Living Glossary
Welcome to the Living Glossary, a growing collection of reproductive health terms explained in plain language.
As new topics are explored through Menstruation to Menopause, new terms will be added to the glossary. Existing definitions will be reviewed periodically to help ensure they continue to reflect current medical guidance.
The Living Glossary draws from trusted medical resources, including the American College of Obstetricians and Gynecologists (ACOG), the Office on Women's Health (OWH), and MedlinePlus.
Browse the glossary by selecting a letter below.
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C
Cervical Mucus
A fluid produced by the cervix that changes in amount and texture throughout the menstrual cycle. Around ovulation, cervical mucus usually becomes thinner and more slippery, which can help sperm move through the cervix. It also helps protect the reproductive system from bacteria and other germs.
Cervix
The lower part of the uterus that connects the uterus to the vagina. It has a small opening that allows menstrual blood to pass from the uterus into the vagina. During childbirth, the cervix opens wider to allow a baby to pass from the uterus into the vagina.
E
Ectopic Pregnancy
A pregnancy that occurs when a fertilized egg implants outside the uterus, most often in a fallopian tube. An ectopic pregnancy cannot develop normally and can become life-threatening. It requires medical care.
Estrogen
A hormone produced mainly by the ovaries that plays a role in female reproductive development, including breast development. During the menstrual cycle, rising estrogen helps the uterine lining build in preparation for a possible pregnancy.
F
Fallopian Tubes
Two tubes in the female reproductive system that carry eggs from the ovaries toward the uterus. Fertilization can occur in a fallopian tube if sperm is present.
Fertility
The ability to become pregnant and have a baby.
Follicular Phase
The phase of the menstrual cycle that begins on the first day of menstruation and ends with ovulation. During this phase, follicles containing immature eggs develop in the ovaries, and one usually becomes the dominant follicle from which an egg is released during ovulation.
H
Hormones
Chemical messengers made by glands and other tissues in the body that help control many body functions. Reproductive hormones, including estrogen and progesterone, help regulate the menstrual cycle and play an important role in the changes that occur throughout our reproductive lives.
L
Luteal Phase
The phase of the menstrual cycle that begins after ovulation and continues until the next menstrual period begins. During this phase, progesterone rises and helps prepare and maintain the uterine lining for the possibility of pregnancy.
M
Menopause
The point when menstrual periods have permanently stopped and pregnancy is no longer possible naturally. Menopause is reached after 12 consecutive months without a menstrual period, when there is no other medical reason for the periods to have stopped. Menopause most commonly occurs between ages 45 and 55.
Menstrual Cramps
Pain or cramping in the lower abdomen that can occur just before or during a menstrual period as the uterus contracts to help shed its lining. Menstrual cramps can range from mild discomfort to pain that interferes with everyday activities.
Menstrual Cycle
The series of changes the reproductive system goes through to prepare for the possibility of pregnancy. The cycle begins on the first day of menstruation and continues until the next menstrual period begins.
Menstruation
The process when the uterus sheds its lining if pregnancy does not occur. The blood and tissue from the uterine lining leave the body through the vagina. Menstruation is also commonly called a period.
O
Ovarian Follicles
Small, fluid-filled sacs in the ovaries that contain immature eggs. During the menstrual cycle, follicles develop and one usually becomes the dominant follicle from which an egg is released during ovulation.
Ovaries
Two organs in the reproductive system that contain eggs and produce hormones, including estrogen and progesterone. During ovulation, an ovary releases an egg, which moves into a fallopian tube.
Ovulation
The release of an egg from a follicle in an ovary. After its release, the egg moves into a fallopian tube, where it may be fertilized if sperm is present.
P
Pelvic Inflammatory Disease (PID)
An infection of the reproductive organs. PID is often caused by sexually transmitted infections (STIs), but other types of bacteria can also cause it. If left untreated, PID can lead to serious problems, including infertility, ectopic pregnancy, and long-term pelvic pain.
Perimenopause
The transition leading to menopause when hormone levels begin to fluctuate, causing changes in the menstrual cycle. These changes may include cycles that are longer or shorter than usual, heavier or lighter bleeding, or skipped periods. Other symptoms may include hot flashes and trouble sleeping. There is no specific age when perimenopause begins; it may start as early as the 30s or as late as the 50s. Perimenopause ends after 12 consecutive months without a menstrual period, when menopause is reached.
Progesterone
A hormone produced mainly by the ovaries that helps prepare and maintain the uterine lining for a possible pregnancy. If pregnancy occurs, progesterone helps maintain the lining during early pregnancy.
U
Uterine Lining
The inner lining of the uterus that changes throughout the menstrual cycle. It builds in preparation for the possibility of pregnancy. If pregnancy does not occur, the lining sheds, causing menstrual bleeding, and begins building again during the next cycle.
Uterus
A muscular, pear-shaped organ located in the pelvis. The uterus plays an important role throughout the menstrual cycle, including building and shedding the uterine lining. The shedding of this lining is what causes menstrual bleeding.
V
Vagina
A muscular canal that extends from the cervix to the outside of the body. Menstrual blood passes through the vagina as it leaves the body. During childbirth, a baby passes through the vagina to be born.
Vaginal Discharge
Fluid and cells that leave the vagina and help keep it clean and healthy. Vaginal discharge usually begins around puberty and can change in amount, color, and thickness throughout the menstrual cycle.