FETAL OXYTOCIN AND ITS EXTENDED FORMS AT TERM WITH AND WITHOUT LABOR

OBJECTIVE: We examined the concentrations of oxytocin and extended for ms df oxytocin in umbilical plasma with and without labor. STUDY DESIG N: Umbilical venous and arterial blood were sampled in 27 term fetuses delivered vaginally and 13 delivered abdominally before labor. Extend ed forms and oxytocin were measured by radioimmunoassay and compared b y analysis of variance or t test. RESULTS: Concentrations of extended forms were higher than oxytocin concentrations (24.7 +/- 3.1 vs 6.1 +/ - 1.2 pg/ml, p < 0.01). Extended forms were higher in umbilical venous than in arterial plasma (29.6 +/- 5.0 vs 19.8 +/- 3.1 pg/ml, p < 0.05 ); oxytocin concentrations were not significantly different (4.7 +/- 1 .6 vs 7.8 +/- 1.8 pg/ml). Concentrations of extended forms were marked ly lower with than without labor (17.1 +/- 3.0 vs 37.1 +/- 5.7 pg/ml, p = 0.01). Ratios of extended forms over oxytocin decreased with labor . CONCLUSION: In umbilical plasma extended forms of oxytocin are more abundant than oxytocin. Extended forms originate in the uterus and dec rease markedly with labor.