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Physiology, Sexual Maturity Rating

Physiology, Sexual Maturity Rating

Article Author:
Jean Claude Guidi
Article Editor:
Amit Sapra
9/11/2020 8:23:48 PM
For CME on this topic:
Physiology, Sexual Maturity Rating CME
PubMed Link:
Physiology, Sexual Maturity Rating


The onset of and successful progression through puberty carries significant implications for an adolescent’s development with puberty radically altering a child’s physical, psychological, and social baseline. Puberty depends on the proper development of both the Hypothalamic-Pituitary-Gonadal (HPG) Axis and the Adrenal Axis. Hormones from these sources result in observable changes. In 1962, James M. Tanner developed the Sexual Maturity Rating Scale (SMR).[1] This scale, also known as the Tanner stages, granted providers objective criteria to monitor an adolescent’s progression through puberty. By evaluating the development of the testes, breast tissue, and pubic hair, a clinician can counsel and manage their patients through this critical period appropriately. 

Issues of Concern

It is crucial to understand the limitations of SMR when evaluating patients. SMR only measures the external signs of sexual development obtained via physical exam, and this can limit their use in non-clinical settings. [2] Additionally, the time of onset and rapidity of sexual maturity varies among different ethnicities. There is evidence of advancement in the timing of sexual maturation among a variety of populations; this is observable within both developed and underdeveloped societies, and the underlying cause remains unidentified. However, it is highly likely to be a multifactorial issue that relies on both social and physiological components. It is imperative to have recent and reliable data from a similar population subset to evaluate a patient properly using the SMR.[3][4]


The onset of puberty in both males and females relies on the hypothalamus. The intermittent release of GnRH from the hypothalamus, also known as the hypothalamic pulse generator, signals the release of LH and FSH from the anterior pituitary. There is a postulate that neurotransmitters GABA and Kisspeptin inhibit the release of GnRH. As an individual matures, the hypothalamus becomes less sensitive to this inhibition and eventually shifts towards pulsatile surges.[5][6]

In males, LH stimulates Leydig cells within the testes to produce testosterone, typically occurring between ages 9 to 14. Testosterone can then be converted into its more potent counterpart, dihydrotestosterone (DHT) peripherally via the 5-alpha-reductase enzyme. Testosterone acts on intracellular androgen receptors. It is responsible for the pubertal growth spurt, closure of the epiphyseal plates, deepening of the voice, penile and testicular enlargement, muscle growth, and libido. DHT acts similarly on intracellular receptors yet contributes to facial hair growth, sebaceous gland secretion, and male pattern baldness. 5-alpha-reductase inhibitors have become first-line therapy for the treatment of male pattern baldness.[7][8]

In females, both LH and FSH contribute to the development of secondary sexual characteristics. FSH promotes follicular maturation within the ovary. Theca cells within the follicle are responsive to LH surges releasing testosterone into the periphery. Adjacent granulosa cells, stimulated by FSH, convert testosterone to estrogen via aromatase. Estrogen then goes on to act on intracellular receptors within various tissues resulting in growth spurts, closure of the epiphyseal plates, genital enlargement, and breast tissue development.[9][10]

Puberty is also marked by increased adrenal androgen production, a period called adrenarche. Adrenarche typically occurs around age six. While a specific signaling molecule has to date eluded researchers, it results from increased androgen producing enzymes within the zona reticularis (ZR) layer of the adrenal gland. Dehydroepiandrosterone (DHEA) acts on intracellular receptors promoting androgen-dependent hair growth. Adrenarche is a common pathway between both sexes resulting in shared pubic hair growth patterns.[11]

Organ Systems Involved


Breast tissue development in the female marks the first secondary characteristic to develop in puberty. Free estrogen acts on intracellular receptors to promote the development of both ductal and stromal elements. The fatty stromal elements compose the majority of breast growth during puberty, and by its completion, there is still only a minor amount of ductal tissue present within the breast. Pregnancy and its associated hormonal changes result in the progression towards increased ductal tissue versus stroma.[12]


In males, the growth of the testes beyond 4 mL marks the onset of puberty. Testosterone not bound to either albumin or sex hormone-binding globulin (SHBG) acts on intracellular receptors resulting in increased DNA transcription. It is the rapid expansion of the seminiferous tubules and an increase in germ cell number that contributes to testicular growth patterns.[13][14][7]

Pubic Hair

DHEA and DHEAS both result in the production of pubic and axillary hair growth. These hormones act on follicles, causing both thickening and darkening of the resultant hair. The distribution of hair follicles highly responsive to these hormones is genetically determined. Thus, individuals may be predisposed to a greater distribution of darkened body hair.[15]

