month can allow women a peek into the times where symptoms are problematic. ZRT’s Menstrual Cycle Mapping profile gives you that peek into those levels.

Related Resources

• Blog: Feel Awful at "That Time of The Month"? It's More than Just Your Hormones. 
• Web: Menstrual Cycle Mapping
• Download: Menstrual Cycle Mapping Sample Report

References

[1] O’Grady 2008. Early puberty for girls. The new “normal” and why we need to be concerned. Canadian women’s health network. 11(1) 

[2] Zhang,K et al. 2008. Onset of ovulation after menarche in girls: a longitudinal study. J Clin Endocrinol Metab. 93(4): 1186-1194.