Dynamic changes in LH/FSH ratios in infants with normal sex development

Objective: Little is known about the ratio between luteinizing hormone (LH) and follicle-stimulating hormone (FSH) during infancy. This study aimed to evaluate serum and urinary LH/FSH as a marker of sex with age-specific cutoffs in healthy infants. Design: A prospective, longitudinal cohort study of healthy infants aged 0-1.2 years. Methods: In total, 236 healthy infants (122 boys and 114 girls) from The COPENHAGEN Minipuberty Study (ClinicalTrials.gov ID: NCT02784184), with 567 serum and 603 urine samples, were included. Measures of diagnostic accuracy, including sensitivity and specificity, were used to assess the ability of LH/FSH to detect sex in healthy infants. Results: In both serum and urine, LH/FSH was highest in males with minimal overlap between the sexes. In contrast to isolated LH and FSH concentrations, LH/FSH ratios in both serum and urine were excellent markers of sex from 0 to 1.2 years with median sensitivities and specificities ranging from 93 to 100% with correspondingly narrow 95% CIs. Conclusions: Serum and urinary LH/FSH ratios are excellent discriminators of sex in healthy infants during the entire first year of life. The clinical role and application of the ratio remain to be elucidated.

Automated summary

This study evaluated LH/FSH ratios in serum and urine as markers of sex in healthy infants, finding that the ratios were highest in males aged 0-1.2 years with minimal overlap between sexes, serving as excellent discriminators of sex throughout the first year of life. The clinical implications and applications of these ratios require further exploration.