Sub-hourly variations in salivary estriol concentrations in the last trimester of pregnancy

Sub-hourly variations in salivary estriol were measured in women in the last trimester of pregnancy. The mean and variation of salivary estriol concentrations in specimens collected at 5-min intervals for 30 min were greater on awakening in the morning (when subjects were recumbent and fasting) than in the afternoon. The differences in variation between morning and afternoon serial specimens were eliminated by the omission of the first two specimens collected in the morning. Significant differences between the mean concentrations obtained for morning and afternoon specimens were minimized by use of a recumbent posture for the afternoon specimen collection. The mean estriol concentration of four saliva samples collected at 5-min intervals for 15 min did not differ significantly from the concentration of saliva collected continuously over the subsequent 15 min. For routine estriol monitoring, therefore, samples should be collected over a 15-min period. This ought to be carried out at the same time of day, in the same posture on each occasion, but preferably not in the early morning.