Hormone Cycle Basics Everyone With A Uterus Should Know

Education for young people with a uterus and ovaries about their monthly hormone cycles is sadly lacking.

For many, the only education they received came from a basic sex ed class in high school, and I haven’t heard of anyone walking away knowing how to identify the signs of ovulation or how to determine their fertile window, for example. Most of us received “abstinence only” education, which by nature liberated our instructors from explaining the most useful concepts of fertility that empower women either to avoid pregnancy or to understand the best times to try for pregnancy.

If your cycle is a mystery to you, what follows is a peak behind the curtain that explores the various stages and their hormonal underpinnings. Take a look at the chart above to see an illustration of hormone fluctuations throughout the month and follicle development in the ovaries.

WHICH COMES FIRST?

Even though menses is the “first” phase in the cycle, I’m going to start with the follicular phase because menses follows ovulation, not the other way around. Although it’s possible to bleed without ovulating, true menstruation occurs as a direct result of the hormonal process of ovulation.

FOLLICULAR PHASE

The first thing to know is that the brain is responsible for initiating the hormonal cycle, and it does so when it senses that environmental conditions are appropriate for reproduction: for example, stress levels are low and the body is receiving adequate calories. When stress is quite high or caloric intake is too low, the brain may decide that it’s not a good time to have a baby. It can put on the brakes and delay ovulation or even temporarily stop signaling the ovaries to ovulate, which will, in turn, either delay menstruation or cause it to stop altogether.

When the body is in balance and one is experiencing healthy hormone cycles, the pituitary gland (in the brain) releases Follicle Stimulating Hormone (FSH) to stimulate egg follicles to grow in the ovaries. As the follicles grow, they secrete higher and higher levels of estrogen.* The strongest follicle secretes enough estrogen at some point that it signals to the other follicles that they are no longer needed and they shrivel up, leaving one dominant follicle (usually).

Meanwhile, increasing estrogen levels cause the endometrial lining to grow and thicken while also promoting the secretion of fertile cervical fluid. (It’s really called “cervical mucus,” but who wants to use that phrase?!) These changes are important for fertility: a nice thick endometrium is required for implantation of a fertilized embryo, and fertile cervical fluid is beneficial because it helps sperm survive and reach their destination.

*To be precise, the follicles secrete androgens, but the androgens get converted to estrogen if everything is working properly. This conversion does not work properly in PCOS, which is why ovulation is disrupted and why women end up with androgenic symptoms such as acne, male pattern hair loss, and facial hair.

OVULATION

As the dominant follicle approaches full maturity, it secretes more and more estrogen, which ultimately signals the brain that the follicle is ready for ovulation. In response, the pituitary gland releases a surge of Luteinizing Hormone (LH) which triggers ovulation. The LH surge is what is detected with an ovulation predictor kit (OPK). Thirty-six hours after the LH surge, ovulation occurs: the egg pops out of the follicle and is taken up into the fallopian tubes.

LUTEAL PHASE

After the egg pops out of the follicle, the follicle gets a new name: the corpus luteum. The job of the corpus luteum is to secrete progesterone, which matures the endometrial lining in preparation for implantation and also sustains an early pregnancy if fertilization and implantation has occurred.

Progesterone also increases basal body temperature, which is why basal body temperature (BBT) charting can be used to track ovulation. BBT charting is particularly useful for women who are trying to conceive and women who are using Fertility Awareness Method (FAM) to avoid pregnancy.

MENSTRUAL PHASE

If fertilization and implantation do not occur, the corpus luteum disintegrates and progesterone production falls away, which in turn destabilizes the uterine lining and causes it to slough off in the process we know as menstruation.

PREGNANCY

If fertilization and implantation occurs, the embryo secretes human chorionic gonadotropin (HCG) which will maintain the corpus luteum so that it continues to produce progesterone through the first trimester until the placenta is developed enough to take over hormone production. If you are tracking your BBT, a sign of pregnancy is consistently elevated temperatures for more than 16 days.

FERTILE WINDOW

Now that we’ve been through the phases, you might be wondering when you are most fertile in your cycle. Peak fertility occurs in the days leading up to ovulation and is accompanied by “eggwhite” cervical fluid that is clear and stretchy. It’s also when the cervix is at its highest position.

For couples who are trying to conceive, timed intercourse is usually recommended every other day for 5-6 days leading up to ovulation, because the sperm should ideally be ready and waiting at the end of the fallopian tubes by the time ovulation occurs. For couples using FAM to avoid pregnancy, the safe window starts after about 3 days of high post-ovulation temperatures and continues through at least the first few days of menstruation.

A QUICK NOTE ON THE PILL

FYI, the birth control pill stops this hormonal cycle in your body by preventing ovulation. There are a few things you should know:

• The monthly bleed you experience on the Pill isn’t a period but a withdrawal bleed from the withdrawal of the synthetic hormones on your sugar pill days.

• Because you don’t ovulate, you aren’t making your natural estrogen and progesterone, which means that you’re missing out on the benefits those hormones provide for mood, heart, and bone health.

• The Pill depletes essential minerals and vitamins from your body, so it’s important to supplement them to maintain thyroid function, mental health, and overall well-being. I also recommend discontinuing the Pill six months to one year before trying to conceive to get your natural cycle back on track, to replenish nutrients, and get your body prepared for pregnancy.