Lactate in Amniotic Fluid: Predictor of Labor Outcome in Oxytocin-Augmented Primiparas' Deliveries

Characterizing uterine responsiveness to oxytocin augmentation across four labor patterns in maternal obesity

BACKGROUND

Optimizing care during labor protraction is a key strategy for reducing cesareans, especially among people with obesity. The pathophysiology of labor dystocia remains poorly understood, limiting precise interventions targeting the cause of protraction.

METHODS

In this secondary analysis of nulliparas (n = 92) with obesity (BMI ≥ 30 kg/m2) and spontaneous labor onset, we classified labor into four phenotypes based on duration of protraction and birth route: (1) no protraction, (2) short protraction and vaginal birth, (3) extended protraction meeting criteria for labor arrest, but with eventual progression and vaginal birth, and (4) extended protraction meeting criteria for labor arrest and cesarean birth. Across these phenotypes, we compared MVU, oxytocin dose, and novel measures of uterine responsiveness to oxytocin augmentation (MVU to oxytocin dose ratios).

RESULTS

In our sample, phenotype group 1 comprised 14.1% (n = 13); group 2 comprised 30.4% (n = 28); group 3 comprised 34.8% (n = 32); and group 4 comprised 20.7% (n = 19). Uterine responsiveness to oxytocin, but not MVU, decreased with each labor phenotype. Participants with cesarean birth had the lowest uterine responsiveness to oxytocin.

CONCLUSION

Labor and birth outcomes were associated with measures of uterine responsiveness to oxytocin rather than MVU alone, and thus these may be more clinically appropriate measures for guiding clinical decision-making. Current criteria for labor arrest are likely too stringent for nulliparas with obesity, many of whom appear to progress to safe vaginal birth after longer labor durations. Differences in uterine responsiveness to oxytocin augmentation across the groups suggests underlying physiologic differences in the labor phenotypes, which should drive future research targeting pathophysiology.

New insights on labor progression: a systematic review

The past 20 years witnessed an invigoration of research on labor progression and a change of thinking regarding normal labor. New evidence is emerging, and more advanced statistical methods are applied to labor progression analyses. Given the wide variations in the onset of active labor and the pattern of labor progression, there is an emerging consensus that the definition of abnormal labor may not be related to an idealized or average labor curve. Alternative approaches to guide labor management have been proposed; for example, using an upper limit of a distribution of labor duration to define abnormally slow labor. Nonetheless, the methods of labor assessment are still primitive and subject to error; more objective measures and more advanced instruments are needed to identify the onset of active labor, monitor labor progression, and define when labor duration is associated with maternal/child risk. Cervical dilation alone may be insufficient to define active labor, and incorporating more physical and biochemical measures may improve accuracy of diagnosing active labor onset and progression. Because the association between duration of labor and perinatal outcomes is rather complex and influenced by various underlying and iatrogenic conditions, future research must carefully explore how to integrate statistical cut-points with clinical outcomes to reach a practical definition of labor abnormalities. Finally, research regarding the complex labor process may benefit from new approaches, such as machine learning technologies and artificial intelligence to improve the predictability of successful vaginal delivery with normal perinatal outcomes.

