Uterine Tachysystole Rates and Survival of the Fittest Effect

Objective: To determine incidence of uterine tachysystole and its association with decelerations and cesarean birth. Design: Retrospective. Setting: Suburban hospital in a mid-Atlantic city. Sample: Women (6,234) with singleton cephalic presenting infants at a gestational age of 37 weeks or more, who were monitored electronically in the last 4 hours prior to delivery. Methods: Clinical data were obtained from an institutional perinatal database that extracts data from the electronic medical record (PeriBirth, Princeton, NJ). The digital tracings were analyzed using PeriCALM Patterns (Princeton, NJ). We divided each tracing into 10-minute segments that were numbered according to proximity to birth, 0 representing the last 10 minutes before birth and 24 occurring 240 minutes earlier. We counted the number of contractions and decelerations in each time segment Results: In this study, 18.0% of women experienced at least one episode of uterine tachysystole. The incidence of uterine tachysystole was around 2.7% at 4 hours prior to delivery and rose to 8.0% times close to delivery. Continuous uterine tachysystole for more than 120 minutes was very uncommon. Persistent uterine tachysystole was not associated with more decelerations (R =.28) or with higher cesarean rates (R =.23). Only 55% or 0.88% of women in this study met the criteria for labor intolerance. These women had fewer episodes of high contraction rates. In contrast, they showed a much higher deceleration response to contractions especially at very low contraction rates. Overall, the rate of cesarean was positively associated with rising rates of decelerations per contractions (R =.92). Conclusion/Implications for Nursing Practice: We can conclude that some infants tolerate uterine tachysystole well, and some do so for very prolonged periods. These findings are consistent with the principle underlying the contraction stress test (CST), in which a controlled stress via induced contractions was used to determine fetal well-being antepartum. Labor is the ultimate CST, and this analysis showed that infants with the low tolerance to labor demonstrated strong deceleration responses to even small amounts of contraction stress, whereas others tolerated long periods of uterine tachysystole.