The normal increase in adrenal secretion during pregnancy contributes to maternal volume expansion and fetal homeostasis.

OBJECTIVE: This study was designed to test the hypothesis that the increase in maternal cortisol and aldosterone in pregnancy is critical to maternal and fetal homeostasis.
METHODS: Pregnant ewes were adrenalectomized (at approximately 112 days), and aldosterone and cortisol were given to either normal pregnant level (1 mg/kg per day cortisol and 3 microg/kg per day aldosterone) or nonpregnant level (half the dose of either cortisol or aldosterone). Blood samples for measurement of fetal and maternal plasma electrolytes, cortisol, and adrenocorticotropic hormone (ACTH) were collected at days 120, 125, and 130; fetal and maternal blood pressure and heart rate and maternal plasma volume were measured at days 120 and 130.
RESULTS: Reduction of maternal cortisol or aldosterone decreased maternal plasma volume at 130 days. In the fetuses in the low cortisol group, cortisol concentrations were lower and ACTH concentrations were higher; however, there was no increase in fetal cortisol with age in the low cortisol or low aldosterone groups. Fetal arterial pressure was decreased in all groups of adrenalectomized ewes at 120 days and decreased in the low cortisol group at 130 days. Fetal arterial pressure was significantly related to maternal plasma volume at 130 days. Fetal arterial oxygen tension at 120 days was decreased in fetuses of low aldosterone ewes and was correlated with plasma volume. Overall fetal arterial oxygen tension correlated with fetal cortisol. Fetal ACTH concentrations correlated positively with fetal cortisol but negatively with fetal blood pressure.
CONCLUSION: Maternal adrenal secretion maintains the normal increase in maternal plasma volume and fetal cortisol and indirectly supports fetal arterial oxygen tension, blood pressure, and adrenal secretion.