The Menstrual Cycle

In order for a woman to have the potential to become pregnant the following must be true of her menstrual cycle so that fertilization and implantation is possible. The woman’s ovarian and anterior pituitary hormones behave normally during her cycle to develop a mature egg and prepare the uterus for implantation.

The below chart illustrates the changes in a woman’s body during the menstrual cycle. Each term is explained in the following glossary.

The Menstrual Cycle


Ovarian Cycle

Follicle Development

  • Primordial Follicle: A resting follicle that holds an immature egg.
  • Primary Follicle: A follicle that has grown to .1mm in diameter.
  • Secondary Follicle: A follicle that has developed a fully grown egg and is .2mm in diameter (note: not all follicles contain an egg).
  • Preantral Follicle: A follicle that is approximately .2-5mm in diameter.
  • Antral Follicle: A follicle that is approximately 10-20mm in diameter.

Ovulation: When the ovaries release a mature egg that is ready for fertilization.

Corpus Luteum: Forms from the ruptured follicle after ovulation and helps prepare the uterus for implantation.

Corpus Albicans: Forms from the breakdown of the corpus luteum when fertilization of the egg does not occur.

Basal Body Temperature (BBT): The body temperature at rest taken in the morning before arising from bed that can be used to help identify the time or presence of ovulation.

Anterior Pituitary Hormones

Follicle Stimulating Hormone (FSH): A hormone released from the brain that causes follicles in the ovaries to grow.

Luteinizing Hormone: A hormone released from the brain that triggers ovulation.

Ovarian Hormones

Estrogen (Estradiol, E2): A hormone produced primarily in a woman’s ovaries that helps regulate ovulation and uterine lining development.

Progesterone: A hormone that is produced by a woman’s ovaries or a medication that prepares the uterine lining for implantation.

Uterine Cycle

Menses: The discharge of blood and other tissue after ovulation when fertilization does not occur.

Follicular Phase: The first phase of the menstrual cycle, from onset of menses to ovulation, in which ovarian follicular growth occurs, in response to hormones. This phase is variable in length in women, but on average lasts approximately 14 days.

Luteal Phase: The second phase of the menstrual cycle beginning from ovulation until the onset of menses. It is associated with hormones that facilitates implantation of the embryo(s) and supports early pregnancy. This phase is typically 12-14 days in all patients.