Average stretched Micropenis stretched
Age
length length
Newborn at 30
2.5 cm 1.5 cm
weeks
Newborn at 34
3.0 cm 2.0 cm
weeks
Newborn at full term 3.2 cm 2.4–2.5 cm
0–5 months 3.9 cm 1.9 cm
6–12 months 4.3 cm 2.3 cm
1–2 years 4.7 cm 2.6 cm
2–3 years 5.1 cm 2.9 cm
3–4 years 5.5 cm 3.3 cm
4–5 years 5.7 cm 3.5 cm
5–6 years 6.0 cm 3.8 cm
6–7 years 6.1 cm 3.9 cm
7–8 years 6.2 cm 3.7 cm
8–9 years 6.3 cm 3.8 cm
9–10 years 6.3 cm 3.8 cm
10–11 years 6.4 cm 3.7 cm
Adult 13.3 cm 9.3 cm
SPL for adults
In an adult, the average stretched penile length is about 13.24 cm (5.21 in.).
An adult micropenis is a stretched penile length of 9.32 cm (3.67 in.) or less.
Group Micropenis SPL measurement
Newborn babies <1.9 cm (0.75 in.)
Older, prepubescent boys <3.8 cm (1.5 in.)
Adult men <9.32 cm (3.67 in.)
The proper way to measure for a micropenis is to gently stretch it and
measure the length from the tip to the base, closest to the body.
Flaccid, stretched, and erect penile lengths (cm) in healthy adolescents (18)
Causes of micropenis (15)
Diagnostic Tests
Laboratory Tests
First-line tests include measurement of serum gonadotropins, testosterone, DHT, and
precursors of testosterone. Levels of other pituitary hormones may also be measured when
needed.
Endocrinologic assessment helps determine at what level the cause of micropenis is in the
hypothalamic-pituitary-testicular axis (9). In addition to evaluation of central endocrine
functions, testicular functions also need to be evaluated simultaneously. Hence, serum
testosterone levels are measured before or after administering hCG. This test is performed
by intramuscular administration of hCG in a dose of 1 000 units for 3 days, or 1 500 units every
two days for 14 days; testosterone levels below 300 ng/dL may indicate gonadal dysgenesis (26).
If LH and FSH levels are elevated, and there is no increase in testosterone levels following
administration, testicular insufficiency or absence should be considered. In addition, measuring
17 hydroxyprogesterone, dehydroepiandrosterone, and androstenedione levels before or after a
hCG stimulation test can reveal enzyme defects that play a role in testosterone synthesis.
Inhibin B and AMH, also known as Mullerian-inhibiting hormone are produced by functional
Sertoli cells, and determination of their blood levels can be used to detect the presence of
functional testicular tissue (9,27). Low levels of AMH, accompanied by normal inhibin B levels,
and a rare defect in the AMH gene, indicate persistent Mullerian duct syndrome (9).
Imaging Tests
Pelvic ultrasound can be used to visualize internal genital organs in suspicious cases. Magnetic
resonance imaging is used to investigate structural midline defects, such as pituitary stalk
dysplasia syndrome, central diabetes insipidus characterized by absence of the pituitary bright
spot in the posterior neurohypophysis, and pituitary dysplasia (9, 28). A small posterior pituitary
gland, thinned or disappeared pituitary stalk, and posterior pituitary ectopia are findings that may
indicate hypopituitarism, thus enabling determination of the etiology (28,29).
Genetic Tests
Some authors suggest karyotype assignment using chromosomal analysis or Y-fluorescence in
order to determine the sex. Genetic testing may be necessary to eliminate other syndromes (24).
Treatment Approaches
The goals of treatment for micropenis are to provide a body image that will not cause
embarrassment for the patient when seen by others, to enable the patient to have normal sexual
function, and also enable the patient to urinate standing up. Not exactly reaching the mean penile
length of the healthy population does not mean failure.
