Saliva estriol measurements: an alternative to the assay of serum unconjugated estriol in assessing feto-placental function.

We have investigated the possibility of replacing measurements of maternal serum estriol (E3) with maternal saliva E3. Saliva and serum E3 concentrations were measured by RIA in samples obtained from normal subjects in late pregnancy. The saliva E3 was found to accurately reflect the serum unbound unconjugated E3 and was directly proportional to total serum unconjugated E3. The variability in saliva E3, as assessed by the coefficient of variation for samples collected at intervals of 1 day, 1 h, or 10 min (16.5%, 22.7%, and 13.1% respectively) was not significantly different from published data on the variability in serum E3. No diurnal variation was apparent in samples collected every hour throughout the waking period of a normal day (n = 23). The increase in saliva E3 with gestational age was consistent with the well established pattern for serum E3, with the median value exhibiting a small but significant rise between 32 and 33 weeks and a larger rise between 36 and 37 weeks. The ease with which saliva samples may be collected procedure together with the high correlation between saliva and serum unconjugated E3 levels suggest that assay of saliva E3 should replace serum E3 measurement for assessing feto-placental wellbeing.