The prevalence of cryptorchidism in newborn term infants is 2% to 8% worldwide.[3]Virtanen HE, Toppari J. Epidemiology and pathogenesis of cryptorchidism. Hum Reprod Update. 2008 Jan-Feb;14(1):49-58.
https://academic.oup.com/humupd/article/14/1/49/823056
http://www.ncbi.nlm.nih.gov/pubmed/18032558?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
While only a few reliable prospective studies have been conducted to evaluate trends in cryptorchidism incidence, English research has produced some of the most relevant. The first study conducted in the early 1960s reported an incidence of 4.2% at birth and 0.97% at 3 months.[7]Scorer CG. The descent of the testis. Arch Dis Child. 1964 Dec;39:605-9.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2019243/pdf/archdisch01585-0073.pdf
http://www.ncbi.nlm.nih.gov/pubmed/14230757?tool=bestpractice.com
A few decades later a second study reported an incidence of 5.01% at birth and 1.78% at 3 months.[8]John Radcliffe Hospital Cryptorchidism Study Group. Cryptorchidism: a prospective study of 7500 consecutive male births, 1984-8. Arch Dis Child. 1992 Jul;67(7):892-9.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1793845/pdf/archdisch00636-0010.pdf
http://www.ncbi.nlm.nih.gov/pubmed/1355643?tool=bestpractice.com
In a third, more recent study, prevalence was reported as 7.6 per 1000 male live births, with an orchiopexy rate of 1.8 per 1000 males aged 0 to 4 years.[9]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
[10]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.