No previous studies could be located regarding a link between an elevation in urobilinogen and/or minor maternal weight loss and parturition, labor, onset. There have been studies to suggest rationale for our clinical observation, however. Estrogens and progesterone both play a role in the growth and contractility of uterine myometrial cells. Progesterone tends to promote uterine relaxation, hence the name "pro-gest…". In most species, progesterone levels dramatically fall, a 'withdrawal', prior to the onset of labor. However, in human and higher level primates, the progesterone and estrogen levels are both elevated in later gestation and during parturition. The "withdrawal" in humans, therefore, may be mediated by changes in the myometrial responsiveness to progesterone (2).