Chances of fathering a child slimmer for men born SGA, LBW

Men who are born small for gestational age (SGA) or with low birthweight (LBW) may be at a disadvantage when it comes to fertility or the prospect of becoming biological fathers, and this becomes more evident as men get older, according to a study.

In a cohort of men born in Sweden between 1973 and 1983, the reproductive rate is lower by approximately 10 percent for those born SGA and with LBW when analysed according to data up to 2006, the authors stated. Adding another 10 years of follow-up, the rate appears to be even lower.

“It could be speculated that the mechanisms lowering the chances of becoming a father become more evident with increasing age. The reasons for reproductive difficulties in men born preterm, SGA, or with LBW, apart from abnormalities in the genital system, might be the increased risks of neurologic dysfunction and psychologic morbidities seen in this group,” the authors explained. [Psychol Med 2015;45:985-999; BMC Pediatr 2010;10:91]

“[The said] difficulties might become more apparent with increasing age and could decrease a man’s chance of finding a partner, or they might even reduce a man’s wish to become a parent,” they added.

Of the 1,045,167 men included in the study, 515,040 were born between 1973 and 1983 and referred to as the older cohort while the remaining 530,127 were born between 1984 and 1993 and described as the younger cohort. By 2017, 68.8 percent and 24.9 percent of men in the respective cohorts had fathered children.

In the older cohort, significantly more men who remained childless had been born SGA (4.2 percent vs 3.6 percent; p<0.001), prematurely (4.5 percent vs 3.8 percent; p<0.001), or with LBW (2.5 percent vs 1.9 percent; p<0.001) as compared with men who had become fathers. The same trend was observed in the younger cohort, although the absolute differences were smaller (SGA: 2.4 percent vs 2.3 percent, p<0.001; preterm: 4.6 percent vs 4.4 percent, p=0.02; LBW: 2.2 percent vs 2.0 percent, p=0.01). [Fertil Steril 2021;doi:10.1016/j.fertnstert.2021.05.078]

Relationship-wise, more men in the younger than older cohort tended to be single, as did men who were born preterm, SGA, or with LBW vs those born with normal birth weight at term.

Cox proportional hazards analysis confirmed the relationship between being born SGA or with LBW and a lower likelihood of fathering children in the entire population (hazard ratios, 0.91, 95 percent confidence interval [CI], 0.90–0.92 and 0.88, 95 percent CI, 0.86–0.90, respectively). These associations were more pronounced with a longer follow-up duration.

“In the older cohort, not only were men born SGA more likely to have received a diagnosis of infertility than men born average for gestational age (AGA), but they were in addition more likely to have needed donated spermatozoa to become fathers,” the authors noted. “In assisted reproductive technology (ART) treatments [using] the man’s own sperm cells, men born SGA were more likely to have used intracytoplasmic sperm injection than men born AGA.”

Such findings, according to the authors, suggest that men born SGA might be at increased risk of male factor infertility, including azoospermia. Additionally, it is possible that the group of men born preterm, SGA, or with LBW did not try to conceive as often as did the group of those with normal birth characteristics, given that the success rate of ART and the mean age at birth of the first child did not differ between them, and that more men with less favourable birth characteristics were single (9 percent vs 7 percent).

“Infertility can only be diagnosed (and treated) if a man has tried to conceive and is therefore more common among fathers than among nonfathers,” the authors pointed out.

They also acknowledged that evaluating environmental factors, which potentially affect fertility via testicular dysgenesis syndrome and the intrauterine environment, would have been ideal. “In a future study, such environmental data, with changes over time and between different geographic regions, should shed more light on the mechanisms behind the influence of birth characteristics on reproductive potential.”