Abstract

Objective: To evaluate the association between birth weight (BW), childhood and adolescent BMI, with reproductive capacity in men.

Design: A prospective, population-based cohort study (Northern Finland birth cohort 1966).

Methods: 6196 men born in 1966 followed from birth to age 50 years. Weight and height were measured repeatedly by professionals. Reproductive capacity (infertility assessment, male factor infertility and infertility treatment by age 46 years) was evaluated by questionnaires at ages 31 and 46 years. Number of children by age 50 years was recovered from registers. After excluding the men who reported never having attempted to have children or not answering the question at age 31 or 46 years (n=2041), 4128 men were included into the final study population. Results were adjusted for BW, BW for gestational age (GA), mother’s smoking status, marital status, educational level and smoking status.

Results: Being small for GA (10.5% vs.8.2%, p=0.012) or having a lower BW (3495g vs.3548g, p=0.003) associated with childlessness. The association was however no longer significant after adjusting for marital status. Being underweight in early childhood was associated with an increased risk of infertility assessment (adjusted, aOR:2.04(1.07‐3.81)) and childlessness (aOR:1.47(1.01‐2.17)) compared to the normal weight group. Conversely, overweight or obesity in early childhood was associated with a decreased risk of infertility assessment (aOR:0.60(0.41‐0.87)), treatment (aOR:0.42(0.25‐0.70)) and male factor infertility (aOR:0.45(0.21‐0.97)). BMI in mid-childhood or puberty had no association with infertility or childlessness.

Conclusion: In boys, an optimal growth trajectory during pregnancy and during early childhood seems to be very important for life-long fertility.