Factors affecting the dose response to oxytocin for labor stimulation

Oxytocin: physiology, pharmacology, and clinical application for labor management

Oxytocin is a peptide hormone that plays a key role in regulating the female reproductive system, including during labor and lactation. It is produced primarily in the hypothalamus and secreted by the posterior pituitary gland. Oxytocin can also be administered as a medication to initiate or augment uterine contractions. To study the effectiveness and safety of oxytocin, previous studies have randomized patients to low- and high-dose oxytocin infusion protocols either alone or as part of an active management of labor strategy along with other interventions. These randomized trials demonstrated that active management of labor and high-dose oxytocin regimens can shorten the length of labor and reduce the incidence of clinical chorioamnionitis. The safety of high-dose oxytocin regimens is also supported by no associated differences in fetal heart rate abnormalities, postpartum hemorrhage, low Apgar scores, neonatal intensive care unit admissions, and umbilical artery acidemia. Most studies reported no differences in the cesarean delivery rates with active management of labor or high-dose oxytocin regimens, thereby further validating its safety. Oxytocin does not have a predictable dose response, thus the pharmacologic effects and the amplitude and frequency of uterine contractions are used as physiological parameters for oxytocin infusion titration to achieve adequate contractions at appropriate intervals. Used in error, oxytocin can cause patient harm, highlighting the importance of precise administration using infusion pumps, institutional safety checklists, and trained nursing staff to closely monitor uterine activity and fetal heart rate changes. In this review, we summarize the physiology, pharmacology, infusion regimens, and associated risks of oxytocin.

Maximum Dose Rate of Intrapartum Oxytocin Infusion and Associated Obstetric and Perinatal Outcomes

OBJECTIVE

Despite lack of evidence for a safety threshold for oxytocin dose rate, many hospital protocols specify a maximum rate. We investigated whether exceeding 20 milliunits/min of oxytocin was associated with adverse outcomes.

METHODS

This is a secondary analysis of a double-blind, single-center, randomized controlled trial of nulliparous patients with singleton gestations at 36 weeks of gestation or later who presented in spontaneous labor randomized 1:1 to either a high-dose oxytocin titration regimen (initial-incremental rate of 6 milliunits/min) or standard-dose titration regimen (initial-incremental rate of 2 milliunits/min) for labor augmentation. A maximum oxytocin dose rate limit was not specified in the study protocol. For this secondary analysis, outcomes of participants who received oxytocin and exceeded a dose rate of 20 milliunits/min at any point in labor were compared with those whose rate remained at 20 milliunits/min or less. In addition, the cumulative proportions of labor and birth outcomes were calculated for each maximum dose rate of oxytocin reached among this study cohort.

RESULTS

Of the 1,003 participants in the parent trial, 955 (95.2%) received oxytocin, as planned, and were included, with 190 (19.9%) exceeding a maximum dose rate of 20 milliunits/min. Those who exceeded 20 milliunits/min were older and were more likely to have rupture of membranes as their trial entry indication, have hypertensive disorders of pregnancy, receive intrapartum magnesium sulfate infusion, and receive oxytocin for longer. Those whose maximum rates exceeded 20 milliunits/min underwent cesarean delivery more frequently, but the majority (74%) still delivered vaginally. In multivariable analyses, there were no significant associations between maximum oxytocin dose rates greater than 20 milliunits/min and cesarean delivery (adjusted odds ratio [aOR] 1.57, 95% CI 1.00-2.46), peripartum infection (aOR 0.69, 95% CI 0.41-1.19), postpartum hemorrhage (aOR 1.37, 95% CI 0.70-2.71), or neonatal intensive care unit (NICU) admission (aOR 1.72, 95% CI 0.89-3.31). Although 85% of spontaneous vaginal deliveries occurred at maximum oxytocin dose rates of 20 milliunits/min or less, vaginal deliveries continued to occur at higher maximum dose rates. The cumulative proportions of NICU admissions and composite severe neonatal morbidity and mortality cases increased with increasing oxytocin dose rates even with maximum oxytocin dose rates at 20 milliunits/min or less.

CONCLUSION

In multivariable analyses, there are no significant differences in maternal or perinatal adverse outcomes based on exceeding 20 milliunits/min of oxytocin. These data suggest that oxytocin dosing should be individualized to each patient and not be based on arbitrary thresholds.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov , NCT02487797.

