Umbilical cord gas analysis: clinical implications of a comprehensive, contemporary determination of normal ranges.

BACKGROUND: Umbilical cord gases are often used to assess the impact of labor and delivery on the fetus. However, no large series exists that reflects contemporary obstetrical practice or that analyzed blood gas ranges by route of delivery. Baseline, prelabor acid-base status in the human fetus is also poorly defined, rendering the assessment of blood gas changes during labor difficult. OBJECTIVE: This study aimed to define normal umbilical cord gas and lactate values, stratified by mode of delivery, in a large contemporary series in which universal umbilical cord gas evaluation was dictated by protocol. STUDY DESIGN: This was a retrospective cohort study. We analyzed the umbilical cord gas and lactate data of an unselected population of infants born between March 2012 and April 2022 at a large teaching hospital. These values were then analyzed by mode of delivery and, for cesarean deliveries, by indication for cesarean delivery and type of anesthesia. Umbilical cord gas values from infants delivered by elective cesarean delivey under general anesthesia without labor were considered representative of baseline, prelabor values. RESULTS: Data were available for 45,475 infants. The median arterial pH values and interquartile ranges for vaginal births, elective cesarean deliveries without labor, and cesarean deliveries performed for fetal heart rate concerns were 7.27 (0.09), 7.27 (0.06), and 7.25 (0.09), respectively. Arterial lactate values for these same 3 groups were 4.1 (2.5), 2.5 (1.2), and 4.0 (2.8) mmoles/L, respectively. Because of the very large sample size, most comparisons yielded differences that were statistically significant, but clinically irrelevant. Of all the infants, 14% had an arterial pH <7.20; a pH value of 7.1 represents 2 standard deviations from the mean. CONCLUSION: This large, population-based study of umbilical cord gas and lactate levels in an unselected population, stratified by delivery mode, represents a previously unavailable benchmark for the evaluation of umbilical cord gases. Arterial umbilical cord pH values for infants delivered by elective caesarean delivery without labor (median pH 7.28) reflect a lower prelabor fetal pH baseline than previously assumed. This finding, coupled with our determination that a 2 standard deviation below normal pH limit of 7.1, instead of the historic arbitrary pH of 7.2 threshold, helps to explain the poor positive predictive value of electronic fetal heart rate monitoring, a test designed to detect arterial pH levels that have fallen from an assumed baseline near pH 7.4 to an assumed potentially injurious pH level of <7.2. Uncomplicated labor, even when prolonged, does not generally lead to a clinically significant cumulative hypoxic stress to the human fetus. These findings, along with our determination that there is no difference in the acid-base status among infants delivered by cesarean delivery for fetal heart rate concerns, help to explain the failure of current approaches in labor and delivery management to reduce the rates of neonatal hypoxic-ischemic encephalopathy and cerebral palsy, conditions that almost always reflect developmental events rather than the effects of labor on the fetus.

Examining the effect of quality improvement initiatives on decreasing racial disparities in maternal morbidity.

The objective of this study was to evaluate the impact of quality improvement (QI) and patient safety initiatives and data disaggregation on racial disparities in severe maternal morbidity from hemorrhage (SMM-H).Our hospital began monitoring and reporting on SMM-overall and SMM-H rates in 2018 using administrative data. In March 2019, we began stratifying data by race and ethnicity and noted a disparity in rates, with non-Hispanic Black women having the highest SMM rates. The data was presented as run charts at monthly department meetings. During this time, our hospital implemented several QI and patient safety initiatives around obstetric hemorrhage and used the stratified data to inform guideline development to reduce racial disparity. The initiatives included implementation of a hemorrhage patient safety bundle and in-depth case reviews of adverse patient outcomes with a health equity focus. We then retrospectively analyzed our data. Our outcome of interest was SMM-H prior to data stratification (pre-intervention: June 2018-February 2019) as compared to after data stratification (post-intervention: March 2019-June 2020).During our study time period, there were 13,659 deliveries: 37% Hispanic, 35% White, 20% Black, 7% Asian and 1% Other. Pre-intervention, there was a statistically significant difference between Black and White women for SMM-H rates (p<0.001). This disparity was no longer significant post-intervention (p=0.138). The rate of SMM-H in Black women decreased from 45.5% to 31.6% (p=0.011).Our findings suggest that QI and patient safety efforts that incorporate race and ethnicity data stratification to identify disparities and use the information to target interventions have the potential to reduce disparities in SMM.

Relationship Between Umbilical Cord Gas Values and Neonatal Outcomes: Implications for Electronic Fetal Heart Rate Monitoring.

