The menstrual cycle is the monthly reproductive lifespan experienced by females that involves the fluctuation of numerous hormones that stimulate a variety of responses and changes within the body, all for one common goal…ovulation. Although no two cycles are the same, most women experience a cycle lasting about 28 days, but can vary between 21-35 days. As a woman, it is important to have an idea of how many days your cycle is, and what is typical for you. Not only can this help to identify any deviations from the norm, but the length of the cycle is a crucial factor in determining the different phases of ovulation. Although every woman has a different cycle, ovulation (release of the female reproductive egg) is invariably always 14 days before the onset of menstruation (the first day of your period). This can be important when trying prevent or get pregnant. If it is assumed that ovulation occurs in the middle of a 35 day cycle, timing sexual intercourse can be off, resulting in less than desired outcomes, such as unplanned pregnancy, or during times of infertility.
Now for the technical stuff….the menstrual cycle is initiated by the release of a chemical called Gonadotropin Releasing Hormone (GnRH) by the hypothalamus (the control center of the brain). This hormone is usually secreted in pulses, about every 90 minutes, and fluctuating throughout the cycle. Increases in GnRH act on the pituitary gland in the brain in response to low circulating estrogen levels in the body, and stimulates the secretion of two more very important hormones, Lutenizing Hormone (LH) and Follicle Stimulating Hormone (FSH). FSH acts on the ovaries to promote follicle stimulation (hence the name), in order to basically “grow” a new egg each month. With the rise in FSH, the ovaries begin to secrete estrogen, which increases the circulating levels, and at first, in order to regulate production, signals to the pituitary gland to decrease the amount of hormones being produced, with a system known as the negative feedback mechanism. When estrogen levels increase to reach a certain point, however, this mechanism in the brain is reversed, and LH is rapidly secreted in what is called an LH surge. When this surge occurs, the follicle sac with the egg ruptures, releasing the egg (ovulation), and can be expected to occur in approximately 10-12 hours. Soon after release, the ruptured follicle becomes enlarged and firm (which is why it is not uncommon to experience tender, physiologic ovarian cysts during ovulation) and it becomes the corpus luteum (CL). This transition is a key contributor to the final phase of the cycle, so called the Luteal Phase. The CL secretes progesterone and estrogen to restart the negative feedback loop on the hypothalamus, and prevent further ovulation. ***Rises in progesterone levels promote the production of endometrial (uterine) lining in preparation for potential egg fertilization and implantation. This lasts from about Day 15-Day 28, and is important because this will not occur if there is no ovulation***.Within a couple days, the CL begins to degrade, decreasing progesterone and estrogen levels, which degrades the inner uterine lining, causing disruption of the uterine vessels and subsequent bleeding into the uterine cavity. The tissue disruption stimulates the inflammatory response in the uterus, by which chemicals are secreted that cause the notorious symptoms of menstruation: swelling (bloating), contractions of the uterine muscles (cramping), and sloughing of the degraded endometrial tissue (bleeding), thus indicating the start of a new cycle.
How do hormonal contraceptives and birth control pills play a role in this? Well, contrary to popular belief, taking the pill does not “fool” your body into thinking it is pregnant. Come on, you think its THAT simple?! Actually, most contraceptives work by providing a steady dose of estrogen (amongst other things), that keeps the LH levels low, preventing the monthly release of an egg. Similarly, many forms of the pill provide steady, low doses of progesterone, which limits endometrial proliferation, and often contributes to the lighter periods women experience when they are on the pill. When the steady doses of these hormones are stopped, such as at the end of the pack of pills, or when a pill is missed, the rapid decline in estrogen and progesterone stimulate the endometrial degradation and bleeding that occurs. Furthermore, the decline in estrogen levels may cause an LH surge. If this occurs midcycle, release of an egg may occur. If unprotected sex occurs at this time….oopsies.
So now you may be asking, “well if all this is occurring internally, how do I KNOW when I am at risk for being fertile?!” The answer….? Know yourself, be in tune with your body. OK so that sounds super tree-hugger I know, but it really is that simple. For one, just knowing how often and when to expect your period each month can provide you plenty of information on what is going to happen, and when (remember ovulation always occurs 14 days BEFORE you get your period!). Additionally, being aware of changes in your body helps too. First of all, estrogen plays a huge role in the female sex drive. When estrogen spikes just before ovulation, many women feel very sexually stimulated (naturally a response to the innate reproductive instinct). Any sudden sexual desires midway between periods might give you a clue as to what ovulatory phase you are in. You may have heard of checking your basal body temperature when trying to get pregnant. This is very accurate, HOWEVER, the increase in temp is VERY slight, so temperature must be by a precise thermometer, by the same route (if taken orally it must be done orally every day) at the same time every day, and must be recorded. It can be a tedious task, and will take some practice. Finally, there is one of the easiest ways, which is where I encourage the “know your body” saying. Just like the cells that make up mucus secreting cells in the gastrointestinal tract, mouth/nose, and respiratory tract, and any opening to your body, the female genitalia are also composed of similar cells that secrete mucus (preventing infections), particularly, in the cervix. At the beginning of the month, during the infertile phase, the cervical mucous is often thick, dry and sticky. Remember that the cervix is the opening into uterus, the only route accessible to sperm for fertilization. When the cervix secretes this thick mucous, its matrix like properties form a plug that prevent sperm from entering the uterus. During this time, little to no mucous can be identified in the vagina. As ovulation approaches, the cervix becomes soft and vascular, and it begins producing increased amounts of mucous. These secretions, however, are not only copious in amount, but they have the consistency of egg whites (or snot), and are often clear, thin, and stretchy (known as Spinnbarkeit) and it has vertical microscopic properties that allow sperm to enter the uterus in search of an egg. When ovulation is over and progesterone levels increase, the cervical mucous returns to being “thick and hostile” once again. In order to determine which stage your cervical mucous is in, you may need to…explore your true self a little. Today’s society doesn’t always encourage this method, but screw it. Nature knows whats up, so should you.
After all that, my final words of advice for today are as follows…
1. Know your own unique cycle. Know whats normal for you, and be smart about.
2. Don’t miss your pills. If you do, use protection.
3. Understand that the cycles ALWAYS start on the FIRST day of your period. People often seem confused when asked the date of their last period, and give the last day. This messes up everyone’s calculations.
4. Don’t be afraid of know and be comfortable with yourself and the changes your body is constantly going through, whether it be on the course of puberty to menopause, or the monthly changes of the menstrual cycle.
5. Love your nurse-midwife.