Establishment of hormone reference intervals for infants born < 30 weeks' gestation

Objective: Preterm infants, especially those born very preterm (<32 weeks' gestation), suffer a number of morbidities. Immaturity of the endocrine system and its potential impact on morbidity is the subject of numerous studies. Hormone concentrations are sometimes measured in very preterm infants, however there are little normative data available to be able to interpret the results. The aim of this study was to describe age appropriate hormone reference intervals for babies born less than 30 weeks' gestation.

Study design: Samples were collected at 1, 4, 7, 14, 21, 28 and 42 days after birth from babies born 23-29 weeks' gestation. The serum was analyzed for seven hormones by automated chemiluminescent immunoassay (Siemens Immulite 2000). Results from the 107 infants who survived beyond 40 weeks' corrected gestational age were included in the data analysis.

Results: Cortisol, dehydroepiandrosterone sulfate, growth hormone and progesterone levels were highest during the first seven days with levels up to 10,801nmol/L; 26.6μmol/L; 343mU/L; and >63.6nmol/L respectively. Free thyroxine levels were as low as <2.6pmol/L for the first 28 days with the nadir at 7days. Estradiol levels ranged from <73 to 1626pmol/L over the six weeks. Reference intervals for IGF-1 could not be established as the levels were below the analyzer's sensitivity. There were no differences in reference intervals between male and female infants.

Conclusions: We describe gestation appropriate reference intervals for six hormones measured in babies born <30 weeks' gestation. Utilization of these reference intervals permits the correct and timely interpretation of results to the clinician.