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Association between uterine tachysystole and cord blood lactate in parturients at term gestation
Abstract Number: F5A-3
Abstract Type: Original Research
Uterine tachysystole (UT) occurs in ≈11% of parturients in spontaneous labor and ≈ 30-40% when labor is induced. Despite its ubiquitous occurrence, there is lack of high quality data on its effects on cord blood gases, with studies suggesting either no effect or association with neonatal acidemia. Thus the 2008 NICHD/ACOG recommendations regarding clinical management of tachysystole are based largely on expert opinion. Because UT impairs uteroplacental perfusion and reduces fetal oxygenation, we hypothesized that cord blood lactate could be a sensitive indicator of fetal compromise.
Secondary analysis of a prospective cohort study of all consecutive singleton gestations ≥ 37 weeks admitted for labor to a single tertiary care institution with universal cord gas policy. EFM and contraction patterns in the final hour prior to delivery were extracted by trained obstetric nurses. Patients with UT (‘always’ group), defined according to NICHD criteria, were compared to those without UT (‘never’ group). Primary outcome of interest was cord blood lactate ≥ 4 mmol/L. Secondary outcomes included pH ≤ 7.10, base deficit ≥ 8 mmol/L, and admission to the NICU. Continuous variables were compared using student’s t-test while categorical variables were compared using chi-square or Fisher’s exact test as appropriate. Multivariable logistic regression was used to estimate the risk for elevated cord blood lactate after adjusting for maternal age and BMI. Two-sided p values < 0.05 were considered significant.
Of the 5746 patients exposed to oxytocin, 355 experienced UT one hour before delivery (6.7%). UT in the last hour was significantly associated with elevated cord blood lactate in the ‘always’ (33.5%) compared to the ‘never’ group (26%) (aOR 1.47 [1.17, 1.86]; p < 0.01) (Table 1). However, there were no differences in either umbilical arterial pH ≤ 7.10 (1.4% vs. 1.7%, aOR 0.90 [0.36, 2.24]; p = 0.67), base deficit > 8 mmol/L (5.6% vs. 4%, aOR 1.43 [0.87, 2.35], p = 0.12), or NICU admission rate (1.1% vs. 1.6%, aOR 0.72 [0.26, 1.98], p = 0.46) between the groups.
In patients experiencing uterine tachysystole immediately prior to delivery, cord blood lactate appears to be a more reliable indicator of neonatal status than pH. Future research should investigate if uterine tachysystole earlier in labor has a similar effect on cord blood lactate.