Activity of the adrenal fetal zone in preterm infants continues to term

In term babies, steroids from the fetal zone of the adrenal gland decline in the blood and urine in the first few weeks after birth. In infants born prematurely, fetal zone steroids (3 beta-OH-5ene steroids) persist but it is not known for how long. The present study set out to address this by examining changes in the synthesis and metabolism of adrenal steroids with postconceptional age, using serial measurements of steroid metabolites in the urine. 21 preterm infants, median gestation 29 weeks (range 24-31 weeks) and median birth weight 933g were examined. 3 beta-OH-5ene steroids represented around 90% of the total steroids excreted until 2 weeks past term, falling to 55% by 12 weeks after term. 3 beta-OH-5ene steroids were excreted in the urine at levels of 1500-2000 micrograms kg-1 d-1, until 3-4 weeks past term, after which these urinary fetal zone steroid metabolites declined, falling to 500 micrograms kg-1 d-1 six weeks past term. We conclude that activity of the adrenal fetal zone in preterm infants continues to term, after which it diminishes. This suggests that it is gestation that determines fetal zone activity rather than birth.