Low Birth Weight Associated With Increased Risk for Infertility in Men

Premature baby boy
Premature baby boy in incubator and mom carrying him while he sleeps
Boys born small for gestational age are at a higher risk for infertility in adulthood.

Boys born small for gestational age (SGA) are at a higher risk for infertility in adulthood compared with boys born appropriate for gestational age (AGA), according to study results published in Human Reproduction. There was no association between SGA and infertility in women.

Previous studies have suggested that fetal growth restriction and low birth weight may be associated with reproductive problems in adulthood. The goal of the current study was to explore the association between birth weight for gestational age and infertility in men and women.

The population-based study was based on data from a Danish birth cohort, with information on birth gestational age and birth weight obtained from the birth records of individuals born between 1984 and 1987. The cohort was followed until the end of 2017. A birth weight below the 10th percentile was classified as SGA, while AGA was defined as birth weight between the 10th and 90th percentile. Infertility was defined as having received a diagnosis of infertility and/or fertility treatment.

The cohort included 10,936 patients (mean age at end of follow-up, 32 years), including 5342 women and 5594 men. Of these, 553 women (10.4%) and 586 men (10.5%) were born SGA.

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Infertility was recorded in 533 women (10%) and 332 men (5.9%). The researchers found that 8.3% of the men born SGA were diagnosed or were being treated for infertility compared with 5.7% of men born AGA.

While there was no association between SGA and infertility in women, there was a 55% increased risk for infertility in men born SGA (adjusted odds ratio, 1.55; 95% CI, 1.09-2.21) compared with men born AGA. After exclusion of men with hypospadias or cryptorchidism, the risk for infertility was somewhat attenuated (adjusted odds ratio, 1.37; 95% CI, 0.93-2.01).

The researchers noted several study limitations, including the use of different methods to estimate gestational age, which may have caused misclassification. In addition, the definition of infertility included any record of fertility treatment, which may be used for reasons other than inability to achieve pregnancy, such as in cases of sexual dysfunction or same-sex couples.

“Many children are born SGA, so if SGA is causally linked to infertility, this has public health relevance. It is therefore important to focus on the underlying mechanisms that can explain the possible association between SGA and infertility as it allows a more targeted prevention strategy,” concluded the researchers.

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Thorsted A, Lauridsen J, Høyer B, et al. Birth weight for gestational age and the risk of infertility: a Danish cohort study [published online December 13, 2019]. Hum Reprod. doi:10.1093/humrep/dez232