In term babies, steroids from the fetal zone of the adrenal gland decl
ine in the blood and urine in the first few weeks after birth. In infa
nts born prematurely, fetal zone steroids (3 beta-OH-5ene steroids) pe
rsist but it is not known for how long. The present study set out to a
ddress this by examining changes in the synthesis and metabolism of ad
renal steroids with postconceptional age, using serial measurements of
steroid metabolites in the urine. 27 preterm infants, median gestatio
n 29 weeks (range 24-31 weeks) and median birth weight 933g were exami
ned. 3 beta-OH-5ene steroids represented around 90% of the total stero
ids 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 mu g kg(-1) d(-1), until 3-4 weeks past term, after which t
hese urinary fetal zone steroid metabolites declined, falling to 500 m
u g 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 feta
l zone activity rather than birth.