The Pathophysiology of Labor Dystocia: Theme with Variations

Abnormally prolonged labor, or labor dystocia, is a common complication of parturition. It is the indication for about half of unplanned cesarean deliveries in low-risk nulliparous women. Reducing the rate of unplanned cesarean birth in the USA has been a public health priority over the last two decades with limited success. Labor dystocia is a complex disorder due to multiple causes with a common clinical outcome of slow cervical dilation and fetal descent. A better understanding of the pathophysiologic mechanisms of labor dystocia could lead to new clinical opportunities to increase the rate of normal vaginal delivery, reduce cesarean birth rates, and improve maternal and neonatal health. We conducted a literature review of the causes and pathophysiologic mechanisms of labor dystocia. We summarize known mechanisms supported by clinical and experimental data and newer hypotheses with less supporting evidence. We review recent data on uterine preparation for labor, uterine contractility, cervical preparation for labor, maternal obesity, cephalopelvic disproportion, fetal malposition, intrauterine infection, and maternal stress. We also describe current clinical approaches to preventing and managing labor dystocia. The variation in pathophysiologic causes of labor dystocia probably limits the utility of current general treatment options. However, treatments targeting specific underlying etiologies could be more effective. We found that the pathophysiologic basis of labor dystocia is under-researched, offering wide opportunities for translational investigation of individualized labor management, particularly regarding uterine metabolism and fetal position. More precise diagnostic tools and individualized therapies for labor dystocia might lead to better outcomes. We conclude that additional knowledge of parturition physiology coupled with rigorous clinical evaluation of novel biologically directed treatments could improve obstetric quality of care.

Pharmacological Interventions in Labor and Delivery

While there is not a wide range of pregnancy-specific drugs, there are some very specific high-risk areas of obstetric care for which unique pharmacological approaches have been established. In preterm birth, labor induction and augmentation, and the management of postpartum hemorrhage, these pharmacological approaches have become the bedrock in managing some of the most common and problematic areas of antenatal and intrapartum care. In this review, we summarize the existing established and emerging evidence that supports and broadens these pharmacological approaches to obstetric management and its impact on clinical practice. It is clear that existing therapeutics are limited. They have largely been developed from our knowledge of the physiology of the myometrium and act on hormonal receptors and their signaling pathways or on ion channels influencing excitability. Newer drugs in development are mostly refinements of these two approaches, but novel agents from plants and improved formulations are also discussed.

Amniotic fluid lactate (AFL): a new predictor of labor outcome in dystocic deliveries

PURPOSE OF THIS REVIEW

Even today, hundreds of thousands of women die or suffer high levels of morbidity associated with childbirth. One of the most common causes is halted labor progress, or labor dystocia. There have been no developments in the diagnosis or treatment of dystocic deliveries since Friedman designed the Partogram in the 1950s. Oxytocin is the only treatment for dystocic labor. Sometimes, oxytocin is a lifesaver for the woman, especially in severe postpartum hemorrhages. At the same time, it is also one of the most overused drugs in obstetric care. This review article is meant to provide a short overview of the current knowledge of uterine metabolism during labor, uterine lactate production, and its association with labor dystocia. The article also intends to reflect new ways of thinking regarding practical recommendations for treating labor dystocia and offer a look at the future of dystocic labor management.

Body mass index and labor outcome associated with the level of amniotic fluid lactate. A cross-sectional study of women with labor dystocia

INTRODUCTION

Obesity is a globally growing problem. Labor dystocia is associated with obstetric complications, especially among obese pregnant women. Previous studies have shown an association between the level of lactate produced by uterine myocytes during contractions and the level of lactate in the amniotic fluid (AFL). A relationship between a high level of AFL and labor dystocia has also been demonstrated. However, it is still unknown whether the observation applies to all women with labor dystocia, regardless of body mass index (BMI). Aims: This study investigated whether there was any difference in the level of AFL in the three BMI groups and whether there was a difference in labor outcomes between high and low AFL in the different groups.

MATERIALS AND METHODS

This cross-sectional study included 1683 women from three different countries. Healthy nulliparous women in active labor were included, and they were grouped according to BMI as normal weighted (<25), overweight (≥25-29), and obese (≥30), respectively. AFL was categorized as high (≥10.1 mmol/l) and low (<10.1 mmol/l). The main outcome was the frequency of cesarean section.

RESULTS

No difference in AFL levels was found between the three BMI groups at delivery (mean values of 8.2 vs. 8.3 vs. 8.4 mmol/l, p = .3). Obese women with high AFL had a higher frequency of cesarean section than normal-weighted women (16.2 vs. 20.7 vs. 29.2%). Other risk factors associated with cesarean section varied among the different BMI groups.