European Guidelines on Perinatal Care - Oxytocin for induction and augmentation of labor[Formula: see text]

OF RECOMMENDATIONS1. Oxytocin for induction or augmentation of labor should not be started when there is a previous scar on the body of the uterus (such as previous classical cesarean section, uterine perforation or myomectomy when uterine cavity is reached) or in any other condition where labor or vaginal delivery are contraindicated. (Moderate quality evidence +++-; Strong recommendation).2. Oxytocin should not be started before at least 1 h has elapsed since amniotomy, 6 h since the use of dinoprostone (30 min if vaginal insert) and 4 h since the use of misoprostol (Low quality evidence ++- -; Moderate recommendation).3. Cardiotocography (CTG) should be performed and a normal pattern without tachysystole should be documented for at least 30 min before oxytocin is used. Continuous CTG, with adequate monitoring of both fetal heart rate and uterine contractions, should be maintained for as long as oxytocin is used, and thereafter until delivery (Low ++- - to moderate +++- quality evidence; Strong recommendation).4. For labor induction, at least 1-h should be allowed after amniotomy before oxytocin infusion is started, to evaluate whether adequate uterine contractility has meanwhile ensued. For augmentation of labor, if the membranes are intact and there are conditions for a safe amniotomy, the latter should be considered before oxytocin is started (Very low quality evidence +- --; Weak recommendation).5. Oxytocin should be administered intravenously using the following regimen: 5 IU oxytocin diluted in 500 mL of 0.9% normal saline (NaCl) (each mL contains 10 mIU of oxytocin), in an infusion pump at increasing rates, as shown in Table 1, until a frequency of 3-4 contractions per 10 min is reached, a non-reassuring CTG pattern ensues, or maximum rates are reached (Low quality evidence ++ - -; Strong recommendation). If the frequency of contractions exceeds 5 in 10 min, the infusion rate should be reduced, even if a normal CTG pattern is present. With a non-reassuring CTG pattern, urgent clinical assessment by an obstetrician is indicated, and strong consideration should be given to reducing or stopping the oxytocin infusion. The minimal effective dose of oxytocin should always be used. (Low ++- - to Moderate +++- - quality evidence; Strong recommendation).[Table: see text]6. Use of oxytocin for induction and augmentation of labor should be regularly audited (Low quality evidence ++--; Strong recommendation).

Oxytocin levels in low-risk primiparas following breast stimulation for spontaneous onset of labor: a quasi-experimental study

Background

Breast stimulation is performed to self-induce labor. However, there are apparently no reports on hormonal evaluation during stimulation for consecutive days in relation to induction effect. We evaluated the salivary oxytocin level following 3 consecutive days of own breast stimulation for 1 h each day compared with no breast stimulation.

Methods

We used a quasi-experimental design. The participants were low-risk primiparas between 38 and 39 gestational weeks. Eight saliva samples per participant were collected at preintervention and 30, 60, and 75 min postintervention on the first and third days. The primary outcome was change in the salivary oxytocin level on the third day after 3 consecutive days of breast stimulation for 1 h each day compared with no breast stimulation. The secondary outcomes were the rate of spontaneous labor onset and negative events including uterine hyperstimulation and abnormal fetal heart rate.

Results

Between February and September 2016, 42 women were enrolled into the intervention group (n = 22) or control group (n = 20). As there were differences in the basal oxytocin levels between the 2 groups, to estimate the change in the oxytocin level from baseline, we used a linear mixed model with a first-order autoregressive (AR1) covariance structure. The dependent variable was change in the oxytocin level from baseline. The independent variables were gestational weeks on the first day of intervention, age, education, rs53576 and rs2254298, group, time point, and interaction of group and time. After Bonferroni correction, the estimated change in the mean oxytocin level at 30 min on the third day was significantly higher in the intervention group (M = 20.2 pg/mL, SE = 26.2) than in the control group (M = − 44.4 pg/mL, SE = 27.3; p = 0.018). There was no significant difference in the rate of spontaneous labor onset. Although there were no adverse events during delivery, uterine tachysystole occurred in 1 case during the intervention.

