Anogenital distance (AGD) is the distance from the anus to the genitalia, the base of the penis or vagina. It is considered medically significant for a number of reasons, in both humans and animals. It is regulated by dihydrotestosterone, which can be disrupted by phthalates common in plastics. Such endocrine disruption may affect the development of the brain.
Studies show that the human perineum is twice as long in males as in females, but males have more variance. Measuring the anogenital distance in neonatal humans has been suggested as a noninvasive method to determine male feminisation and thereby predict neonatal and adult reproductive disorders.
A study by Swan et al. determined that the AGD is linked to fertility in males, not penis size. Males with an abnormally 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 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 (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.
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 (DBP) or benzylbutyl phthalate (BBzP).
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- Welsh, Michelle et al. (13 March 2008). "Identification in rats of a programming window for reproductive tract masculinization, disruption of which leads to hypospadias and cryptorchidism". Journal of Clinical Investigation.
- Swan, Shanna H. et al. (August 2005). "Decrease in Anogenital Distance among Male Infants with Prenatal Phthalate Exposure". Environmental Health Perspectives 8 (113): 1056–1061. Retrieved 2011-08-24. Lay summary – OurStolenFuture.org: Swan et al., "Decrease in Anogenital Distance among Male Infants with Prenatal Phthalate Exposure".
- Zabarenko, Deborah (4 April 2011). "Key genital measurement linked to male fertility". Reuters. Retrieved 2011-08-24.
- Hsieh MH, Breyer BN, Eisenberg ML, Baskin LS (March 2008). "Associations among hypospadias, cryptorchidism, anogenital distance, and endocrine disruption". Current Urology Report 2 (9): 137–142. PMID 18419998.
- Jain VG, Singal AK (September 2013). "Shorter anogenital distance correlates with undescended testis: a detailed genital anthropometric analysis in human newborns.". Human Reproduction 9 (28): 2343–9. doi:10.1093/humrep/det286. PMID 23838161.
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- Swan, S.; Main, K.; Liu, F.; Stewart, S.; Kruse, R.; Calafat, A.; Mao, C.; Redmon, J.; Ternand, C.; Sullivan, S.; Teague, J. L.; Study for Future Families Research Team (2005). "Decrease in anogenital distance among male infants with prenatal phthalate exposure". Environmental health perspectives 113 (8): 1056–1061. doi:10.1289/ehp.8100. PMC 1280349. PMID 16079079.