CONCLUSIONS

This study showed no difference in the mean level of AFL between women with different BMIs. Further, high AFL was associated with a higher frequency of cesarean section in all three BMI groups, suggesting that the level of AFL can in the future be used as a predictor of labor outcome among women with labor dystocia despite their BMI.

Incidence and determinants of perinatal mortality among women with obstructed labour in eastern Uganda: a prospective cohort study

BACKGROUND

In Uganda, the incidence and determinants of perinatal death in obstructed labour are not well documented. We determined the incidence and determinants of perinatal mortality among women with obstructed labour in Eastern Uganda.

METHODS

Between July 2018 and September 2019, 584 with obstructed labour were recruited and followed up to the 7th day postnatal. Information on maternal characteristics, obstetric factors and laboratory parameters was collected. Each patient received the standard perioperative care. We used a generalized linear model for the Poisson family, with a log link and robust variance estimation to determine the association between the exposure variables and perinatal death.

RESULTS

Of the 623 women diagnosed with obstructed labour, 584 met the eligibility criteria. There were 24 fresh still births (FSB) and 32 early neonatal deaths (ENND) giving an FSB rate of 43.8 (95% CI 28.3-64.4) deaths per 1000 total births; early neonatal death rate of 58.4 (95% CI 40.3-81.4) deaths per 1000 and an overall perinatal mortality rate of 102.2 (95% CI 79.4-130.6) deaths in the first 7 days of life. A mother being referred in active labour adjusted risk ratio of 2.84 (95% CI: 1.35-5.96) and having high blood lactate levels at recruitment adjusted risk ratio 2.71 (95% CI: 1.26-4.24) were the determinants of perinatal deaths.

CONCLUSIONS

The incidence of perinatal death was four times the regional and national average. Babies to women referred in active labour and those with high maternal blood lactate were more likely to die.

Amniotic fluid lactate level as a diagnostic tool for prolonged labour

Prolonged labour can lead to postpartum complications and adverse outcomes for both mother and baby. Measurable parameters can help in the active management of labour, timely diagnosis of dystocia and in the choice of the method of delivery. Progressive uterine contractions are necessary to complete labour successfully. Myometrial fatigue during prolonged labour causes a change from aerobic to anaerobic metabolism, resulting in an accumulation of intramuscular lactic acid and probably a subsequent increase in amniotic fluid lactate concentration. High amniotic fluid lactate level has been associated with ineffective uterine contractions leading to labour arrest. A considerable number of studies conducted so far indicate that the level of lactate in amniotic fluid may be a new non-invasive diagnostic tool for early prediction of prolonged labour and the need for immediate obstetric intervention. Low amniotic fluid lactate level may facilitate a decision to continue vaginal labour by oxytocin augmentation. A high level of amniotic fluid lactate is associated with surgical obstetric procedures. Measuring amniotic fluid lactate level might simplify the patient's allocation to a group, which will benefit from the administration of oxytocin and to a group that will not benefit from further prolongation of labour. This study aimed to briefly review current knowledge on amniotic fluid lactate concentrations measured using standard biochemical methods during the first stage of labour following normal pregnancy, as a possible diagnostic tool for prolonged labour. For this purpose, PubMed, EMBASE, Medline (1990 to July 2020) trials register and reference lists of relevant articles were searched.

Fetal heart rate monitoring in labor: from pattern recognition to fetal physiology