Conclusions

The estimated change in the mean oxytocin level was significantly higher 30 min after breast stimulation on the third day. Thus, consecutive breast stimulation increased the salivary oxytocin level. Repeated stimulations likely increase the oxytocin level.

Trial registration

UMIN000020797 (University Hospital Medical Information Network; Prospective trial registered: January 29, 2016).

Factors associated with higher oxytocin requirements in labor

OBJECTIVE

To identify clinical characteristics associated with high maximum oxytocin doses in women who achieve complete cervical dilation.

METHODS

A retrospective nested case-control study was performed within a cohort of all term women at a single center between 2004 and 2008 who reached the second stage of labor. Cases were defined as women who had a maximum oxytocin dose during labor >20 mu/min, while women in the control group had a maximum oxytocin dose during labor of ≤20 mu/min. Exclusion criteria included no oxytocin administration during labor, multiple gestations, major fetal anomalies, nonvertex presentation, and prior cesarean delivery. Multiple maternal, fetal, and labor factors were evaluated with univariable analysis and multivariable logistic regression.

RESULTS

Maximum oxytocin doses >20 mu/min were administered to 108 women (3.6%), while 2864 women received doses ≤20 mu/min. Factors associated with higher maximum oxytocin dose after adjusting for relevant confounders included maternal diabetes, birthweight >4000 g, intrapartum fever, administration of magnesium, and induction of labor.

CONCLUSIONS

Few women who achieve complete cervical dilation require high doses of oxytocin. We identified maternal, fetal and labor factors that characterize this group of parturients.

Predictors of successful labor induction with oral or vaginal misoprostol

OBJECTIVE

To identify independent predictors of successful labor induction with oral or vaginal misoprostol.

METHODS

Women enrolled in four previous randomized trials involving oral or vaginal misoprostol for cervical ripening and labor induction were included in the present cohort study, with dosing of 25-50 microg every 4 to 6 h vaginally (n = 574) or 50 microg every 4 h orally (n = 207). Multiple logistic regression was performed to identify factors independently associated with successful labor induction -- defined as vaginal delivery within 12 h, vaginal delivery within 24 h and spontaneous vaginal delivery. Predictors of Cesarean birth and the need for only one dose of misoprostol were also identified. Variables included in the models were maternal age, weight, height, parity, gravidity, membrane status, route of misoprostol, gestational age, birth weight, and Bishop score and its individual components.

RESULTS

Maternal age, height, weight, parity, birth weight, dilatation, effacement and cervical station were associated with vaginal delivery within 24 h of induction. Maternal age, height, weight, nulliparity, birth weight and route of misoprostol were associated with Cesarean birth, with oral misoprostol being associated with a lower rate of Cesarean birth. The need for only one dose of misoprostol was predicted by maternal height, weight, parity, gestational age, Bishop score and route of misoprostol.

CONCLUSION

Characteristics of the woman (height, weight, parity), the fetus (birth weight) and some of the individual components of the Bishop score, were associated with successful labor induction, with oral misoprostol being associated with a lower rate of Cesarean birth.

Body mass index, Bishop score, and sonographic measurement of the cervical length as predictors of successful labor induction in twin gestations

AIMS

To evaluate the predictive value of body mass index (BMI), Bishop score, and sonographic measurement of cervical length for predicting successful labor induction (defined as an ability to achieve the active phase of labor corresponding to a cervical dilatation of > or =4 cm within 12 h of initiating oxytocin) in near-term twin gestations.

METHODS

This prospective, observational study enrolled 72 consecutive women with twin gestations at >36.0 weeks' gestation who were scheduled for induction of labor. Transvaginal ultrasound for measurement of the cervical length was performed and the Bishop score was determined by digital examination. The BMI was calculated based on the weight and height at the time of induction.

RESULTS

Labor induction was successful in 63% (45/72) of women. The mean BMI was significantly lower in women who had successfully induced labor, but no significant differences existed with respect to the mean cervical length, median Bishop score, proportion of parous and nulliparous women, and the mean total birth weight of the twin pairs between the two patient groups. Multiple logistic regression demonstrated that only BMI provided a significant contribution in predicting successful labor induction.

CONCLUSIONS

BMI independently predicted the success of labor induction in twin gestations but the sonographic measurement of the cervical length and Bishop score had poor predictive values for successful induction.

