Effect of ampicillin administration on estradiol, estriol, and cortisol levels in meternal plasma and on estriol levels in urine.

Ampicillin treatment in the last trimester of pregnancy had no significant effect on the levels of estradiol, estriol, or cortisol in maternal plasma. Urinary estriol excretion was, however, notably decreased during or following ampicillin treatment in six out of 10 patients. These results suggest that the plasma estrogen assays have greater validity than the urinary estriol assay in assessing fetoplacental endocrine function during a period of ampicillin treatment of the mother.