Postnatal Changes in Testicular Position Are Associated With IGF-I and Function of Sertoli and Leydig Cells.

CONTEXT

Despite clinical guidelines calling for repetitive examination of testicular position during childhood, little is known of normal changes in testicular position during childhood, let alone factors that control it.

OBJECTIVE

To assess changes in and factors associated with testicular position during childhood.

DESIGN

Testicular position (the distance from the pubic bone to the upper pole of the testes) at birth, 3 months, 18 months, 36 months, and 7 years and reproductive hormones at 3 months were measured.

SETTING

Prenatally recruited, prospective longitudinal birth cohort.

PARTICIPANTS

A total of 2545 boys were recruited prenatally in a Danish-Finnish birth cohort and had a testicular position examination available. A subset of 680 Danish and 362 Finnish boys had serum reproductive hormone concentrations and insulin-like growth factor I (IGF-I) determined at 3 months.

MAIN OUTCOME MEASURES

Testicular distance to pubic bone (TDP), serum reproductive hormone, and IGF-I concentrations.

RESULTS

TDP increased from birth to 3 months and decreased thereafter. Length, gestational age, weight for gestational age, and penile length were positively associated with larger TDP and thus lower testicular position in a linear mixed-effect model. Furthermore, IGF-I concentration, inhibin B/follicle-stimulating hormone ratio, and testosterone/luteinizing hormone ratio were all independently and positively associated with longer TDP.

CONCLUSIONS

We provide longitudinal data on postnatal changes in TDP. TDP is dynamic and associated with Leydig and Sertoli cell function as well as with IGF-I levels during the first months of life at mini-puberty of infancy. TDP may thus be a useful biomarker of postnatal testicular function.