A monthly cycle in the adrenocortical function during third trimester pregnancy.

Eleven healthy women were examined three times a week during the third trimester. The possibility of monthly cyclical changes in the serum concentrations of cortisol, placental hCG and fetoplacental estradiol was tested because of previous findings of highly significant monthly cycles in aldosterone and progesterone. A semiparametric statistical model was used and a highly significant monthly cycle in serum cortisol was found, whereas the amplitude for a cycle in hCG was barely significant and non-significant for estradiol. The previous findings of monthly cycles in aldosterone and progesterone, using a parametric multivariate model, were retested by the semiparametric method employed for the present publication. The findings of highly significant cycles in aldosterone and progesterone were corroborated. We think that the results indicate the existence of an adrenocortical cycle. We think that the monthly ovarian cycle in the non-pregnant state is paralleled by an adrenocortical cycle, where changes in aldosterone are "linked" with changes in progesterone and changes in cortisol with changes in estrogens. During pregnancy the adrenocortical cycle persists, probably controlled by the maternal hypothalamus. The physiological background for this monthly endocrine cycle during pregnancy is enigmatic.