Birth weight for gestational age and the risk of infertility: a Danish cohort study

Abstract STUDY QUESTION Is birth weight for gestational age associated with infertility in adulthood among men and women? SUMMARY ANSWER Being born small for gestational age (SGA) was associated with infertility in adulthood among men. WHAT IS KNOWN ALREADY Fetal growth restriction may affect fertility, but results from previous studies have been inconsistent. STUDY DESIGN, SIZE, DURATION In this population-based cohort study, we used data from a Danish birth cohort, including 5594 men and 5342 women born between 1984 and 1987. Information on infertility was obtained from Danish health registers during the period from the participants’ 18th birthday and up until 31 December 2017. PARTICIPANTS/MATERIALS, SETTING, METHODS Participants were men and women born in two Danish municipalities, Aalborg and Odense. Information on birth weight and gestational age was obtained from birth records, and information on infertility diagnoses and fertility treatment was retrieved from the Danish National Patient Registry (NPR) and the Danish In Vitro Fertilisation (IVF) registry. Information on potential maternal confounders was obtained from questionnaires during pregnancy and was included in adjusted analyses. Logistic regression analysis was used to estimate crude and adjusted odds ratios (ORs) with 95% confidence intervals (CIs) for infertility according to birth weight for gestational age. MAIN RESULTS AND THE ROLE OF CHANCE Men born SGA had a 55% higher risk of being diagnosed with or treated for infertility compared to men born appropriate for gestational age (AGA) (adjusted OR = 1.55, 95% CI: 1.09–2.21). The association attenuated after exclusion of men born with hypospadias or cryptorchidism (OR = 1.37, 95% CI: 0.93–2.01). No association was found between women’s birth weight for gestational age and risk of infertility (adjusted OR = 1.00, 95% CI: 0.73–1.37). LIMITATIONS, REASONS FOR CAUTION Estimation of gestational age is associated with some uncertainty and might have caused non-differential misclassification. The study design implicitly assumed similar distribution of reproductive and health-seeking behaviour across the groups that were compared. WIDER IMPLICATIONS OF THE FINDINGS Men born SGA had a higher risk of infertility. Genital malformations may account for part of the observed association, but this must be explored further. STUDY FUNDING/COMPETING INTEREST(S) This study was supported by Health, Aarhus University. No competing interests are declared. TRI