Context: Concern has been raised for the health of the offspring conceived by assisted reproduction technologies. Basal reproductive hormones around three months of age reflect the pituitary-testicular axis, which is transiently active at this age.

Objectives: We tested the hypothesis that transmission of impaired testicular function from father to son could be detected at three months of age in boys conceived by Intra-Cytoplasmic Sperm Injection (ICSI), which is predominantly used in management of male infertility.

Design: A longitudinal prospective cohort study including 125 boys conceived by ICSI, 124 boys conceived by In-Vitro Fertilisation (IVF) and 933 naturally conceived (NC) boys.

Intervention: Anthropometrical measurements at birth and at 3 months of age and 58, 67 and 64% of ICSI, IVF and NC boys, respectively, had a blood sample taken at 3 months.

Main outcome measures: Serum levels of Luteinizing hormone (LH), Follicle stimulating hormone (FSH), Sex hormone binding globulin (SHBG), Inhibin B, testosterone as well as penile length.

Results: Serum testosterone levels were significantly lower in boys conceived by ICSI (2.4 nmol/l; 0.2 - 4.9 nmol/l) (median; 2.5-97.5 percentiles) compared to NC boys (3.3 nmol/l; 0.6 - 7.6 nmol/l), p<0.001, and the LH/testosterone ratio was increased (0.8; 0.2 - 7.9) versus (0.5; 0.2 - 2.3), respectively, p=0.001. Boys conceived by IVF because of female infertility factors had a normal serum testosterone and LH/testosterone ratio compared to controls. Adjusted analyses for confounders did not alter the results.

Conclusion: Our results point towards a subtle impairment of Leydig cell function in boys conceived by ICSI, possibly inherited from their fathers. The clinical significance of our findings is uncertain. However, our findings should raise concern as ICSI is increasingly employed to overcome male infertility.