The fall in FSH allows smaller follicles to die off. They are, in effect, "starved" of FSH. When the level of estrogen is sufficiently high, it produces a sudden release of LH, usually around day thirteen of the cycle. This LH peak triggers a complex set of events within the follicles that result in the final maturation of the egg and follicular collapse with egg extrusion. Ovulation takes place 28 to 36 hours after the onset of the LH surge and 10 to 12 hours after LH reaches its peak.
The cells in the ovarian follicle that are left behind after ovulation undergo a transformation and become the corpus luteum. In addition to estrogen, they now produce high amounts of progesterone to prepare the lining of the uterus for implantation. The luteal phase, or second half of the menstrual cycle, begins with ovulation and lasts approximately 14 days — typically 12 to 15 days. During this period, changes occur that will support the fertilized egg, which is called an embryo, should pregnancy result.
The hormone responsible for these changes is progesterone, which is manufactured by the corpus luteum. Under the influence of progesterone, the uterus begins to create a highly vascularized bed for a fertilized egg. If a pregnancy occurs, the corpus luteum produces progesterone until about 10 weeks gestation. Otherwise, if no embryo implants, the circulating levels of hormone decline with the degeneration of the corpus luteum and the shedding of the lining of the uterus endometrium , leading to bleeding.
The lining of the uterus, or endometrium, prepares each month for the implantation of an embryo. This preparation occurs under the influence of estrogen and progesterone from the ovary. If no pregnancy develops, the endometrium is shed as a menstrual period, about fourteen days after ovulation. UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider.
We encourage you to discuss any questions or concerns you may have with your provider. Learn the steps of conception and how each works including, sperm transport, egg transport, fertilization and embryo development, and implantation.
Maternal age is probably the most significant factor related to a woman's ability to conceive. Menstrual cycles normally range from about 25 to 36 days. That is, they are longer or shorter than the normal range. Usually, the cycles vary the most and the intervals between periods are longest in the years immediately after menstruation starts menarche and before menopause. Menstrual bleeding lasts 3 to 7 days, averaging 5 days. A sanitary pad or tampon, depending on the type, can hold up to an ounce of blood.
Menstrual blood, unlike blood resulting from an injury, usually does not clot unless the bleeding is very heavy. The menstrual cycle is regulated by hormones. Luteinizing hormone and follicle-stimulating hormone, which are produced by the pituitary gland, promote ovulation and stimulate the ovaries to produce estrogen and progesterone.
Estrogen and progesterone stimulate the uterus and breasts to prepare for possible fertilization. The menstrual cycle is regulated by the complex interaction of hormones: luteinizing hormone, follicle-stimulating hormone, and the female sex hormones estrogen and progesterone. The menstrual cycle begins with menstrual bleeding menstruation , which marks the first day of the follicular phase. When the follicular phase begins, levels of estrogen and progesterone are low. As a result, the top layers of the thickened lining of the uterus endometrium break down and are shed, and menstrual bleeding occurs.
About this time, the follicle-stimulating hormone level increases slightly, stimulating the development of several follicles in the ovaries. Each follicle contains an egg. Later in this phase, as the follicle-stimulating hormone level decreases, only one follicle continues to develop.
This follicle produces estrogen. The ovulatory phase begins with a surge in luteinizing hormone and follicle-stimulating hormone levels. Luteinizing hormone stimulates egg release ovulation , which usually occurs 16 to 32 hours after the surge begins. The estrogen level decreases during the surge, and the progesterone level starts to increase. During the luteal phase, luteinizing hormone and follicle-stimulating hormone levels decrease.
The ruptured follicle closes after releasing the egg and forms a corpus luteum, which produces progesterone. During most of this phase, the estrogen level is high.
Progesterone and estrogen cause the lining of the uterus to thicken more, to prepare for possible fertilization. If the egg is not fertilized, the corpus luteum degenerates and no longer produces progesterone , the estrogen level decreases, the top layers of the lining break down and are shed, and menstrual bleeding occurs the start of a new menstrual cycle.
If the egg is fertilized, the corpus luteum continues to function during early pregnancy. It helps maintain the pregnancy. The follicular phase begins on the first day of menstrual bleeding day 1. But the main event in this phase is the development of follicles in the ovaries.
At the beginning of the follicular phase, the lining of the uterus endometrium is thick with fluids and nutrients designed to nourish an embryo. If no egg has been fertilized, estrogen and progesterone levels are low. As a result, the top layers of the endometrium are shed, and menstrual bleeding occurs. About this time, the pituitary gland slightly increases its production of follicle-stimulating hormone.
This hormone then stimulates the growth of 3 to 30 follicles. Later in the phase, as the level of this hormone decreases, only one of these follicles called the dominant follicle continues to grow. The follicular phase starts with the first day of your period and ends with ovulation. What happens during the follicular phase? Early phase At the beginning of your cycle, estrogen and progesterone levels are low.
Mid-phase Several follicles will grow to the antral stage which means there is a fluid-filled cavity in the follicle next to the egg. Late phase A dominant follicle emerges, which continues to produce rising levels of estradiol and inhibin A. This is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
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