OBJECTIVE: To evaluate the relationship between umbilical artery cord gas values and fetal tolerance of labor, as reflected by Apgar score. We hypothesized the existence of wide biological variability in fetal tolerance of metabolic acidemia, which, if present, would weaken one fundamental assumption underlying the use of electronic fetal heart rate (FHR) monitoring. METHODS: We conducted a retrospective cohort study of term, singleton, nonanomalous fetuses delivered in our institution between March 2012 and July 2020. Universally obtained umbilical cord gas values and Apgar scores were extracted. We calculated Spearman correlation coefficients and receiver operating characteristic curves for various levels of umbilical artery pH, base excess, and Apgar scores. RESULTS: We analyzed data from 29,787 deliveries. The statistical correlation between umbilical artery pH and base excess and both 1- and 5-minute Apgar scores was weak or nonexistent in all pH range subgroups (range 0.064-0.213). Receiver operating characteristic curve analysis suggested umbilical artery pH value of 7.22 yields the best discrimination for prediction of a severely depressed newborn (5-minute Apgar score less than 4), but sensitivity and specificity for this predictive value remains poor to moderate. CONCLUSION: The use of electronic FHR monitoring is predicated on a documented relationship between FHR patterns and umbilical artery pH, and an assumed correlation between pH and fetal outcomes, reflecting fetal tolerance of labor and delivery. Our data demonstrate a weak-to-absent correlation between metabolic acidemia and even short-term fetal condition, thus significantly weakening this latter assumption. No amount of future modification of FHR pattern interpretation to better predict newborn pH is likely to lead to improved newborn outcomes, given this weakness in a fundamental assumption on which FHR monitoring is based.

Pathophysiologic Origins of Brachial Plexus Injury.

OBJECTIVE: To analyze the origins and consequences of cases of brachial plexus injuries and their relationship to shoulder dystocia. METHODS: We conducted a retrospective cohort study and identified all neonates with brachial plexus injury delivered at our institution between March 2012 and July 2019. A review was performed of the maternal and neonatal records of each neonate to identify obstetric antecedents, including the occurrence of shoulder dystocia and persistence of the injury. Experience of the delivering clinician was also examined. Statistical analysis was performed with the Fisher exact test, χ test for trends, and two-tailed t tests. RESULTS: Thirty-three cases of brachial plexus injury were identified in 41,525 deliveries (0.08%). Fourteen (42%) of these cases were not associated with shoulder dystocia; three (9%) followed cesarean delivery. Brachial plexus injury without shoulder dystocia was related to the absence of maternal diabetes, lower birth weights, and a longer second stage of labor. Persistent brachial plexus injury at the time of discharge was seen with equal frequency among neonates with (17/19, 89%, 95% CI 0.52-100%) and without shoulder dystocia (10/14, 71%, 95% CI 34-100%), P=.36). Whether brachial plexus injury was transient or persistent after shoulder dystocia was unrelated to the years of experience of the delivering clinician. Despite ongoing training and simulation, the already low incidence of brachial plexus injury did not decrease over time at our institution. CONCLUSION: Brachial plexus injury and shoulder dystocia represent two complications of uterine forces driving a fetus through the maternal pelvis in the presence of disproportion between the passage and the shoulder girdle of the passenger. Either or both of these complications may occur, but often are not causally related.

An Initiative to Reduce the Episiotomy Rate: Association of Feedback and the Hawthorne Effect With Leapfrog Goals.

OBJECTIVE: To assess the association of education, performance feedback, and the Hawthorne effect with a reduction in the episiotomy rate in a large academic institution. METHODS: We describe a prospective observational study of a project conducted between March 2012 and February 2017 to assist clinicians in meeting the Leapfrog Group (www.leapfroggroup.org) target rates for episiotomy. Phases of this project included preintervention (phase 1, March 2012 to April 2014), education and provision of collective department episiotomy rates (phase 2, May 2014 to December 2014), ongoing education with emphasis on a revised Leapfrog target rate (phase 3, January 2015 to February 2016), and provision of individual episiotomy rates to practitioners on a monthly basis (phase 4, March 2016 to February 2017). We analyzed the department episiotomy rates before, during, and after these efforts. Cases of shoulder dystocia were excluded from this analysis. Statistical analysis was performed using a two-tailed Student t test and χ test with P<.05 considered significant. RESULTS: During the study period 1,176 episiotomies were performed in 16,441 vaginal deliveries (7.2%). In phase 2 (2,352 vaginal deliveries), there was a nonsignificant drop in the episiotomy rate with education alone (9.0-8.2%, P=.21). In phase 3 (4,379 vaginal deliveries), the episiotomy rate demonstrated an additional, significant drop to 5.9% (P<.001), but this reduction did not reach the new Leapfrog goal of 5%. In phase 4 (3,160 vaginal deliveries), the hospital episiotomy rate again dropped significantly from 5.9% to 4.37% (P=.007) and met the target rate of 5%. This reduction was sustained over a 12-month time period. During this same time period, the rate of operative vaginal delivery among vaginal births increased (4.5-5.4%, P=.003) and there was no significant change in the rates of third- and fourth-degree perineal laceration (3.8-3.3%, P=.19). CONCLUSION: Education, performance feedback, and the Hawthorne effect were associated with a reduction in the episiotomy rate in a large academic institution without a reduction in the rate of operative vaginal delivery or an increase in the rate of third- and fourth-degree lacerations.