progesterone
Meaning of progesterone: Its rise and fall runs the second half of the cycle, and a well-timed measurement says whether ovulation happened at all.
Definition of progesterone
Progesterone is a steroid hormone that prepares and maintains the lining of the uterus. After ovulation the emptied follicle becomes a structure called the corpus luteum and releases it in quantity; if pregnancy follows, the placenta takes over production. Falling levels at the end of a cycle bring on menstruation. Small amounts also come from the adrenal glands in both sexes.
What does it do across the menstrual cycle?
The first half of the menstrual cycle belongs to estrogen, which thickens the uterine lining. Progesterone takes over after ovulation and converts that thickened lining into a receptive, secretory surface an embryo could implant into. It also thickens cervical mucus, quiets contractions of the uterine muscle and raises resting body temperature slightly, which is the basis of temperature-based cycle tracking. If no embryo implants, the corpus luteum fades after about a fortnight, progesterone falls, and the lining is shed. If implantation does occur, signals from the early pregnancy keep the corpus luteum alive until the placenta can produce enough on its own.
How do progesterone and progestins differ?
| Progesterone | Progestins | |
|---|---|---|
| What it is | The hormone the body itself makes | Synthetic relatives, chemically altered |
| Why altered | Broken down rapidly if swallowed plain | Survive digestion, last longer, act more strongly |
| Typical use | Supporting the lining in fertility treatment, hormone therapy | Contraception, including the birth control pill, and control of heavy bleeding |
Progestins are not interchangeable with one another either, since each has its own pattern of effects on other steroid receptors.
Why is it measured?
A blood level drawn in the second half of the cycle is the standard way to confirm that ovulation occurred, since the rise only happens once a follicle has released its egg. Levels are also followed early in pregnancy alongside other markers. One source of confusion is worth separating out: a progesterone receptor test on breast cancer tissue measures nothing about hormone levels in the blood. It reports whether the tumor cells carry receptors for the hormone, which is a property of the tumor.
Used in a sentence
Progesterone levels were measured as part of the evaluation of the patient's menstrual irregularity.
Good to know
Progesterone and synthetic progestins are related but not equivalent, and each progestin has its own pattern of activity, so findings about one cannot be assumed to apply to another.
Word origin
Where “progesterone” comes from
Formed from pro-, Latin for in support of, and gestation, from Latin gestare, meaning to carry, with the chemical ending -one marking it as a steroid ketone.