The effect of phenobarbital on serum hormone levels and their diurnal variations in pregnancy.

The effect of phenobarbital (PB) on serum hormones in late pregnancy was investigated. 18 pregnant women were studied before and after 2 weeks of PB treatment (100 mg per os, daily at 8 p.m.) by measuring serum estradiol, estriol, progesterone, testosterone, prolactin and cortisol concentrations. 7 pregnant women without PB therapy served as controls. Estradiol levels in the morning decreased, whereas those of estriol increased both in the morning and evening during PB treatment. The estriol/estradiol ratio increased in women on PB. PB affected the diurnal variation of hormones; the decrease in estradiol concentration between 8 a.m. and 8 p.m. was eliminated and the decrease in estriol concentration became more clear. PB did not significantly affect the serum levels of the other hormones investigated. As an enzyme-inducer PB may affect the fate of sex hormones.