Longitudinal profiles of relaxin and progestagens during pregnancy, pregnancy loss and false pregnancy in the killer whale (Orcinus orca)

•Relaxin profiles during pregnancy in killer whales were described.•Relaxin increases 800% increase during the week prior to parturition.•Relaxin concentrations may be used to confirm later term pregnancy.•The corpus luteum appears to be the major source of relaxin throughout pregnancy.•Low progesterone during early pregnancy may foreshadow future pregnancy loss. The circulating pattern of immunoreactive relaxin and progestagens based on monthly and gestational stage (early, mid, late) profiles were determined during pregnancies that resulted in live calves (LIVE, n = 30), stillbirths (STILLB, n = 3), abortions (ABORT, n = 5) and presumptive false pregnancies (FALSE, n = 8), and during the follicular (n = 34) and luteal phase (n = 58). Monthly LIVE relaxin concentrations steadily increased during gestation, but values did not significantly exceed those of the luteal phase until 9 months prior to parturition, peaking during the final month at 2356 ng/ml. Relaxin surged (P