Context: Hormonal dysregulation has been suggested to be one of many etiological factors of cryptorchidism.

Objectives: to assess the hypothalamic-pituitary-testicular axis in cryptorchid boys during the postnatal hormonal surge

Design: prospective, longitudinal, population-based

Setting: Two primary obstetric centers

Participants: 388 Finnish, 433 Danish boys (88 and 34 with cryptorchidism, respectively)

Interventions: clinical examinations at 0 and 3 months, blood samples at 3 months

Main outcome measures: testis position, reproductive hormones

Results: Finnish cryptorchid boys had significantly higher FSH (1.59 [0.50-3.53] vs. 1.30 [0.49-2.92] IU/l, P < 0.0001) and lower inhibin B (426 (254-770) vs. 459 (266-742) pg/ml, P < 0.015) levels than Finnish control boys (median, [2.5^th -97.5^th percentiles]). Danish cryptorchid boys had higher FSH levels than controls (1.47 [0.54-3.89] vs. 1.18 [0.41-3.04] IU/l, P = 0.018). Inhibin B levels in healthy Danish boys were lower than in Finnish (380 (233-637) pg/ml, P < 0.0001) and not reduced in Danish cryptorchid boys (392 (236-672) pg/ml, P = 0.851). Changes in hormone levels were strongest in boys with severe, persistent cryptorchidism, but also detectable in mild and transient cryptorchidism. Effects on Leydig cell function were subtle with increase of LH in Finnish (but not Danish) cryptorchid boys vs. controls (1.97 [0.77-5.91] vs. 1.75 [0.58-4.04] IU/l, P < 0.021), but testosterone levels remained within normal range.

Conclusions: Our results support the hypothesis that cryptorchidism is associated with a primary testicular disorder, which could be a cause or consequence of cryptorchidism. This malfunction is reflected by a low inhibin B production in the Finnish cohort and a high gonadotropin drive in both the Finnish and Danish cohorts.