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Monitoring uterine contractions with an internal uterine pressure catheter (internal tocodynamometry) during induced labour should not be done on a routine basis, a view that to some extent contradicts existing some professional society recommendations, according to new research published in the January 28, 2010 issue of the New England Journal of Medicine.

"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," write Jannet J. H. Bakker, MSc, Academic Medical Center, Amsterdam, the Netherlands, and colleagues. "However, few data are available to test this hypothesis."

The American College of Obstetricians and Gynecologists (ACOG) and the Society of Obstetricians and Gynaecologists of Canada (SOGC) recommend the use of internal tocodynamometry in obese mothers, where there is no one-on-one nursing/midwifery available, or when response to oxytocin is limited. The Dutch Society of Obstetrics and Gynaecology recommends its use in all cases of induction or augmentation of labour, the study authors note.

The goal of this study was to compare the effect of internal tocodynamometry vs external monitoring on the rate of operative delivery, including caesarean deliveries and instrumented vaginal deliveries in women who required induced or augmented labour. It also assessed complications from use of the intrauterine pressure catheter, the use of antibiotics during labour, time from randomisation to delivery, and adverse neonatal outcomes with the 2 monitoring methods.

The study population included almost 1500 women with a singleton pregnancy with a gestational age of more than 36 weeks, a fetus with the head being the leading part (cephalic presentation), and an indication for induction or augmentation of labour with intravenous oxytocin.

A total of 734 women were randomly assigned to receive internal tocodynamometry, and 722 women received external monitoring.

Type of monitoring and operative delivery

The investigators found that both monitoring methods were associated with similar rates of caesarean deliveries and instrumented vaginal deliveries. Of those who received internal tocodynamometry, almost a third (31.3%) required operative delivery which was statistically similar to those assigned to external monitoring with whom the figure was  29.6%. (relative risk with internal monitoring, 1.1; 95% confidence interval [CI], 0.91 - 1.2; P = .50).

Antibiotic use and internal monitoring

The frequencies of antibiotic use and the time from randomisation to delivery were similar in both groups. The rate of adverse neonatal outcomes was 14.3% with internal monitoring and 15.0% with external monitoring. There were no reported complications with use of the intrauterine pressure catheter, and no neonatal or maternal deaths occurred in either group, the authors report.

Evidence of benefit

Although ACOG and SOGC recommend internal tocodynamometry during induction of labour in obese women, a post hoc subgroup analysis of obese women in this study showed no evidence of benefit, the authors point out.

Noting the limitations of their study, the authors point out that 12% of the women assigned to external monitoring received internal monitoring at the discretion of their physician. However, when the data were analysed according to the actual treatment provided, results were similar to those of the intent-to-treat analysis. Also, the study was not blinded, but it is "unlikely" that knowing the type of monitoring biased decisions about the method of delivery, they write.

Potential risks of internal monitoring

The authors comment that internal tocodynamometry is associated with serious risks, including placental or fetal vessel damage, infection, and anaphylactic reaction.

Although none of these events were observed in this study, it was not powered to detect them, they add.

The results of the trial "do not support the routine use of internal tocodynamometry for monitoring contractions in women with induced or augmented labour," the study authors conclude.

Internal womb contractions monitoring not for routine use