Prediction of failed labor induction in parous women at term: role of previous obstetric history, digital examination and sonographic measurement of cervical length

AIM

To examine the predictive value of previous obstetric history, Bishop score, and sonographic measurement of cervical length for predicting failed induction of labor in parous women at term.

METHODS

This prospective observational study enrolled 110 consecutive parous women at term with singleton gestations scheduled for the induction of labor. Transvaginal ultrasound for measurement of cervical length was performed and the Bishop score was assessed using digital examination. Univariate and multivariate analyses were used for statistical analysis.

RESULTS

Labor induction failed in 15 women (14%). In terms of previous obstetric history, women with only previous mid-trimester loss or preterm delivery had a significantly higher risk of failed labor induction than those with at least one previous term delivery. Logistic regression demonstrated that previous obstetric history and the Bishop score, but not cervical length, were found to be significant and independent contributing factors for failed labor induction. In the receiver operating characteristic curves, the best cut-off value of the Bishop score for the prediction of failed labor induction was 3, with a sensitivity of 73% and a specificity of 44%.

CONCLUSIONS

The previous obstetric history (i.e., only previous mid-trimester loss or preterm delivery) and the Bishop score independently predicted the failure of labor induction in parous women; however sonographic measurement of the cervical length appeared to have a poor predictive value for the risk of failed induction.

Oxytocin: new perspectives on an old drug

Oxytocin is the drug most commonly associated with preventable adverse perinatal outcomes and was recently added by the Institute for Safe Medication Practices to a small list of medications "bearing a heightened risk of harm," which may "require special safeguards to reduce the risk of error." Current recommendations for the administration of this drug are vague with respect to indications, timing, dosage, and monitoring of maternal and fetal effects. A review of available clinical and pharmacologic data suggests that specific, evidence-based guidelines for the intrapartum administration of oxytocin may be derived from available data. If implemented, such practices may reduce the likelihood of patient harm. These suggested guidelines focus on limited elective administration of oxytocin, consideration of strategies that have been shown to decrease the need for indicated oxytocin use, reliance on low-dose oxytocin regimens, adherence to specific semiquantitative definitions of adequate and inadequate labor, and an acceptance that once adequate uterine activity has been achieved, more time rather than more oxytocin is generally preferable. The use of conservative, specific protocols for monitoring the effects of oxytocin on mother and fetus is likely not only to improve outcomes but also reduce conflict between members of the obstetric team. Implementation of these guidelines would seem appropriate in a culture increasingly focused on patient safety.

Oxytocin for induction of labor

Oxytocin is the most common pharmacologic agent used for the induction and augmentation of labor. Oxytocin protocols can be divided into high-dose and low-dose protocols depending on the initial dose and the amount and rate of sequential increase in dose. Despite the frequency with which oxytocin in used in clinical practice, there is little consensus regarding which protocol is most appropriate. The purpose of this chapter is to review the most current data concerning recommendations for the use of oxytocin in the induction of labor, including cases of intrauterine fetal demise and vaginal birth after cesarean.

Factors Predicting Labor Induction Success: A Critical Analysis

Because of the risk of failed induction of labor, a variety of maternal and fetal factors as well as screening tests have been suggested to predict labor induction success. Certain characteristics of the woman (including parity, age, weight, height and body mass index), and of the fetus (including birth weight and gestational age) are associated with the success of labor induction; with parous, young women who are taller and lower weight having a higher rate of induction success. Fetuses with a lower birth weight or increased gestational age are also associated with increased induction success. The condition of the cervix at the start of induction is an important predictor, with the modified Bishop score being a widely used scoring system. The most important element of the Bishop score is dilatation. Other predictors, including transvaginal ultrasound (TVUS) and biochemical markers [including fetal fibronectin (fFN)] have been suggested. Meta-analyses of studies identified from MEDLINE, PubMed, and EMBASE and published from 1990 to October 2005 were performed evaluating the use of TVUS and fFN in predicting labor induction success in women at term with singleton gestations. Both TVUS and Bishop score predicted successful induction [likelihood ratio (LR)=1.82, 95% confidence interval (CI)=1.51-2.20 and LR=2.10, 95%CI=1.67-2.64, respectively]. As well, fFN and Bishop score predicted successful induction (LR=1.49, 95%CI=1.20-1.85, and LR=2.62, 95%CI=1.88-3.64, respectively). Although TVUS and fFN predicted successful labor induction, neither has been shown to be superior to Bishop score. Further research is needed to evaluate these potential predictors and insulin-like growth factor binding protein-1 (IGFBP-1), another potential biochemical marker.

