Internal Versus External Tocodynamometry: Which Has Better Outcomes?

Monitoring uterine contractions with internal tocodynamometry (IT) versus external tocodynamometry (ET) results in similar maternal and neonatal outcomes in women whose labor is induced or augmented with oxytocin, according to an intervention review and meta-analysis conducted by the Cochrane Pregnancy and Childbirth Group.¹
   
It is especially important to monitor uterine contractions when oxytocin is used because uterine hyperstimulation or tachysystole can lead to fetal distress. Whereas ET measures contractions through an external device held in place by a belt, IT involves the placement of an intrauterine pressure catheter inside the uterus next to the baby. It is generally painless but is only possible after the rupture of the membranes. According to the researchers, contractions are measured more accurately with IT, which could result in near-ideal dosing of oxytocin. However, IT is associated with higher costs than ET and with a risk of placental or fetal vessel damage-a rare but serious complication.
   
To better understand the effectiveness of IT compared with ET when intravenous oxytocin is used to induce or augment labor, researchers reviewed relevant randomized controlled trials. A total of 3 studies of moderate quality were selected and provided data on 1945 women. There were no reports of maternal or neonatal death in any of the studies. Neonatal outcomes (Apgar score of less than 7 at 5 minutes, an umbilical artery pH of less than 7.15 and of less than 7.16, admission to the neonatal intensive care unit, and more than 48 hours of hospitalization) did not differ significantly between study groups. In addition, there were no significant differences between study groups in the number of instrumental deliveries or cesarean sections, the use of analgesia, and time to delivery. Also, women in whom an intrauterine catheter was placed had no increased risk of infection.
   
Currently, the American College of Obstetricians and Gynecologists does not recommend the routine use of intrauterine pressure catheters for monitoring contractions but does support that these devices may have some benefit in obese women, when there is a lack of one-on-one nursing care, and when the patient’s response to oxytocin is limited.² In light of the current findings, the researchers have concluded that there is insufficient evidence to recommend one form of tocodynamometry over another.

Pertinent Points:
- Both forms of tocodynamometry-external and internal-result in similar maternal and neonatal outcomes.
- Internal tocodynamometry was not associated with an increased risk of infection.
- Although internal tocodynamometry measures uterine contractions more accurately, there is an associated risk of a rare but serious complication of placental or fetal vessel damage.
 

References:

1. Bakker JJ, Janssen PF, van Halem K, et al. Internal versus external tocodynamometry during induced or augmented labour. Cochrane Database Syst Rev. 2012;12:CD006947. doi: 10.1002/14651858.CD006947.pub2.
2. American College of Obstetrics and Gynecology Committee on Practice Bulletins-Obstetrics. ACOG practice bulletin number 49, December 2003: dystocia and augmentation of labor. Obstet Gynecol. 2003;102:1445-1454.