Estriol-d3 3-O-Sulfate 16-O-β-D-Glucuronide Sodium Salt is the labeled analogue of Estriol 3-O-Sulfate 16-O-β-D-Glucuronide Sodium Salt (E888985), an analogue of Estriol 16-O-β-D-Glucuronide (E888965), a glucuronide derivative of Estriol (E888960); a metabolite of Estradiol that is considerably less potent than Estradiol itself.