Articles by Dr. Lotte Valentin

The Menstrual Cycle


Women usually start menstruating during their pre-teen or early teen years, and many experience a variety of symptoms and discomforts associated with this monthly cycle. However, not many women are familiar with how to help themselves feel better.


In this article we’ll look at how the normal menstrual cycle works, and in upcoming newsletters we’ll explore some of the issues that can be associated with it and how to address them naturally.


The day count for menstrual cycle begins on the first day of menstruation, and the average length of the cycle for most women is about 28 days. The menstrual cycle can be divided into four main phases and on average the days are divided as follows.

1.    Menstrual phase (day 1 to 5)

2.    Follicular phase (day 1 to 13)

3.    Ovulation phase (day 14)

4.    Luteal phase (day 15 to 28)


Menstrual phase (day 1-5)

The menstrual phase begins on the first day of menstruation and lasts on average till the 5th day of the menstrual cycle. (This can vary, depending on the woman.)

·       The uterus sheds its inner lining of soft tissue and blood vessels which exits the body in the form of menstrual fluid.

·       Menstrual cramps are common and are caused by the contraction of the uterine and the abdominal muscles to expel the menstrual fluid.

Follicular phase (day 1-13)

This phase also begins on the first day of menstruation and lasts on average till the 13th day of the menstrual cycle. The follicular phase is what determines how many days there are in between your cycles. The amount of time it takes for the ovum to grow in the follicles varies from woman to woman, which can vary the length of the follicular phase and cause the cycle length to be different for each woman. 

·       The pituitary gland secretes a hormone (FSH—follicle stimulating hormone) that stimulates the egg cells in the ovaries to grow.

·       One or more of these egg cells begins to mature in a sac-like-structure called a follicle. It takes on average 13 days for the egg cell to reach maturity, but can also vary between women. If 2 eggs mature and are released it may allow for the fertilization of twins.

·       While the egg cell matures, its follicle secretes a high amount of estrogen, which stimulates the maturation of the egg and eventually causes the release of the egg into the fallopian tube, as well as preparing the uterus to develop a lining of blood vessels and soft tissue called endometrium.


Ovulation phase (day 14)


·      Ovulation occurs on day 14 in a 28 day cycle, but if the cycle is 35 days the ovulation would take place on day 22. The ovulation day varies as the length of the follicular phase varies between women.

·      The increasing estrogen levels from the follicles creates a positive feedback loop to the pituitary gland and causes a spike in LH right before ovulation.

·      This then increases the secretion of estrogen from the ovaries, causing the ovary to release the matured egg cell (ovulation) as well as initiating the release of progesterone.  

·      The released egg cell is swept into the fallopian tube by the cilia of the fimbriae. Fimbriae are finger-like projections located at the end of the fallopian tube close to the ovaries and cilia are slender hair like projections on each fimbria.


Luteal phase (day 15-28)

This phase begins on average around the 15th day, which is 14 days before menstruation in a 28 day cycle, and lasts till the end of the cycle.

·       The egg cell released during the ovulation phase stays in the fallopian tube for 24 hours. If a sperm cell does not impregnate the egg cell within that time, the egg cell disintegrates.


·      The ruptured follicles form the corpus luteum increase the release of progesterone and estrogen. The increase in hormones takes place during the first four to five days of the luteal phase, which helps prepare the uterus for implantation. The progesterone helps thicken the walls of the uterus and makes them have a more spongy consistency.


·      The corpus luteum has a life span of about 12 days, and if there is no fertilization and implantation, it degenerates (luteolysis), and the production of progesterone and estradiol decline rapidly, causing the menstrual phase of the next cycle to begin. The endometrium is most conducive to implantation around the fifth day of the luteal phase.


The hormonal pattern of the menstrual cycle is regulated by the hypothalamus and pituitary glands in the brain. The hypothalamus, which is about the size of a pea, is situated between the thalamus and pituitary glands and links your nervous system to your endocrine system.


The hypothalamus sends signals to your pituitary via a hormone called Gondadotropin Releasing Hormone (GnRH), which signals the pituitary to release FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone). LH and FSH then send signals to your ovaries and adrenal glands to make Estrogen, Progesterone and Testosterone.


There are three different kinds of estrogens: estrone (E1), estradiol (E2), and estriol (E3). Estradiol (E2) is the strongest of the estrogens and is 12 times stronger than estrone (E1) and 80 times stronger than estriol (E3). In a non-pregnant woman, most of the estrogens are produced in the ovaries and adrenal cortex. Beta-estradiol is produced in the ovaries and estrone is produced in the adrenal cortex and ovaries from Beta-estradiol and androstenedione. Estriol is formed in the liver by conversion of either beta-estradiol or estrone. Progesterone and testosterone are also produced in the ovaries and adrenal cortex.


The fluctuating levels of estradiol, progesterone and testosterone affect many things, including a woman’s menstrual cycle, mood, sleep patterns, PMS, appetite and sex drive. See Menstruation, PMS and PCOS article for more information on this topic.

The information contained on this site is for educational purposes only.  These statements have not been evaluated by the Food and Drug Administration and are not intended to diagnose, treat, cure, or prevent any disease. Please discuss all your medical issues with your doctor.