Abstract
Saliva specimens were collected at weekly intervals during the third trimester of 61 uncomplicated pregnancies. Oestriol concentrations, measured in samples collected in the early morning from fasting, recumbent subjects, were used to construct a provisional normal range. This proved to be higher than the corresponding normal range reported from another laboratory applying the same method to samples obtained at random from a different population of ambulant subjects. Interlaboratory variation in the assay of salivary oestriol was not sufficient to account for the difference in normal range. It is concluded that consideration should be given to the timing of sample collection if salivary oestriol concentration is to be monitored as a possible means of assessing fetoplacental function. A normal range for salivary oestriol concentration versus gestational age obtained from women sampled randomly may not be appropriate for monitoring patients with ‘at-risk’ pregnancies who are normally bed-rested.