title: Circannual rhythm in the incidence of cryptorchidism in Finland.
abstract: Conflicting data on circannual variation in birth rates of urogenital malformations have been reported previously. To assess risk factors of cryptorchidism we studied the seasonal variation of cryptorchidism in Finland. We performed a prospective cryptorchidism study in Turku, Finland, from 1997 to 2001 to evaluate the incidence of cryptorchidism. Clinical examinations were performed at birth and at 3 months. Of 9511 liveborn boys (1471 preterm boys) 216 (53 preterm boys) were cryptorchid at birth and 106 (19 preterm boys) at 3 months. The incidence of cryptorchidism was significantly higher in spring (February-April) (3.0%) than in summer (May-July) (1.7%) (OR 1.79; 95% CI: 1.23-2.63). This seasonal difference was observed both among preterm and term boys. We conclude that a circannual fluctuation in the incidence of cryptorchidism exists, which indicates an influence by environmental factors. The underlying reason for cyclicity affects similarly both preterm and term boys.
authors.affiliation: Department of Physiology, University of Turku, Kiinamyllynkatu 10, FIN-20520 Turku, Finland. marko.kaleva@utu.fi
authors.forename: Marko
authors.initials: M
authors.lastname: Kaleva
authors.forename: Helena E
authors.initials: HE
authors.lastname: Virtanen
authors.forename: Anne-Maarit
authors.initials: AM
authors.lastname: Haavisto
authors.forename: Katharina M
authors.initials: KM
authors.lastname: Main
authors.forename: Mikko
authors.initials: M
authors.lastname: Reunanen
authors.forename: Niels E
authors.initials: NE
authors.lastname: Skakkebaek
authors.forename: Jorma
authors.initials: J
authors.lastname: Toppari
mesh_terms: D002940:Circadian Rhythm; D003456:Cryptorchidism / Q000453:epidemiology*; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male