According to a study published in the New England Journal of Medicine, internal tocodynamometry—the use of an intrauterine pressure catheter during induced or augmented labor—did not improve outcomes for either the mother or her baby when compared with external monitoring.
Researchers in the Netherlands randomized 1456 women who required induction or augmentation of labor at six different hospitals to either internal tocodynamometry (n=734) with a sensor-tipped intrauterine catheter system or monitoring with an external tocodynamometer (n=722). The attending obstetricians were not blinded to the randomization. Crossover to internal monitoring was allowed if women had no cervical progression for 2 hours, if uterine contractions were insufficient, or if doctors were considering cesarean section.
The primary outcome—cesarean section or instrumented vaginal delivery—did not differ between the groups (31.9 % versus 29.6; P=0.50). Women were no less likely to have cesarean or instrumented vaginal delivery with internal monitoring (relative risk [RR], 1.1 versus external monitoring; 95% confidence interval [CI], 0.91 to 1.2). In addition, there were no significant differences in secondary outcomes such as maternal use of antibiotics, neonatal admission, use of analgesia, or time from randomization to delivery. The authors calculated that, based on the confidence intervals obtained, internal tocodynamometry would result in anywhere from a 17% risk reduction to a 30% increase in cesarean section.
Although internal tocodynamometry has documented risks, there were no reported complications associated with the monitoring and no deaths occurred in either group. However, the study was not powered to detect some risks that have been noted in prior studies such as placental or fetal-vessel damage, infection, and anaphylactic reaction. Notably, women with a high body mass index—a subgroup specifically recommended for internal uterine activity monitoring by various professional medical organizations—showed no benefit. The results should be interpreted with caution since the study was an ad hoc analysis and of limited power.
Professional recommendations regarding internal tocodynamometry have been based primarily on expert opinion and without the benefit of robust clinical data. While this study has several limitations—such as its unblinded design and lack of power to determine several specific outcomes and associations—it offers new clinical insight that might influence the current recommendations.