The journey of human labor involves hypoxic and mechanical stresses as a result of progressively increasing frequency, duration and strength of uterine contractions and resultant compression of the umbilical cord. In addition, occlusion of the spiral arteries during myometrial contractions also leads to repetitive interruptions in the utero-placental circulation, predisposing a fetus to progressively worsening hypoxic stress as labor progresses. The vast majority of fetuses are equipped with compensatory mechanisms to withstand these hypoxic and mechanical stresses. They emerge unharmed at birth. However, some fetuses may sustain an antenatal injury or experience a chronic utero-placental insufficiency prior to the onset of labor. These may impair the fetus to compensate for the ongoing hypoxic stress secondary to ongoing uterine contractions. Non-hypoxic pathways of neurological damage such as chorioamnionitis, fetal anemia or an acute fetal hypovolemia may potentiate fetal neurological injury, especially in the presence of a super-imposed, additional hypoxic stress. The use of utero-tonic agents to induce or augment labor may increase the risk of hypoxic-ischemic injury. Clinicians need to move away from "pattern recognition" guidelines ("normal," "suspicious," "pathological"), and apply the knowledge of fetal physiology to differentiate fetal compensation from decompensation. Individualization of care is essential to optimize outcomes.

Randomized controlled trial of oral bicarbonate treatment for labor stagnation

AIM

The aim of this study was to determine the effect of oral sodium bicarbonate solution on delivery outcome of primiparous women with labor stagnation.

METHODS

This randomized controlled trial study was performed on 142 primiparous pregnant women referred to Jiroft University hospitals who had stagnation during labor. In the intervention group, in addition to oxytocin, 4.26 g of sodium bicarbonate dissolved in 200 mL of water were given orally. The control group received only oxytocin. Data were analyzed by t-test and chi-square test.

RESULTS

The mean interval of dilatation stopping to delivery in the intervention group was significantly lower than the control group (202.34 vs 304.08 min, P = 0.001). The mean duration of the first and second stages of labor in the intervention group was lower than the control group (280.44 vs 397.16 and 35.00 vs 51.72 min respectively, P = 0.001). There was no statistically significant difference between the intervention and control groups in the rate of cesarean section and Apgar score. In the intervention group, the rate of spontaneous delivery was significantly higher (65 vs 56 cases, P = 0.03) than the control group.

CONCLUSION

The results of the present study could suggest the use of oral bicarbonate in stagnation as a cheap and no-cost method to facilitate normal vaginal delivery.

How much synthetic oxytocin is infused during labour? A review and analysis of regimens used in 12 countries

Objective

To compare synthetic oxytocin infusion regimens used during labour, calculate the International Units (IU) escalation rate and total amount of IU infused over eight hours.

Design

Observational study

Setting

Twelve countries, eleven European and South Africa.

Sample

National, regional or institutional-level regimens on oxytocin for induction and augmentation labour

Methods

Data on oxytocin IU dose, infusion fluid amount, start dose, escalation rate and maximum dose were collected. Values for each regimen were converted to IU in 1000ml diluent. One IU corresponded to 1.67μg for doses provided in grams/micrograms. IU hourly dose increase rates were based on escalation frequency. Cumulative doses and total IU amount infused were calculated by adding the dose administered for each previous hour. Main Outcome Measures Oxytocin IU dose infused

Results

Data were obtained on 21 regimens used in 12 countries. Details on the start dose, escalation interval, escalation rate and maximum dose infused were available from 16 regimens. Starting rates varied from 0.06 IU/hour to 0.90 IU/hour, and the maximum dose rate varied from 0.90 IU/hour to 3.60 IU/hour. The total amount of IU oxytocin infused, estimated over eight hours, ranged from 2.38 IU to 27.00 IU, a variation of 24.62 IU and an 11-fold difference.

Conclusion

Current variations in oxytocin regimens for induction and augmentation of labour are inexplicable. It is crucial that the appropriate minimum infusion regimen is administered because synthetic oxytocin is a potentially harmful medication with serious consequences for women and babies when inappropriately used. Estimating the total amount of oxytocin IU received by labouring women, alongside the institution’s mode of birth and neonatal outcomes, may deepen our understanding and be the way forward to identifying the optimal infusion regimen.

An Integrated Review of Uterine Activity Monitoring for Evaluating Labor Dystocia

Introduction:

Labor dystocia is the most common cause of cesarean birth in the United States, yet how dystocia develops during labor remains elusive. Uterine activity monitoring has significant potential for advancing our understanding of labor dystocia. While evaluating contraction frequency and amplitude is a common component of labor dystocia management, the literature describing the relationship between measures of uterine activity and labor dystocia is heterogeneous and has not been synthesized to identify the best methods for use in clinical investigation.

