The Hormones of the Menstrual Cycle (and why they matter!)
In my last post, I outlined some reasons why understanding your cycle is super important! Today we’ll go a little more in-depth into the menstrual cycle and take a look at how it all fits together.
There are two main phases of the menstrual cycle: the follicular phase and the luteal phase. These two parts are separated by ovulation, which generally happens around the middle of the cycle, but can vary from woman to woman and cycle to cycle. In the first half of the cycle, our bodies are producing a lot of estrogen, and in the second half we are producing a lot of progesterone. Estrogen and progesterone have their own unique jobs in the body, and our fertility depends on them! The image below shows estrogen levels in blue and progesterone in red. The black line in the middle represents ovulation.
The bottom of the chart above shows what happens in the ovaries during each phase of the cycle: at the beginning of each new cycle, several immature eggs begin growing and developing. At some point during the follicular phase, one of the eggs emerges as the “dominant” egg, and continues growing alone (unless in the case of multiples, where two or more grow together). The egg grows because of the increasing levels of estrogen in the body. Eventually, the body reaches an “estrogen threshold” and the egg is developed enough to be released into the uterus. The egg breaks through the ovarian wall and ovulation occurs! It is swept up by the fimbria, small finger-like projections on the ends of the fallopian tubes) and is carried into the tube. If sperm are already present, fertilization can occur. If sperm are not present, the egg lives for only 12-24 hours and then is reabsorbed back into the body. The follicular phase has ended.
The other thing estrogen does is the production of cervical fluid! Cervical fluid is crucial for pregnancy, as it gives sperm a medium in which to swim once in the female body. Cervical fluid is produced by the cervical crypts, inside the cervix, and changes in consistency and color throughout the cycle. As a woman gets closer and closer to ovulation, the cervical fluid generally becomes more stretchy, wet and clear. Each woman has her own, unique cervical fluid pattern. Women who track this pattern each cycle can use the information to achieve pregnancy (they can time intercourse close to ovulation) as well as prevent pregnancy (they can identify when their fertility begins and ends, and avoid unprotected intercourse during that time). Cervical fluid is, unfortunately, often misunderstood (“What the heck is all this stuff on my underwear?!”) but is an amazing part of being a woman!
But back to the cycle: once the egg is gone, the casing of the egg that is left behind in the ovary turns into the corpus luteum. This tiny little temporary endocrine gland produces the hormone progesterone, which keeps the uterine lining intact for 10-16 days. Progesterone, just like estrogen, is also super important for pregnancy to occur, since it takes a fertilized egg about 7 days to travel and implant into the uterine wall. If progesterone doesn’t keep the uterine lining together, the fertilized egg has nowhere to implant and is swept from the body during the next menstrual flow. Progesterone also raises our body temperature, just slightly, which is how some women track if they’ve already ovulated or not.
The corpus luteum lives for about 10-16 days, waiting for another hormonal message (human chorionic gonadotrophin or hCG, the hormone that is tested for in pregnancy tests). If pregnancy has occurred, the corpus luteum will live for up to three months, continuing the production of progesterone until the placenta takes over. This progesterone production ensures the uterine lining is not shed. If pregnancy did not occur, the corpus luteum begins disintegrating, progesterone production stops, the uterine lining is shed and a new cycle begins. The whole thing starts over!
Understanding your hormones is not only a huge step in understanding your fertility and your reproductive health, but it’s also empowering to know how your body works. Check back for my next post on more information about how you can track your hormones and use the information they give to prevent or achieve pregnancy naturally. Until next time!
Latest posts by Ashley Annis (see all)
- The Hormones of the Menstrual Cycle (and why they matter!) - October 10, 2014
- 4 Big Reasons Why Understanding Your Menstrual Cycle Is Important - September 12, 2014