Micropenis is a term used to describe a penis that is 2.5 standard deviations smaller than the mean average for the age and race for a man. This translates to a stretched penis length of fewer than 2-3/4 inches and an erect penis length of 5 inches. Statistically, micropenis occurs in 0.6 percent of the population, making it a rare characteristic. The term is most commonly used when all other structures of the genitals, including the scrotum, testicles, and perineum, are “normal.”
A micropenis develops during gestation and will often be the only physiological abnormality have noted in the pregnancy. One of the possible causes of this is the low production of human chorionic gonadotropin during the early part of the pregnancy. This is a hormone that stimulates the developing testes to produce testosterone.
After 14 weeks, penile growth falls under the influence of another hormone, known as luteinizing hormone, which also stimulates testosterone in the so-called Leydig cells of the testicles. If the production of either or both of these fetal hormones is impeded, the child’s penis length may be affected.
Genetics may also play a role. While there is no single gene that causes a micropenis, the condition is commonly linked to such chromosomal disorders as androgen insensitivity syndrome, Klinefelter syndrome, Turner syndrome, and Down syndrome.
There is also evidence that oestrogen-based fertility drugs like diethylstilboestrol may cause smaller than normal penis size if taken during early pregnancy. While environmental pollutants are a less common cause, some research suggests that exposure to chlorinated pesticides during pregnancy may cause micropenis and other genital abnormalities in male babies.
From a practical standpoint, micropenis may complicate urination by making it difficult to direct the stream. Many men will simply compensate for this by sitting on the toilet when urinating. On a more significant note, penis sizes of less than two inches are associated with a lower likelihood of conception. Moreover, some men with a micropenis will have a low sperm count as the result of an underlying pituitary disorder. In such cases, assisted reproductive techniques are available to significantly improve one’s chances of conceiving.