Effect of Preeclampsia, Magnesium Sulfate Prophylaxis, and Maternal Weight on Labor Induction: A Retrospective Analysis

BACKGROUND

Our purposes were to determine the effect of preeclampsia, magnesium sulfate prophylaxis, and maternal weight on labor induction in women with preeclampsia and identify risk factors associated with its failure.

METHODS

Fifty-five preeclamptic women and 176 non-preeclamptic women requiring labor induction over an 18-month period were studied retrospectively. Prostaglandin E(2) (dinoprostone) and oxytocin were used for labor induction. Women with rupture of the membranes, spontaneous contraction resulting in cervical change, or an initial cervical examination showing more than 2 cm dilatation and 50% effacement were excluded. Statistics were analyzed with chi(2) test, Fisher's exact test, Student t test, Mann-Whitney U test, and multiple logistic regression.

RESULTS

The women with preeclampsia had a significantly higher rate of failed induction than did those without preeclampsia (p = 0.01). However, the women with preeclampsia had a higher mean maternal weight and an increased use of magnesium sulfate, and labor was induced at earlier gestational age than in those without preeclampsia (p < 0.05 for each). Multiple logistic regression showed that the use of magnesium sulfate, higher maternal weight, and unfavorable cervix, but not preeclampsia, were significantly associated with an increased risk of failed induction after correction for known confounding variables.

CONCLUSIONS

Although the risk of failed induction is increased in preeclamptic women, preeclampsia is not an independent risk factor for failed induction. The use of magnesium sulfate, higher maternal weight, and unfavorable cervix are independent risk factors for failed induction.

Induction of labor with misoprostol in pregnancies with advanced maternal age

OBJECTIVE

The objective was to compare the efficacy and complications of intravaginal misoprostol application with oxytocin infusion for induction of labor in advanced aged pregnancies with a Bishop score of < 6.

STUDY DESIGN

A hundred advanced aged (> or = 35 years) pregnant patients with a Bishop score of < 6 were randomized into two groups. The first group (50 patients) received 50 microg intravaginal misoprostol four times with 4 h intervals and the second group received oxytocin infusion for induction of labor starting from 2 mIU/min and was increased every 30 min with 2 mIU/min increments up to a maximum of 40 mIU/min. The time from induction to delivery, the route of delivery, fetal outcome, and maternal complications were recorded. Statistical analyses were performed using the Mann-Whitney U, Chi-squared and t tests to determine differences between the two groups. A p value < or = 0.05 was considered significant.

RESULTS

Misoprostol was superior for induction of labor in advanced aged pregnancies with Bishop score of < 6, as the mean time from induction to delivery was 9.61 +/- 4.12 h and 11.46 +/- 4.86 h in the misoprostol and oxytocin groups respectively, with a significant difference between the groups (p = 0.04). The rate of vaginal delivery was higher in the misoprostol group (84.0%) than in the oxytocin group (80.0%), but the difference did not reach significance (p = 0.60). The rates of placental abruption and postpartum hemorrhage were similar in both groups and no cases of uterine rupture occurred. The 1- and 5-min mean Apgar scores were 6.98 +/- 1.17 to 9.08 +/- 0.99 and 6.88 +/- 1.81 to 9.00 +/- 1.35 in the misoprostol and oxytocin groups respectively, with no significant differences between the groups (p = 0.74, p = 0.83). No cases of asphyxia were present. The rate of admission to the neonatal intensive care unit was similar in both groups.

CONCLUSION

Intravaginal misoprostol seems to be an alternative method to oxytocin in the induction of labor in advanced aged pregnant women with low Bishop scores, as it is efficacious, cheap, and easy to use. But large studies are necessary to clarify safety with regard to the rare complications such as uterine rupture.