Methods:

We conducted a literature search for original research exploring the relationship between uterine activity and labor dystocia published between 2000 and 2019. Included articles were critically reviewed and synthesized.

Results:

Across 11 identified studies, investigators employed 3 different techniques for monitoring uterine activity and 9 different measures were employed. Uterine activity measures, including Montevideo units, uterine electromyography power density spectrum and sample entropy, and the fall-to-rise ratio of contraction shape, detected patterns associated with labor dystocia or cesarean birth.

Discussion:

The use of multiple regression with clinical covariates and a uterine activity measure increased the accuracy of predicting cesarean delivery. Uterine electromyography may be especially useful to evaluate labor dystocia phenotypes to differentiate uterine muscle fatigue from understimulation and lead to algorithms for increased precision in the diagnosis of labor dystocia and innovative approaches to treatment.

Effects of Increased Frequency, High Dose, and Pulsatile Oxytocin Regimens on Abnormal Labor Delivery

Background

The current guideline for oxytocin regimens in the abnormal labor of delivery is continuous infusion. The objective of the present study was to compare effects and safety measures of various available regimens of oxytocin in abnormal labor delivery.

Material/Methods

In this clinical experimental study, a total of 900 pregnant women admitted for delivery were randomized into 5 group with 162 each. Pregnant women received oxytocin as continuous administration of 16 mU/min (Group I), 1 mU/min (group II), 4 mU/min (group III), 5 mU/min quarter-hourly (group IV), and through a syringe pump (group V). Measurement of the expense of delivery, the ratio of the instrumental delivery, and the other secondary outcome measures was performed to find the best regimen of oxytocin. The 2-tailed paired t test and Mann-Whitney U test following Dunnett’s multiple comparison tests were used at 95% confidence level.

Results

Pulsatile delivery had least risk of instrumental delivery as compared to continuous infusion (p<0.0001, q=6.663) and normal-frequency low-dose (p<0.0001, q=5.638) of oxytocin. The time required from infusion to delivery was longer for group II (p=0.001, q=2.925), group IV (p<0.0001, q=4.829), and group V (p<0.0001, q=41.456) than for group I. The expense of delivery was: group I < group II < group IV < group III < group V.

Conclusions

High-dose and pulsatile preparation of oxytocin had reduced risks of operative delivery vs. continuous administration.

A randomized controlled trial of a new treatment for labor dystocia

OBJECTIVE

Labor dystocia is an intransigent, high-profile issue in obstetric care. Amniotic fluid lactate (AFL) reflects the uterine metabolic status. High levels associate with subsequent need for operative intervention due to dystocia. In sports medicine, it is known that lactic acid can affect muscular performance and can be decreased by bicarbonate given orally before physical activity.

MATERIAL AND METHODS

Two hundred dystocic deliveries were included. At the confirmation of dystocia, the AFL-level was analyzed. Deliveries were randomized to an intake of bicarbonate or not. In the "non-bicarbonate-group", stimulation with oxytocin was started immediately. In the "bicarbonate-group", bicarbonate was given; and oxytocin was started 1 hour after the intake. New sampling of AF was performed after 1 hour in both groups.

OUTCOME MEASURED

if an oral intake of bicarbonate changes the AFL levels and enhances delivery outcome in dystocic deliveries.

RESULTS

Bicarbonate decreases the AFL levels (p < .001). The spontaneous vaginal delivery rate after treatment with bicarbonate was increased (p = .007), without affecting the fetal outcome.

CONCLUSIONS

An increase of spontaneous vaginal deliveries resulted from bicarbonate ingestion by dystocic women. A decreased level of AFL-level was shown. This simple, low cost treatment has the potential to improve maternal morbidity and satisfaction worldwide.