Table 6 Summary of the occurrence of uterine contractions in relation to plasma levels of oxytocin during labour without and with synthetic oxytocin

Dissociation between oxytocin levels and uterine contractions

The time relationship between oxytocin levels and uterine contractions was studied in 4 of the articles. In all of these studies, no association was found between oxytocin peaks and uterine contractions: Gibbens 1976 [16], Dawood 1979 [18], Leake 1981 [19], Otsuki 1983 [20].

Effect of synthetic oxytocin administration on oxytocin levels and uterine contractions

Infusions of synthetic oxytocin at a rate of 4–6 mU/minute gave rise to a significant rise in oxytocin levels in women at term without labour, which corresponded to the oxytocin levels seen during physiological labour. At an infusion rate of 10–16 mU/min, oxytocin levels were higher than physiological levels (Fuchs 1983 [23]). Doubling the dose lead to doubled levels (Fuchs 1983 [23]), Amico 1984 [24]), Bolus injections of 4–8 mU of synthetic oxytocin in women at term, without labour gave rise to an increase of oxytocin levels of the same size as observed during physiological oxytocin pulses and was associated with uterine contractions. (Fuchs 1991 [31]).