Cervical ripening methods for labor induction

The indication for labor induction has been increasing in the world. It is known that cervical conditions are directly associated to the success of labor induction. Knowledge of cervix anatomy and physiology during pregnancy and of the different methods for cervical ripening is essential for indicating the best cervical ripening method in a given situation, therefore obtaining the best outcomes following labor induction. This is a challenge for obstetricians where not every method is readily available and accessible and C-sections rates are very high as in Brazil. Some methods are discussed in this paper including breast stimulation, membrane stripping, and the use of relaxin, oxytocin, prostaglandins, hyaluronidase, mifepristone, laminaria and Foley catheter.

Inaccuracy in cervical dilatation assessment and the progress of labour monitoring

Cervical dilatation is an essential indicator of the progress of labour and it is assessed several times during every vaginal delivery. For a long period of time, the size of the error in cervical dilatation assessment was considered of no importance and only in the last ten years it was estimated. The hypothesis is that the estimated error of +/-1cm in cervical dilatation assessment and inaccurate values for the rate of cervical dilatation, influence decisions of obstetricians during labour. It is suggested that in labours in which the rate of cervical dilatation is 1 cm/h the possibility of drawing incorrect conclusions upon progress of these labours is 11 and 33% for time intervals between assessments of 4 and 2 h.

Misoprostol versus low-dose oxytocin for cervical ripening: a prospective, randomized, double-masked trial

OBJECTIVE

A variety of cervical ripening agents exist, yet none is ideal. We performed a prospective, randomized, double-masked comparison of low-dose minimal-escalation oxytocin to misoprostol in a predominantly high-risk population.

STUDY DESIGN

Patients were allocated prospectively in a double-masked, randomized, stratified basis by an investigational pharmacist between December 1996 and December 2000 to receive either active intravenous oxytocin and placebo intravaginal misoprostol or intravenous placebo oxytocin and 50 microg of active intravaginal misoprostol. The infusion rate of oxytocin was increased from 1 to 4 mU/min; misoprostol (25 microg) was repeated at 4 hourly intervals if there were <3 uterine contractions per 10-minute interval.

RESULTS

Demographic characteristics did not differ between study groups nor did the indications for induction. Overall, the interval to delivery was less in the misoprostol group; however, vaginal delivery occurred in 61% versus 66% (not significant) of patients in the misoprostol versus oxytocin group. Indication for cesarean delivery in the misoprostol group was fetal intolerance to labor in 27% compared with 8% in the oxytocin groups (P <.05), whereas labor abnormalities were more commonly the cause in the oxytocin group versus misoprostol (26% vs 10%, P <.05). The proportion of patients was similar in each group overall and when evaluated on the basis of parity and when delivery was compared at 12, 24, and 36 hours after the initiation of cervical priming.

CONCLUSION

Our data indicate that misoprostol and low-dose minimal-escalation oxytocin appear to be equally effective for cervical priming. Low-dose oxytocin may have a preferential role in the high-risk parturient whose fetus is at increased risk for fetal intolerance to labor

Factors affecting the likelihood of successful induction after intravaginal misoprostol application for cervical ripening and labor induction

OBJECTIVE

Our purpose was to determine whether maternal age, height and weight, parity, duration of pregnancy, cervical dilatation or Bishop score, and birth weight could be used to predict the likelihood of successful induction in women given intravaginal misoprostol.

STUDY DESIGN

A computerized database was compiled of 1373 pregnancies in which intravaginal misoprostol was given for cervical ripening and labor induction. Most of these women were placed on investigational protocols in which the dose of misoprostol administered was 25 to 50 microg and the dosing intervals ranged from 3 to 6 hours. No more than 24 hours of administration was permitted. Induction was undertaken in women with unfavorable cervical examinations (Bishop scores of 4 or less) and without spontaneous labor or ruptured membranes. Univariate and stepwise multiple regression analyses were performed to identify those factors associated with successful induction, defined as vaginal delivery within 24 hours of induction.

