When you have a period, your body is shedding the nutrient-rich lining created during the previous cycle from inside your uterus. This occurs when estrogen and progesterone hormone levels decrease and there is no pregnancy.
Follicular phase (also known as the pre-ovulatory phase): This phase accounts for the first half of the menstrual cycle; beginning on the first day of your period and continues for 10 to 17 days. At birth, your ovaries contain all the immature eggs you will use during your entire lifespan. Under the control of various hormones following puberty, your brain will send a hormonal signal to the Follicle Stimulating Hormone (FSH) to your ovaries to recruit several follicles to mature each month. We can think of this as a race amongst the follicles as to which follicle will result in a mature egg to be released at the time of ovulation. Each follicle recruited during a cycle contains a single egg. The fastest, healthiest follicle and egg (also known as the dominate follicle) will win the race and release an egg (ovum) at the time of ovulation. The other follicles and eggs that were in the race are then reabsorbed, having lost their chance to fully mature or ever be released.
As follicles within the ovary race to mature, changes are also occurring within the lining of your uterus. Increasing amounts of estrogen stimulate a thickening of the lining of the uterus, known as the endometrium. This can be thought of as growing a thick, lush lawn, but instead of a lawn, you’re growing a nutrient-rich uterine lining in preparation to receive a fertilized egg. Estrogen is the fertilizer. The thickened endometrium or “bed of grass” is essential for a fertilized egg (egg + sperm = embryo) to attach or implant into the uterine lining. This is an essential process that occurs in preparation for an embryo (fertilized egg that will become a fetus) to attach or implant itself in the uterus and continue it’s development.
Other hormones are released near the end of the Follicular phase including testosterone. These hormonal changes are responsible for increased vaginal lubrication and an increase in libido or sexual desire. This is nature’s way of helping you to time sex to achieve pregnancy.
Ovulatory Phase: [Video explanation] Everything that took place during the Follicular phase has prepared your body for a spectacular series of hormonal events that lead to ovulation. Ovulation occurs mid-cycle in response to a series of hormonal changes that are set off by a peak in estrogen, occurring any day from day 10 to 17 of the Follicular phase. This peak in estrogen triggers a brief surge in Luteinizing Hormone (LH), which triggers ovulation within usually 24 hours and occasionally up to 48 hours.
Ovulation is the time when an egg is released from the dominant follicle (winner of the race) within an ovary, into the fallopian tube where it can become fertilized by sperm. This is the only time during the menstrual cycle that a woman can become pregnant. Women planning a pregnancy or using the “rhythm method” to prevent pregnancy often track their cycles using various methods such as body temperature, changes in vaginal secretions, and ovulation kits, also known at LH kits, to achieve pregnancy. If sperm are available, now is their chance! Once an egg is released, the egg is viable for up to 1 day, while sperm can be viable for up to 3 days. This means that the few days leading up to ovulation are the most fertile days of your cycle. With this is mind; conception is most likely to occur when sperm are available a few days prior to or just following ovulation.
Luteal Phase: [Video explanation]This part of the Ovulation Cycle lasts approximately 14 days. In this phase, the dominant hormone of the Follicular Phase estrogen declines and progesterone levels increase. Estrogen’s job was to fertilize and promote growth of the uterine lining and now progesterone’s job is to maintain that lining, or continue to “water the grass” so that a fertilized egg can implant or attach itself to the uterus. Progesterone levels are at their peak around 1 week after the LH surge, which coincides with the timing of embryo implantation, only if fertilization of the egg has occurred. The corpus luteum, which is what remains of the follicle in the ovary that released an egg at ovulation, is responsible for the increasing progesterone levels.
Human chorionic gonadotropin (HCG) is secreted by the embryo and becomes detectable in urine and blood samples approximately 2 weeks following implantation, or 4 to 5 weeks following the first day of your last period. Increased levels of progesterone also signal the ovaries to not produce any more eggs at this time.
If a fertilized egg has not attach itself to the uterine lining during the Luteal Phase, then progesterone levels will fall and the corpus luteum is reabsorbed a few days before your period starts. At the same time, the brain begins hormonal signaling all over again to prepare the next batch of follicles for the to race to ovulation! An Ovulatory Cycle, better known as your Menstrual Cycle, begins again! Menstrual cycles are normal anywhere from 24 to 35 days, with an average cycle of 28-30 days.
Cycles longer or shorter than this may or may not be ovulatory. Our Certified Nurse Midwives at the Alta View Nurse Midwives will be able to help you determine if this is the case, and how to promote ovulatory cycles.
Written by:
Alta View Nurse Midwives Jacqueline Lagana, CNM and Jennifer Jensen, CNM
801-501-3300