ESPE Abstracts

Background: Hypothalamic–pituitary–gonadal (HPG) axis activates soon after birth, and this ‘minipuberty’ provides a transient phase for evaluation of the function of the HPG axis in early infancy. Substantial differences in postnatal gonadotropin secretion have been reported between preterm (PT) and full-term (FT) boys and girls. Therefore, when evaluating gonadotropin levels in infants, time from birth (calendar age), maturity (postmenstrual, PM age) and sex should be considered.

Objective and Hypotheses: We constructed sex-specific reference intervals for urinary gonadotropin levels in FT and PT infants according to calendar and postmenstrual age.

Method: LH and FSH levels were measured in spot urinary samples with time-resolved immunofluorometric assay (AutoDELFIA, Perkin Elmer, Wallac, Turku, Finland) and corrected for urinary creatinine. Altogether 989 urinary samples of 193 infants (101 boys) born at 23.4–42.1 gestation weeks were analyzed. Samples were collected from 1.0 week–6.5 months of age.

Results: Infants were divided in three groups according to gestational age at birth: <32, 32–36, and ≥37 weeks. Reference intervals for LH and FSH levels in urine were constructed for 1 week to 2 months of age, 2–4 months of age and >4 months of age. PM age was strongly associated with both LH and FSH levels in PT infants, and from approximately 40 weeks of PM age, the levels of PT infants were in the same range as in FT infants.

Conclusion: These data provide reference intervals for urinary gonadotropins during the first 6 months of life in infants born as early as at 24th gestational week. These normative values help to better understand the notable changes in gonadotropin levels during the first months of life in PT and FT infants.