Anogenital distance (AGD) is the distance from the midpoint of the

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

to the

genitalia A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, ...

, the underside of the

vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hy ...

, the

clitoris The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), above the o ...

or the

scrotum The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum co ...

. It is considered medically significant for a number of reasons, in both humans and other animals, including sex determination and as a marker of

endocrine disruptor Endocrine disruptors, sometimes also referred to as hormonally active agents, endocrine disrupting chemicals, or endocrine disrupting compounds are chemicals that can interfere with endocrine (or hormonal) systems. These disruptions can cause ...

exposure. It is regulated by

dihydrotestosterone Dihydrotestosterone (DHT, 5α-dihydrotestosterone, 5α-DHT, androstanolone or stanolone) is an endogenous androgen sex steroid and hormone. The enzyme 5α-reductase catalyzes the formation of DHT from testosterone in certain tissues incl ...

, which can be disrupted by

phthalate Phthalates (, ), or phthalate esters, are esters of phthalic acid. They are mainly used as plasticizers, i.e., substances added to plastics to increase their flexibility, transparency, durability, and longevity. They are used primarily to soften ...

s common in plastics. The ''anogenital index'' (AGI) is an index used to compare the AGD relative to a model based on body weight. It is computed as the AGD divided by weight GI = AGD/weight (mm/kg)

Measurement

The AGD is usually measured as follows: from the center of the

to the posterior convergence of the fourchette (where the vestibule begins) in females (AGD-AF); and from the center of the

to the junction of the smooth perineal skin with the rugate skin of the

in males (AGD-AS). An alternative measurement, AGD-AC, defined only in females, is measured from the anus to the clitoris.

In humans

Early studies showed that the human

perineum The perineum in humans is the space between the anus and scrotum in the male, or between the anus and the vulva in the female. The perineum is the region of the body between the pubic symphysis (pubic arch) and the coccyx (tail bone), inclu ...

was twice as long in males as in females, but it has since been found to be three quarters the male distance in females, although males have more variance. Measuring the anogenital distance in neonatal humans has been suggested as a noninvasive method to determine male feminisation and female

virilization Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens. Virilization is most commonly used in three medical and biology ...

and thereby predict neonatal and adult reproductive disorders. A study by Swan et al. determined that the AGD is linked to fertility in males, and penis size. * Males with a short AGD (lower than the median around 52 mm (2 in)) have seven times the chance of being sub-fertile as those with a longer AGD. It is linked to both semen volume and sperm count. A lower than median AGD also increases the likelihood of undescended testes, and lowered sperm counts and testicular tumors in adulthood. Babies with high total exposure to

phthalates Phthalates (, ), or phthalate esters, are esters of phthalic acid. They are mainly used as plasticizers, i.e., substances added to plastics to increase their flexibility, transparency, durability, and longevity. They are used primarily to softe ...

were ninety times more likely to have a short AGD, despite not every type of the nine phthalates tested being correlated with shorter AGD. Swan et al. report that the levels of phthalates associated with significant AGD reductions are found in approximately one-quarter of Americans tested by the

Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...

(CDC) for phthalate body burdens. Women who had high levels of phthalates in their urine during pregnancy gave birth to sons who were ten times more likely to have shorter than expected AGDs. A 2018 study by Barrett et al. found that infant girls born to women with

polycystic ovary syndrome Polycystic ovary syndrome, or PCOS, is the most common endocrine disorder in women of reproductive age. The syndrome is named after the characteristic cysts which may form on the ovaries, though it is important to note that this is a sign and n ...

(PCOS) had longer AGD, suggesting higher fetal

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteris ...

exposure, than girls born to women without PCOS.

Conditions

Hypospadias Hypospadias is a common variation in fetal development of the penis in which the urethra does not open from its usual location in the head of the penis. It is the second-most common birth abnormality of the male reproductive system, affecting abo ...

and

cryptorchidism Cryptorchidism, also known as undescended testis, is the failure of one or both testes to descend into the scrotum. The word is from Greek () 'hidden' and () 'testicle'. It is the most common birth defect of the male genital tract. About 3% of ...

are conditions which may be induced in males with short AGD. Other problems in males include risk of testicular dysgenesis syndrome.

In other animals

There have been extensive studies of AGD effects on animals. In some animals it is routinely measured to determine health. Experiments have demonstrated that in rodent studies this distance is shortened when the mother is exposed to chemicals that are anti-androgenic, such as

dibutyl phthalate Dibutyl phthalate (DBP) is an organic compound which is commonly used as a plasticizer because of its low toxicity and wide liquid range. With the chemical formula C6H4(CO2C4H9)2, it is a colorless oil, although commercial samples are often yel ...

(DBP) or

benzyl butyl phthalate Benzyl butyl phthalate (BBP) is an organic compound historically used a plasticizer, but which has now been largely phased out due to health concerns. It is a phthalate ester of containing benzyl alcohol, and ''n''-butanol tail groups. Like mo ...

(BBzP).

Bisphenol A Bisphenol A (BPA) is a chemical compound primarily used in the manufacturing of various plastics. It is a colourless solid which is soluble in most common organic solvents, but has very poor solubility in water. BPA is produced on an industrial ...

in certain doses increases the AGD of both genders of a study on mice. In 2017, Gobikrushanth et al. studied the relationship between AGD (the distance from the center of the anus to the base of the vagina and the clitoris) and fertility in Canadian Holstein cows. They found that in first and second parity cows an increase in AGD has an inverse correlation with pregnancy success after first artificial insemination. This correlation was not found in third+ parity cows.

References

{{reflist Mammal anatomy fr:Périnée#Distance ano-génitale

Measurement

In humans

Conditions

In other animals

See also

References