Context: Newborn infants show a postnatal decline in androgen levels as the fetal adrenal glands involutes.

Hypothesis: Placental factors up-regulate DHEA-S generation. Hence, regardless of age, parturition will result in fetal adrenal involution and decline in DHEA-S levels.

Subjects and Methods: Premature neonates (n = 30), with gestational age 26-35 wks. Adrenal volume by ultrasonography, and serum DHEA-S, cortisol and androstendione levels were followed weekly between days 1-28 of life.

Results: Serum DHEA-S was high on day 1 of life, declining rapidly regardless of gestational age during the first week of life (P < 0.001) and serum androstendione and cortisol levels followed a similar pattern. Androstendione levels showed a rise as of day 21 of life in boys but not in girls. The adrenals decreased in ultrasonographic volume from day 1 to 14 of life (P < 0.001), regardless of gestational age.

Conclusions: Involution of the adrenal is faster than previously reported, and regardless of gestational age, occurs within the first week of life in terms of hormone secretion and within two weeks in adrenal size. Involution involves a decline in DHEA-S but also in androstendione and cortisol secretion, with a change in enzymatic activity. Males and females differ in their androstendione levels and enzymatic activity. Parturition itself is the basis for fetal adrenal involution, supporting a key role for placental factors in maintaining the fetal adrenal and generating adrenal androgens.