Related Testing

Alternative methods have been developed to assess a patient’s pubertal development. The pubertal development scale (PDS) is a questionnaire that covers typical changes manifested throughout puberty (e.g., growth spurt, body hair growth, voice deepening, etc.) and asks patients to answer whether they’ve experienced these changes or not. Features not assessed with SMR can be evaluated through this system. Additionally, it allows for the assessment of a patient’s understanding of their progression through puberty.[16]

Picture-based Interview about Puberty (PBIP) is similar to SMR but relies on the patient to indicate which image most correlates to their current stage of development.[2]


Precocious Puberty

Premature activation of the HPG axis underlies the etiology of precocious puberty. Pubertal characteristics with onset before age 8 in girls and 9 in boys is the defining characteristic. The cause is currently unknown. However, congenital malformations and acquired insults have both merited consideration as potential etiologies.[17]

Delayed Puberty

Delayed Puberty is a condition most often cited in males. It results in delayed skeletal maturation compared to individuals within the same population. A diagnosis of exclusion delayed puberty commonly resolves without issue and can be seen amongst familial generations. Proper counseling of patients is imperative as delayed puberty can result in potential stigma among their peers. To exclude other causes of delayed maturation, such as hypogonadism, is very important, as these conditions require pharmacologic treatment.


Male and Female Hypogonadism results from the underproduction of their respective hormonal counterpart. Proper diagnosis requires a full history, physical exam, and laboratory evidence. 

Male hypogonadism refers to symptomatology secondary to the underproduction of testosterone with a proper formation of spermatozoa. With testosterone playing a pivotal role in growth spurts, facial hair growth, penile elongation, and testicular enlargement, a deficiency can result in underdevelopment in these areas. The two subsets, primary and secondary, result from pathology in either the testicles or the Hypothalamus/Pituitary, respectively.[18]

Female hypogonadism results from dysfunction within the hypothalamic-pituitary-ovarian axis. Whether this dysfunction is acquired or congenital, the primary manifestation is menstrual cycle disturbances. However, underdevelopment of breast tissue can also occur.[19]

Precocious puberty, delayed puberty, and hypogonadism all require evaluation with a pediatric endocrinologist. Hormonal therapy allows for halting or the initiation of puberty depending on the presentation and is the mainstay of treatment.[20]

Clinical Significance

SMR grants providers a lens through which to evaluate and counsel patients through puberty. A patient’s age of pubertal onset estimated final height, and potential environmental exposures can all correlated through proper physical examination and SMR.[21] 

Listed below are the criteria of the Sexual Maturity Rating Scale.

It is crucial to keep in mind the hormonal axes that contribute to the development of each examined aspect. When examining males, long bone growth, deepening of the voice, and facial hair all rely on gonadal hormones. When examining females, long bone growth, breast enlargement, and the onset of menarche also rely on gonadal hormones. Pubic and body hair both rely on adrenal hormones.[2] Thus, inconsistencies within a particular subset of the SMR allow for a focused examination of the adrenal axis versus the HPG axis. 

Sexual Maturity Rating:     

Pubic Hair Scale: (both males and females)

  • Stage 1: Absent hair
  • Stage 2: Downy hair present
  • Stage 3: Scant terminal hair present
  • Stage 4: Terminal hair that fills the whole triangle overlaying the pubic area
  • Stage 5: Terminal hair extending beyond the inguinal crease onto the thigh area

Female Breast Development Scale[22]:

-Stage 1: No glandular breast tissue palpable

-Stage 2: Breast bud palpable under the areola (1st pubertal sign in females)

-Stage 3: Breast tissue palpable outside areola; no development of areola

-Stage 4: Areola elevated above the contour of the breast, forming “double scoop” appearance

-Stage 5: Areolar mound recedes into single breast contour along with hyperpigmentation of areola, papillae development, and nipple protrusion

When evaluating Testicular volumes, ultrasound measurements are the gold standard. However, this method may be inconvenient, cost-prohibitive, or inaccessible. While examinations with a centimeter ruler or orchidometer are often performed, these methods result in inaccuracies.

Male External Genitalia Scale[23]:

  • Stage 1: Testicular volume less than 4 ml or long axis less than 2.5 cm
  • Stage 2: 4 ml to 8 ml (or 2.5 to 3.3 cm long), 1st pubertal sign in males
  • Stage 3: 9 ml to 12 ml (or 3.4 to 4.0 cm long)
  • Stage 4: 15 to 20 ml (or 4.1 to 4.5 cm long)
  • Stage 5: greater than 20 ml (or over 4.5 cm long)


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