The prevalence of cryptorchidism in newborn term infants is 2% to 8% worldwide.[3]Virtanen HE, Bjerknes R, Cortes D, et al. Cryptorchidism: classification, prevalence and long-term consequences. Acta Paediatr. 2007 May;96(5):611-6.
https://onlinelibrary.wiley.com/doi/full/10.1111/j.1651-2227.2007.00241.x
http://www.ncbi.nlm.nih.gov/pubmed/17462053?tool=bestpractice.com
[4]Sijstermans K, Hack WW, Meijer RW, et al. The frequency of undescended testis from birth to adulthood: a review. Int J Androl. 2008 Feb;31(1):1-11.
https://www.doi.org/10.1111/j.1365-2605.2007.00770.x
http://www.ncbi.nlm.nih.gov/pubmed/17488243?tool=bestpractice.com
This decreases to 1% to 2% after the first few months of life, because congenital cryptorchidism may spontaneously resolve with the neonatal peak of testosterone by 3 months.[5]Brucker-Davis F, Pointis G, Chevallier D, et al. Update on cryptorchidism: endocrine, environmental and therapeutic aspects. J Endocrinol Invest. 2003 Jun;26(6):575-87.
http://www.ncbi.nlm.nih.gov/pubmed/12952375?tool=bestpractice.com
[6]Kuiri-Hänninen T, Koskenniemi J, Dunkel L, et al. Postnatal testicular activity in healthy boys and boys with cryptorchidism. Front Endocrinol (Lausanne). 2019;10:489.
https://www.doi.org/10.3389/fendo.2019.00489
http://www.ncbi.nlm.nih.gov/pubmed/31396156?tool=bestpractice.com
In northern England, prevalence was recently reported as 7.6 per 1000 male live births, with an orchiopexy rate of 1.8 per 1000 males ages 0 to 4 years.[7]Abdullah NA, Pearce MS, Parker L, et al. Birth prevalence of cryptorchidism and hypospadias in northern England, 1993-2000. Arch Dis Child. 2007 Jul;92(7):576-9.
http://www.ncbi.nlm.nih.gov/pubmed/17142312?tool=bestpractice.com
There is controversy regarding reports of increasing incidence potentially due to endocrine disruption/environmental exposures, and more studies are needed to prove or disprove this hypothesis.[5]Brucker-Davis F, Pointis G, Chevallier D, et al. Update on cryptorchidism: endocrine, environmental and therapeutic aspects. J Endocrinol Invest. 2003 Jun;26(6):575-87.
http://www.ncbi.nlm.nih.gov/pubmed/12952375?tool=bestpractice.com
[8]Vidaeff AC, Sever LE. In utero exposure to environmental estrogens and male reproductive health: a systematic review of biological and epidemiologic evidence. Reprod Toxicol. 2005 May-Jun;20(1):5-20.
http://www.ncbi.nlm.nih.gov/pubmed/15808781?tool=bestpractice.com
Two-thirds of cases are unilateral, while the remainder are bilateral.