RESULTS

Six hundred fifty-seven (48%) had successful induction. Parity (odds ratio [OR] 2.5, 95% CI 2.0-2.9, P <.0001), initial cervical dilatation (OR 1.9, 95% CI 1.6-2.3, P <.0001), Bishop score (OR 1.6, 95% CI 1.3, 1.8, P <.0001), and gestational age at entry (OR 1.3, 95% CI 1.1-1.5, P =.002) were significant at the.05 level for predicting successful induction. A multivariate stepwise logistic regression was then performed to evaluate each of these as independent predictors. Parity (OR 2.4, 95% CI 2.0-3.0, P <.0001), initial cervical dilatation (OR 1.7, 95% CI 1.4-2.1, P <.0001), and estimated gestational age (OR 1.3, 95% CI 1.1-1.6, P =.003) are significant independent predictors for successful induction, but initial Bishop score is not significant (P =.19) after adjustment for other significant predicting factors.

CONCLUSIONS

The clinical characteristics of parity, initial cervical dilatation, and gestational age at entry are predictors of the likelihood of success of cervical ripening and labor induction with intravaginal misoprostol administration.

Active management of labor: does it make a difference?

OBJECTIVE

Our goal was to evaluate whether active management of labor lowers cesarean section rates, shortens the length of labor, and overcomes any negative effects of epidural analgesia on nulliparous labor.

STUDY DESIGN

We randomly assigned 405 low-risk term nulliparous patients to either an active management of labor (n = 200) or our usual care control protocol (n = 205). Patients who were undergoing active management of labor were diagnosed as being in labor on the basis of having painful palpable contractions accompanied by 80% cervical effacement, underwent early amniotomy, and were treated with high-dose oxytocin for failure to progress adequately in labor.

RESULTS

The cesarean section rate in the active management of labor group was lower than that of controls but not significantly so (active management, 7.5%; controls, 11.7%; p = 0.36). The length of labor in the active management group was shortened by 1.7 hours (from 11.4 to 9.7 hours, p = 0.001). Fifty-five percent of patients received epidural analgesics; a reduction in length of labor persisted despite the use of epidural analgesics (active management 11.2 hours vs control 13.3 hours, p = 0.001). A significantly greater proportion of active management patients were delivered by 12 hours compared with controls (75% vs 58%, p = 0.01); this difference also persisted despite the use of epidural analgesics (66% vs 51%, p = 0.03).

CONCLUSIONS

Patients undergoing active management had shortened labors and were more likely to be delivered within 12 hours, differences that persisted despite the use of epidural analgesics. There was a trend toward a reduced rate of cesarean section.

The pharmacokinetics of oxytocin as they apply to labor induction

OBJECTIVE

Our purpose was to determine the relationship among plasma oxytocin levels, metabolic clearance rate of oxytocin, and uterine activity in gravid women undergoing labor induction.

STUDY DESIGN

Ten women receiving oxytocin for labor induction and agreeing to participate had blood sampled before initiation of oxytocin and at different levels of uterine pressure. Samples were analyzed with 200 microliter extracts from 1 ml of plasma with an oxytocin radioimmunoassay. The intraassay coefficient of variation was < 3%. Sensitivity of the assay was 1.5 pg/ml. Pharmacokinetic parameters including plasma levels and metabolic clearance rates were calculated. Data were analyzed with the paired t test and linear and logistic regression.

RESULTS

Mean oxytocin levels and metabolic clearance rates were 26.6 pg/ml and 7.97 ml/min. There was no correlation between changes in oxytocin level and metabolic clearance rate. Increases in infusion rates were correlated with increases in oxytocin levels (r = 0.71, p < 0.001). Cervical dilatation and uterine contraction pressures did not correlate with oxytocin levels.

CONCLUSION

Peripheral plasma levels of oxytocin may not accurately reflect uterine activity or progress in labor. Plasma levels of oxytocin may merely reflect the rate of oxytocin infusion.

Pharmacological Management of Labor

Normal spontaneous labor at term without maternal or fetal complications does not always occur. In these situations, pharmacological intervention is often the safest and most suitable method of delivery. The pharmacological management of labor includes the use of multiple agents that alter cervical dilatation and uterine contractions, resulting in delivery of the fetus and treatment of postpartum emergencies. This article provides a description of normal and abnormal labor patterns and possible peripartum complications. The use of oxytocin, ergot derivatives, and prostaglandins for augmentation of dysfunctional labor, induction of labor, and management of peripartum emergencies is discussed to provide information on availability of product, indications for use, clinical efficacy, potential adverse effects, and contraindications to use.