Circadian rhythm and diurnal excursion of plasma cortisol in diabetic pregnant women.

The effect of type I and II diabetes in pregnancy on the circadian rhythm and diurnal excursion of plasma cortisol was studied in the second and third trimesters and post partum. Cosignor analysis demonstrated persistence during gestation of the significant circadian rhythm of the nonpregnant state. As previously reported in control pregnancies, plasma cortisol levels (24-hour mean, nadir, peak, and nadir-peak excursion) increased during gestation while the relative excursion of cortisol (expressed as the percent deviation from the 24-hour mean) was blunted. No significant difference was found between diabetic groups or when diabetic groups were compared with control subjects. Nocturnal hypoglycemia was common among diabetic women during pregnancy and post partum. Although these episodes were usually asymptomatic, the mean concomitant cortisol levels were increased over the corresponding cortisol levels of nonhypoglycemic diabetic and control subjects. We conclude that differences between control and type I and II diabetic subjects in carbohydrate tolerance or glycemic excursion are not explained by differences in cortisol levels or rhythm. The pregnancy-associated blunting of the excursion of cortisol is consistent with an autonomous source of adrenocorticotropin. Asymptomatic nocturnal hypoglycemia is common in insulin-requiring diabetic women and is associated with increased cortisol secretion.