Men born small for gestational age or with low birth weight do not improve their rate of reproduction over time: a Swedish population-based study.

Objective: To investigate whether the reduced reproductive rate among men born small for gestational age (SGA) or with low birth weight (LBW) is present after up to 44 years of follow-up.

Design: Population-based register study.

Setting: National registers in Sweden.

Patient(s): All men born in Sweden between 1973 and 1993 (n = 1,045,167) followed up to 2018.

Intervention(s): None.

Main Outcome Measure(s): Registered fatherhood, infertility diagnoses, and fertility treatments obtained from registers up to 2018 RESULT(S): Men born SGA or with LBW have a lower chance of becoming fathers than men born with normal birth characteristics: hazard ratio (95% confidence interval) 0.91 (0.90-0.92) and 0.88 (0.86-0.90), respectively. The reduction in reproductive rate is more evident after a longer follow-up time. Men born SGA were more likely to receive a diagnosis of infertility. Sperm donation and intracytoplasmic sperm injection were more often used in men born SGA, further strengthening the hypothesis of an association between birth characteristics and male infertility.

Conclusion(s): Men born SGA or with LBW have a lower chance of becoming fathers, but the reduction in fertility is smaller for the younger cohort. Further studies are needed to determine if this difference is maintained.