Monitoring uterine activity during labor: a comparison of 3 methods

Abstract

Objective: Tocodynamometry (Toco; strain gauge technology) provides contraction frequency and approximate duration of labor contractions but suffers frequent signal dropout, necessitating repositioning by a nurse, and may fail in obese patients. The alternative invasive intrauterine pressure catheter (IUPC) is more reliable and adds contraction pressure information but requires ruptured membranes and introduces small risks of infection and abruption. Electrohysterography (EHG) reports the electrical activity of the uterus through electrodes placed on the maternal abdomen. This study compared all 3 methods of contraction detection simultaneously in laboring women.

Study design: Upon consent, laboring women were monitored simultaneously with Toco, EHG, and IUPC. Contraction curves were generated in real-time for the EHG, and all 3 curves were stored electronically. A contraction detection algorithm was used to compare frequency and timing between methods. Seventy-three subjects were enrolled in the study; 14 were excluded due to hardware failure of 1 or more of the devices (n = 12) or inadequate data collection duration (n = 2).

Results: In comparison with the gold-standard IUPC, EHG performed significantly better than Toco with regard to the Contractions Consistency Index (CCI). The mean CCI for EHG was 0.88 ± 0.17 compared with 0.69 ± 0.27 for Toco (P < .0001). In contrast to Toco, EHG was not significantly affected by obesity.

Conclusion: Toco does not correlate well with the gold-standard IUPC and fails more frequently in obese patients. EHG provides a reliable noninvasive alternative, regardless of body habitus.

Figure 1

Electrode location. Abbreviations: DRL (Driven Right Leg); CMS (Common Mode Signal)

Figure 2

Plot of consistent contractions per patient for both methodologies EHG vs. IUPC and Toco vs. IUPC. Each dot corresponds to one subject. Those near the diagonal indicate the non-invasive method is equivalent to IUPC; those below the diagonal indicate superiority of IUPC.

Figure 3

Plot of sensitivity versus BMI. Open dots and dashed line (best linear fit) represent EHG observations; filled dots and solid line represent Toco observations. As BMI increases, sensitivity decreases for both technologies, however the relationship is steeper for Toco.