Observations on maternal oxytocin release during human labor and the effect of intravenous alcohol administration.

Serial blood samples were obtained from 97 women in spontaneous labor, and oxytocin levels were determined by a sensitive and highly specific radioimmunoassay. The following observations were made: (1) The hormone is released in a series of "spurts"; (2) the peak levels achieved are usually 2 to 5 muU per milliliter and never exceed 12.5 muU per milliliter; (3) the frequency of spurt release increases as labor progresses, reaching a maximum in the second stage; (4) the frequency of spurt release is reduced during intravenous infusion of alcohol at levels which produce no obvious effect on uterine activity.