Association between Uterine Tachysystole during the Last Hour of Labor and Cord Blood Lactate in Parturients at Term Gestation

Objective: To assess whether uterine tachysystole (UT) in labor causes an increase in cord blood lactate.

Study design: 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. Patients with UT in the last hour ("always") were compared with those without UT ("never"). 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 neonatal intensive care unit (NICU). Multivariable logistic regression was used to estimate the risk for elevated cord blood lactate after adjusting for maternal age and body mass index.

Results: Of the 8,580 patients included in the analysis, 513 experienced UT 1 hour before delivery (5.9%). UT was significantly associated with elevated cord blood lactate in the "always" (33.5%) compared with the "never" group (26%) (adjusted odds ratio 1.47 [1.17, 1.86]; p < 0.01). However, there were no differences in either umbilical arterial pH, base deficit, or NICU admission rates.

Conclusion: UT in the last hour preceding delivery increases arterial cord blood lactate suggesting that UT proximate to delivery should be considered as a variable when interpreting cord blood gas values.