Comparison of uterine activity induced by nipple stimulation and oxytocin

Intermittent nipple stimulation has been proposed as a substitute for exogenous oxytocin infusion in the performance of contraction stress tests. To compare the uterine activity produced by these two methods, we studied a group of 45 term pregnant women undergoing indicated inductions of labor. Twenty-five patients had nipple stimulation and 20 patients received oxytocin infusions according to a study protocol. The two groups were similar in all obstetric parameters. Pre- and posttest uterine activity was measured by internal tocodynamometry and quantified in Montevideo units. A significant increase in uterine activity occurred in both groups (P<.01). Regular uterine activity (three contractions in ten minutes) was achieved more rapidly (P<.005), but at a lower level (P<.001) in the nipple stimulation group. Pre- and posttest tonus did not change significantly in either group. In the nipple stimulation group, five patients (20%) did not achieve adequate contraction patterns after 15 stimulation-rest cycles (a total of 110 minutes) and three subjects (12%) experienced uterine hyperstimulation. These observations suggest that exogenous oxytocin and intermittent nipple stimulation may not have equivalent effects on uterine contractility. Therefore, it may not be justified to substitute one technique for the other or to use the same criteria for interpretation of contraction stress tests produced by both techniques.