What Electronic Fetal Monitoring entails:
External: two belts around the mother's abdomen. one is an ultrasound device that monitors the baby's heartbeat, the other monitors the intensity of the contractions.
Internal: a spiral wire electrode is placed in the skin of the baby's scalp to detect fetal heart rate and a a fluid filled tube is placed in the mom's uterus to measure intensity of contractions. It requires the amniotic sac to be broken (which increases chance of infection).
Outcomes after Internal versus External Tocodynamometry for Monitoring Labor
Background It has been hypothesized that internal tocodynamometry, as compared with external monitoring, may provide a more accurate assessment of contractions and thus improve the ability to adjust the dose of oxytocin effectively, resulting in fewer operative deliveries and less fetal distress. However, few data are available to test this hypothesis.
Methods We performed a randomized, controlled trial in six hospitals in the Netherlands to compare internal tocodynamometry with external monitoring of uterine activity in women for whom induced or augmented labor was required. The primary outcome was the rate of operative deliveries, including both cesarean sections and instrumented vaginal deliveries. Secondary outcomes included the use of antibiotics during labor, time from randomization to delivery, and adverse neonatal outcomes (defined as any of the following: an Apgar score at 5 minutes of less than 7, umbilical-artery pH of less than 7.05, and neonatal hospital stay of longer than 48 hours).
Results We randomly assigned 1456 women to either internal tocodynamometry (734) or external monitoring (722). The operative-delivery rate was 31.3% in the internal-tocodynamometry group and 29.6% in the external-monitoring group (relative risk with internal monitoring, 1.1; 95% confidence interval [CI], 0.91 to 1.2). Secondary outcomes did not differ significantly between the two groups. The rate of adverse neonatal outcomes was 14.3% with internal monitoring and 15.0% with external monitoring (relative risk, 0.95; 95% CI, 0.74 to 1.2). No serious adverse events associated with use of the intrauterine pressure catheter were reported.
Conclusions Internal tocodynamometry during induced or augmented labor, as compared with external monitoring, did not significantly reduce the rate of operative deliveries or of adverse neonatal outcomes. (Current Controlled Trials number, ISRCTN13667534 [controlled-trials.com] ; Netherlands Trial number, NTR285.)
Basically what it means is that they thought that internal fetal monitoring with an intrauterine pressure catheter would be better than external fetal monitoring at catching fetal distress and saving the day in women who had induced or augmented labor, but what they found was the data for the two was pretty close.
The researchers found that the operative delivery rate wasn't significantly different between the internal or external groups (31.3 versus 29.6 percent). Adverse neonatal outcomes, including Apgar score of less than seven at five minutes or neonatal hospital stay of longer than 48 hours, weren't significantly different between the groups, either (14.3 versus 15 percent).
"Internal tocodynamometry has serious risks, including placental or fetal-vessel damage, infection, and anaphylactic reaction. We did not observe any complications of internal monitoring in our study, but it was not powered to detect these events, which in previous studies had an estimated incidence of one in 300 patients and one in 1400," the authors conclude. "The results of our trial do not support the routine use of internal tocodynamometry for monitoring contractions in women with induced or augmented labor."
For the science-minded ones, here is part of Data charts from the study results (click to enlarge):