Absence of a Prelabor Relaxin Surge in Women1

Abstract
Serum immunoreactive relaxin concentrations were measured in 74 women sampled within 7 days prior to the onset of spontaneous term labor and again during active spontaneous labor. No significant differences between antepartum and intrapartum values were noted. In contrast to rodents and pigs, no prelabor elevations in relaxin secretion occur in women.