Introduction

The interpretation of intrapartum electronic fetal monitoring and use of this information to improve neonatal outcomes has been a challenge for obstetricians. Recently, attention has turned to the effect of uterine activity on intrapartum fetal heart rate (FHR) and maternal and neonatal outcomes. In 2008, a formalized definition of excessive uterine activity, or tachysystole, and recommendations for management of this clinical finding were established at a workshop sponsored by 3 national groups. Specifically, tachysystole is characterized as more than 5 contractions in 10 minutes, averaged over a period of 30 minutes. This month, Journal Club members discussed a new in-depth study of this phenomenon.

Heather Frey, MD, and George A. Macones, MD, MSCE, Associate Editor

Introduction

The interpretation of intrapartum electronic fetal monitoring and use of this information to improve neonatal outcomes has been a challenge for obstetricians. Recently, attention has turned to the effect of uterine activity on intrapartum fetal heart rate (FHR) and maternal and neonatal outcomes. In 2008, a formalized definition of excessive uterine activity, or tachysystole, and recommendations for management of this clinical finding were established at a workshop sponsored by 3 national groups. Specifically, tachysystole is characterized as more than 5 contractions in 10 minutes, averaged over a period of 30 minutes. This month, Journal Club members discussed a new in-depth study of this phenomenon.

Heather Frey, MD, and George A. Macones, MD, MSCE, Associate Editor

Study Design

Frey: What was the aim of this study?

Meister: This retrospective cohort study investigated tachysystole in the context of the recently clarified definition by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the American College of Obstetricians and Gynecologists, and the Society for Maternal-Fetal Medicine. The authors were particularly interested in defining the overall incidence of tachysystole, identifying particular risk factors, describing associated FHR changes, and assessing both maternal and neonatal outcomes.

Frey: Do you think studies evaluating tachysystole are relevant to clinical practice? How?

Kleweis: Definitely. We use tocometry to monitor the contractile force being exerted during labor for progression of cervical dilation and delivery. As obstetricians, we use this information to guide management and employ interventions, such as augmentation or induction, to manipulate uterine force. Specifically, increased information about the effect of contractions on fetal and maternal outcomes is relevant and most likely to influence clinical practice.

Frey: Let’s discuss the evaluation of various tachysystole events (TS, TS-F, TS-I, TS-D). What is your opinion of this approach?

Meister: The authors subcategorized tachysystolic events into events occurring alone (TS), occurring with associated FHR changes (TS-F), prompting intervention (TS-I), and prompting expedited delivery (TS-D). They then identified risk factors for tachysystole in the context of these predetermined categories. It is helpful to break down the analysis in this way to delineate clinically significant tachysystole resulting in FHR changes, intervention, or expedited delivery from isolated tachysystole. The risk factors that contribute to clinically significant TS may differ from those associated with isolated TS. The approach to management of these risk factors may differ as well, especially if the maternal and fetal outcomes vary by the category of tachysystole.

Frey: The authors evaluated multiple neonatal outcomes, including a composite outcome. What do you think of the outcomes evaluated? Are there other outcomes that you would have included?

Kleweis: Some of the fetal outcomes the authors measured seemed less likely to result from uterine tachysystole than others based on the proposed mechanism by which uterine activity triggers adverse outcomes—decreased placental and fetal perfusion leading to acidemia. In addition, outcomes such as necrotizing enterocolitis, respiratory complications, and intraventricular hemorrhage are commonly related to preterm birth. Thus, it is not surprising that in this term cohort the occurrence of these events are rare, and their absolute risk is low. A more accurate measurement of the impact of tachysystole on fetal well-being would have been umbilical cord gases. These data were unavailable for analysis, and the authors acknowledge this as a limitation of their study.

In the analysis, a composite neonatal outcome, defined as low Apgar score, sepsis, intraventricular hemorrhage, necrotizing enterocolitis, or pneumothorax, was also evaluated and found to be statistically more common among cases of tachysystole. However, when I looked further at the rates of each individual component in relationship to presence of tachysystole, it appears that the difference in the composite outcome is related to differences in rates of sepsis and not the other outcomes. This highlights one of the disadvantages of using a composite outcome because important individual associations can be lost when the outcome data is combined. In this case, the authors presented individual association results for each of the composite components, which provide all the information necessary for readers to draw the correct conclusions.

Lastly, the outcomes significantly associated with tachysystole, such as neonatal intensive care unit admission and sepsis, could have been influenced by confounding factors, such as maternal characteristics or length of labor. This is something that future studies evaluating the effects of tachysystole should explore.

Frey: In general, what is the statistical analysis approach of generalized estimating equations (GEE)? When is it used?

Stuart: GEE is a multivariate approach that can be used to analyze correlated or longitudinal data. It is a weighted approach that uses clusters, in this case a single woman with multiple tachysystole events within the period of interest. The advantage of GEE is that it produces reasonably accurate confidence intervals by estimating a weighted sample size.