Classification of Progesterone
Progesterone is classified as a naturally occurring steroid hormone that serves as an essential reproductive hormone and steroidogenic precursor for other hormones including aldosterone, cortisol, estradiol, and testosterone. 1
Biochemical Classification
Steroid hormone structure: Progesterone belongs to the steroid hormone family, characterized by its four-ring carbon structure typical of all steroid compounds 2, 1
Endogenous vs. synthetic forms: The term "progesterone" should only be used for the natural hormone produced by the ovaries or included in registered drugs, distinguishing it from synthetic progestogens 3
Physiological Classification
Reproductive hormone: Progesterone is traditionally classified as "the pregnancy hormone" due to its essential role in menstrual cycle regulation, implantation, and pregnancy maintenance 4, 5
Steroidogenic precursor: Beyond reproduction, progesterone functions as a key precursor molecule in the biosynthesis of other critical steroid hormones throughout the body 1
Functional Classification by Mechanism
Progesterone exerts its effects through multiple mechanisms:
Myometrial relaxation: Reduces uterine contractility by decreasing prostaglandin synthesis, infection-mediated cytokine production, and changing progesterone receptor expression to maintain a non-contractile uterine state 6
Immunomodulatory agent: Modulates maternal immune response and suppresses inflammatory responses at the decidual level 4
Cervical barrier function: Alters cervical stromal degradation and creates a barrier to ascending infection 7
Therapeutic Classification
In clinical practice, progesterone formulations are classified by route of administration:
Intramuscular preparations: 17-alpha-hydroxyprogesterone caproate (17P) 250 mg weekly is the recommended formulation for prevention of recurrent preterm birth in singleton pregnancies with prior spontaneous preterm birth 8, 7, 9
Vaginal preparations: Available as 90-mg gel, 100-mg suppositories, or 200-mg suppositories for luteal phase support and prevention of preterm birth in women with short cervical length 8, 7, 9
Oral preparations: Natural micronized progesterone is preferred for hormone replacement therapy in premature ovarian insufficiency due to favorable cardiovascular and thrombotic risk profiles 8
Clinical Context Classification
Effective indications where progesterone demonstrates proven benefit:
- Prevention of recurrent preterm birth in singleton pregnancies with prior spontaneous preterm birth (20-36 6/7 weeks) using 17P 8, 7, 9
- Prevention of preterm birth in singleton pregnancies with short cervical length ≤20 mm at ≤24 weeks using vaginal progesterone 8, 7, 9
- Luteal phase support in assisted reproductive technology 5, 3
Ineffective indications where progesterone should NOT be used: