Influence of the pelvic outlet capacity on fetal head presentation at delivery

The second stage of labor

The second stage of labor extends from complete cervical dilatation to delivery. During this stage, descent and rotation of the presenting part occur as the fetus passively negotiates its passage through the birth canal. Generally, descent begins during the deceleration phase of dilatation as the cervix is drawn upward around the fetal presenting part. The most common means of assessing the normality of the second stage of labor is to measure its duration, but progress can be more meaningfully gauged by measuring the change in fetal station as a function of time. Accurate clinical identification and evaluation of differences in patterns of fetal descent are necessary to assess second stage of labor progress and to make reasoned judgments about the need for intervention. Three distinct graphic abnormalities of the second stage of labor can be identified: protracted descent, arrest of descent, and failure of descent. All abnormalities have a strong association with cephalopelvic disproportion but may also occur in the presence of maternal obesity, uterine infection, excessive sedation, and fetal malpositions. Interpretation of the progress of fetal descent must be made in the context of other clinically discernable events and observations. These include fetal size, position, attitude, and degree of cranial molding and related evaluations of pelvic architecture and capacity to accommodate the fetus, uterine contractility, and fetal well-being. Oxytocin infusion can often resolve an arrest or failure of descent or a protracted descent caused by an inhibitory factor, such as a dense neuraxial block. It should be used only if thorough assessment of fetopelvic relationships reveals a low probability of cephalopelvic disproportion. The value of forced Valsalva pushing, fundal pressure, and routine episiotomy has been questioned. They should be used selectively and where indicated.

Sonographic risk assessment for an unplanned operative delivery: a prospective study

PURPOSE

To assess the value of pre-labor maternal and fetal sonographic variables to predict an unplanned operative delivery.

METHODS

In this prospective study, nulliparous women were recruited at 37.0-42.0 weeks of gestation. Sonographic measurements included estimated fetal weight, maternal pubic arch angle, and the angle of progression. We performed a descriptive and comparative analysis between two outcome groups: spontaneous vaginal delivery (SVD) and unplanned operative delivery (UOD) (vacuum-assisted, forceps-assisted and cesarean deliveries). Multivariate logistic regression with ROC analysis was used to create discriminatory models for UOD.

RESULTS

Among 234 patients in the study group, 175 had a spontaneous vaginal delivery and 59 an unplanned operative delivery. Maternal height and pubic arch angle (PAA) significantly correlated with UOD. Analysis of Maximum Likelihood Estimates revealed a multivariate model for the prediction of UOD, including the parameters of maternal age, maternal height, sonographic PAA, angle of progression (AOP), and estimated fetal weight, with an area under the curve of 0.7118.

CONCLUSION

Sonographic parameters representing maternal pelvic configuration (PAA) and maternal-fetal interface (AOP) improve the prediction ability of pre-labor models for a UOD. These data may aid the obstetrician in the counseling process before delivery.

Fetal head malposition and epidural analgesia in labor: a case-control study

BACKGROUND

The fetal head malposition in labor leads to prolonged labor, cesarean delivery and increased perinatal morbidity. Epidural analgesia has been associated with fetal head malposition, but it remains unknown if this relation is causal.

OBJECTIVE

To compare the incidence of fetal malposition during labor and maternal/fetal outcomes, between women who received epidural analgesia with those who did not use the analgesic method.

STUDY DESIGN

Case control study including 500 women with a single fetus in vertex position who gave birth at term at the Policlinic Hospital of Modena between May 2019 and July 2019. Two-hundred and fifty women belonged to the epidural analgesia (EA) group and 250 to the control group.

RESULTS

The rate of posterior occiput positions occurred 4 times more frequently in the EA group than in the control group (8.8% vs 2.2%, p = .004). Cesarean sections were significantly higher in the EA group (11.6% vs 1.6%, p < .0000) as well as the need for augmentation with oxytocin (20% vs 8%, p = .0001) compared to the control group, in which spontaneous delivery prevailed instead. Women with epidural had labors that lasted on average 7.0 h against the 3.30 h of controls (p < .0000). The length of 2nd stage of labor was 55 vs 30 min (p = .009), respectively. No differences in blood loss and Apgar score between groups. Early breastfeeding was significantly higher among controls (82% vs 92.8%, p = .0004).

CONCLUSIONS

Women receiving epidural analgesia in labor have higher rate of fetal malposition, prolonged labors, and more cesarean sections than controls. However, further studies are required to confirm a causal association between EA and fetal head malposition.

Intrapartum ultrasound monitoring of malposition and malrotation during labor neuraxial analgesia: maternal outcomes

Objective: This study analyzes the important role of ultrasonography (IUS) related to the maternal outcomes in women with fetal persistent occiput posterior position (POPP) and asynclitism (A) in labor neuraxial analgesia (LNA).Study design: Prospective assessment of 148 primiparous women diagnosed with the prolonged second stage of labor. Transabdominal and transperineal IUS were used to detect fetal head position and to evaluate the angle of progression (AOP) and pubic arch angle (PAA). Statistical data about maternal aspects, modalities of delivery and maternal outcomes were observed.Results: In all parturients included in the study, the operative delivery rate was 73%. In patients delivered via cesarean section, the PAA was ≤ of 96.5°. There was statistical correlation between doses of LNA and Apgar score at first minute (r0.8).Conclusions: There is a greater frequency of Fetal POPP and asynclitism related with maternal complications. The results of our study confirmed the importance of determination of angle of progression (AoP) and PAA in the prolonged second stage of labor. Unfavorable AoP and PAA, in presence of POPP and A, are related with high percentage of operative delivery. If the prolonged labor and delivery in these patients exceed time limit proposed by American College of Obstetricians and Gynecologists guidelines, it may be viewed as a possible malpractice. In cases of POPP with asynclitism, in the second stage of labor detected by IUS it is advisable to discontinue the anesthetic drugs administration in LNA; because the labor pain is related to the dystocia, an operative delivery is necessary to avoid maternal and fetal complications.

Incidence of cesarean section and analysis of risk factors for failed conversion of labor epidural to surgical anesthesia: A prospective, observational study in a tertiary care center

BACKGROUND AND AIMS

This study aimed to analyze the effect of labor epidural (LE) on the incidence of cesarean section (CS) and assess the risk factors involved in failed conversion of LE to surgical anesthesia for CS.

MATERIAL AND METHODS

A prospective observational study of 18 months from January 2012 to June 2013 was conducted on all patients who had delivered in the labor room suit of our hospital. The data collected for all 4694 patients included their demographics, parity and mode of delivery. In addition a predesigned proforma, with additional information was used for 629 parturient with LE.

RESULTS

During the study period, total numbers of deliveries performed in our hospital were 4694, with an epidural rate of 13.4% (629/4694). No significant difference (P = 0.06) was observed in the rate of CS among women with or without LE (28 % [n = 176/629] vs. 31.7 % [n = 1289/4065]), however, a statistically significant difference (P < 0.01) was observed in the rate of assisted delivery in patients receiving LE as compared to those delivering without it (8.7% [n = 55/629] vs. n = 3.7% [154/4065]). For 176 patients requiring CS, LE utilization for surgical anesthesia was 52.8% (93/176) and factors identified for not utilizing LE in 47% (83/176) were; failure to achieve surgical anesthesia in 6.8% (12/176), emergency CS in 28.4% (50/176), patient preference in 6.8% (12/176) and inadequate labor pain relief with LE in 5.1% (9/176) patients. Non-obstetric anesthesiologists were involved in 59% (49/83) of cases where LE was not used for CS.

CONCLUSION

LE had no effect on the rate of CS; however it significantly increased (P < 0.01) the rate of assisted delivery. Factors like inadequate LE, emergency situations and non-obstetric anesthesiologists can all be responsible for failed conversion of LE to surgical anesthesia for CS.

Persistent occiput posterior

Persistent occiput posterior (OP) is associated with increased rates of maternal and newborn morbidity. Its diagnosis by physical examination is challenging but is improved with bedside ultrasonography. Occiput posterior discovered in the active phase or early second stage of labor usually resolves spontaneously. When it does not, prophylactic manual rotation may decrease persistent OP and its associated complications. When delivery is indicated for arrest of descent in the setting of persistent OP, a pragmatic approach is suggested. Suspected fetal macrosomia, a biparietal diameter above the pelvic inlet or a maternal pelvis with android features should prompt cesarean delivery. Nonrotational operative vaginal delivery is appropriate when the maternal pelvis has a narrow anterior segment but ample room posteriorly, like with anthropoid features. When all other conditions are met and the fetal head arrests in an OP position in a patient with gynecoid pelvic features and ample room anteriorly, options include cesarean delivery, nonrotational operative vaginal delivery, and rotational procedures, either manual or with the use of rotational forceps. Recent literature suggests that maternal and fetal outcomes with rotational forceps are better than those reported in older series. Although not without significant challenges, a role remains for teaching and practicing selected rotational forceps operations in contemporary obstetrics.

A New Method to Measure the Subpubic Arch Angle Using 3-D Ultrasound

Objectives: The aim of this study was to assess the reproducibility of both a new contrast-enhancing technique (Oblique View eXtended Imaging, OVIX; Samsung) and the recently reported 3-D multiplanar technique (MPT) in the measurement of the subpubic angle (SPA) among a group of women at term gestation. In addition, we aimed to study the intermethod agreement between the OVIX technique and MPT. Methods: We acquired a transperineal 3-D ultrasound volume from 155 women with a singleton uncomplicated term pregnancy before the onset of labor. Each 3-D dataset was analyzed by the MPT and OVIX algorithm. The angle formed by the lower edges of the pubic rami (SPA) was measured twice by an operator and once by another operator for each technique in order to assess intra- and interobserver reproducibility. Reproducibility and intermethod agreement were studied by means of the intraclass correlation coefficient (ICC) and Bland-Altman method. Results: SPA measurements performed with OVIX showed high intraobserver [ICC 0.912, 95% confidence interval (CI) 0.882-0.935] and good interobserver (ICC 0.791, 95% CI 0.724-0.844) agreement, while those measured with MPT showed moderate intraobserver (ICC 0.573, 95% CI 0.457-0.670) and good interobserver (ICC 0.640, 95% CI 0.537-0.724) agreement. Whereas the intermethod analysis showed good agreement between the MPT and the OVIX techniques (ICC 0.614, 95% CI 0.414-0.757), the SPA measured by MPT were significantly wider than those measured by OVIX (125 ± 12 vs. 120 ± 11°, p = 0.006). Conclusions: OVIX is a reliable technique for SPA measurement. MPT overestimates the SPA in comparison with OVIX. Further studies are needed to assess its clinical utility.

Pubic arch angle in prolonged second stage of labor: clinical significance

OBJECTIVE

To evaluate the clinical significance of the pubic arch angle (PAA) measured by transperineal ultrasound during prolonged second stage of labor.

METHODS

We evaluated prospectively 62 women ≥ 37 weeks of gestation with failure to progress in the second stage of labor. Transperineal ultrasound (transverse plane) was used to measure the pubic arch angle. Correlations with fetomaternal characteristics, mode of delivery and perinatal outcome were evaluated.

RESULTS

The mean PAA was 101.1° (± 13.1°; range, 80°-135°). We found a negative correlation with maternal age. Patients with an occipitotransverse fetal position had a significantly smaller angle compared with those with occipitoanterior positions (94.3° ± 5.5° vs. 103.2° ± 14.8°, P < 0.05), as did those with operative deliveries compared with those with spontaneous vaginal delivery (97.1° ± 11.5° vs. 110.1° ± 14.0°, P < 0.05). The prediction of operative delivery in prolonged second stage of labor by receiver-operating characteristics curve using PAA alone yielded an area under the curve of 0.75. The predicted probability for operative delivery increased as PAA decreased, with an odds ratio of 0.933 for each decrease in angle of 1°.

CONCLUSION

Our study suggests a correlation between the PAA and mode of delivery in prolonged second stage of labor. This may be used as an adjunctive parameter when considering delivery mode.

Estimating the impact of pelvic immaturity and young maternal age on fetal malposition

OBJECTIVE

Fetal malposition, specifically occiput posterior and transverse (OP/OT), is associated with higher intra-partum morbidity. We tested the hypothesis that young maternal age and pelvic immaturity are risk factors for fetal malposition.

METHODS

In a cohort study of all nulliparous teen (≤18 years) deliveries over a 4-year period at one institution, fetal head position at time of delivery was collected and correlated with maternal characteristics and outcome data. Using Risser staging observations, pelvic maturity age was set at 16, and accordingly, the women were divided into two groups (younger vs. older teens). Analysis was performed using Fisher's exact, student t test, and logistic regression modeling.

RESULTS

Older teen mothers (16-18 years, n = 609) had higher rates of malposition (22 vs. 12 %, p = 0.02) when compared with younger teens (≤15 years, n = 98). Among all women with a malpositioned fetus, older teens had a higher body mass index (BMI: 32.6 ± 6.7 vs. 28.5 ± 3.5, p = 0.04) and subsequent need for cesarean delivery (69 vs. 33 %, p = 0.02) when compared with their younger counterparts. Although younger teens were more successful in having a vaginal delivery (67 %) with an OP/OT position, it was at the expense of a 25 % rate of severe perineal laceration (third/fourth degree).

CONCLUSION

Obesity, and not young maternal age or pelvic immaturity, is associated with fetal malposition. The direct association with increasing pre-pregnancy BMI and the long-term impacts of the high rates of cesarean delivery in this young population underscores the need for more public health focus.

The association between persistent occiput posterior position and neonatal outcomes

OBJECTIVE

To examine the effect of persistent occiput posterior position on neonatal outcome.

METHODS

This is a retrospective cohort study of 31,392 term, cephalic, singleton births. Women with neonates born in persistent occiput posterior position at delivery were compared to those with occiput anterior position. Women with occiput transverse position were excluded. The association between occiput posterior position and neonatal outcomes, including 5-minute Apgar scores, umbilical cord gases, meconium-stained amniotic fluid, meconium aspiration syndrome, birth trauma, admission to the intensive care nursery, and length of stay were examined using chi(2) and Student t tests. Potential confounders (maternal age, ethnicity, parity, gestational age, epidural anesthesia, labor induction, length of labor, meconium, chorioamnionitis, birth weight, and year of delivery) were controlled for by using multivariable logistic regression and linear regression analyses.

RESULTS

There were 2,591 (8.2%) neonates delivered in occiput posterior position of the total cohort of 31,392 deliveries. Compared with occiput anterior, neonates delivered in occiput posterior position had higher risks for adverse outcomes, including 5-minute Apgar score less than 7 (odds ratio [OR] 1.50, 95% confidence interval [CI] 1.17-1.91), acidemic umbilical cord gases (OR 2.05, 95% CI 1.52-2.77), meconium-stained amniotic fluid (OR 1.29, 95% CI 1.17-1.42), birth trauma (OR 1.77, 95% CI 1.22-2.57), admission to the intensive care nursery (OR 1.57, 95% CI 1.28-1.92), and longer neonatal stay in the hospital (OR 2.69, 95% CI 2.22-3.25).

CONCLUSION

Persistent occiput posterior position at delivery is associated with higher risks of adverse neonatal outcomes compared with neonates delivered in the occiput anterior position. This information may be important in counseling women who experience persistent occiput posterior position in labor.

LEVEL OF EVIDENCE

II-2.

Is epidural analgesia a risk factor for occiput posterior or transverse positions during labour?

OBJECTIVE

The aim of this study was to assess whether the station of the fetal head at epidural placement is associated with the risk of malposition during labour.

STUDY DESIGN

Retrospective study (covering a 3-month period) of patients in labour with singleton cephalic term fetuses and epidural placement before 5 cm of dilatation. We studied the following risk factors for malposition: station and cervical dilatation at epidural placement, induction of labour, parity and macrosomia. Malposition, defined as all occiput posterior and occiput transverse positions, was assessed at 5 cm of dilatation because of our policy of systematic manual rotation for malpositions.

RESULTS

The study included 398 patients, 200 of whom had malpositions diagnosed at 5 cm of dilatation. In both the univariate and multivariate analyses, station at epidural placement was the only risk factor significantly associated with this malposition (adjusted OR: 2.49, 95% CI 1.47-4.24). None of the other factors studied was significantly associated with malposition: nulliparity (OR 1.45, 95% CI 0.96-2.20), macrosomia (OR 0.75, 95% CI 0.37-1.50), induction of labour (OR 0.84, 95% CI 0.49-1.45), or dilatation less than 3 cm at epidural administration (OR 1.16, 95% CI 0.59-2.30). Only three infants of the 365 delivered vaginally (0.8%) were born in occiput posterior positions.

CONCLUSION

Epidural placement when the fetal head is still "high" is associated with an increased rate of occiput posterior and transverse malpositions during labour.

The impact of occiput posterior fetal head position on the risk of anal sphincter injury in forceps-assisted vaginal deliveries

OBJECTIVE

A forceps-assisted vaginal delivery is a well-recognized risk factor for anal sphincter injury. Some studies have shown that occiput posterior (OP) fetal head position is also associated with an increased risk for third- or fourth-degree lacerations. The objective of this study was to assess whether OP position confers an incrementally increased risk for anal sphincter injury above that present with forceps deliveries.

STUDY DESIGN

This was a retrospective cohort study of 588 singleton, cephalic, forceps-assisted vaginal deliveries performed at our institution between January 1996 and October 2003. Maternal demographics, labor and delivery characteristics, and neonatal factors were examined. Statistical analysis consisted of univariate statistics, Student t test, chi2, and logistic regression.

RESULTS

The prevalence of occiput anterior (OA) and OP positions was 88.4% and 11.6%, respectively. The groups were similar in age, marital status, body mass index, use of epidural, frequency of inductions, episiotomies, and shoulder dystocias. The OA group had a higher frequency of rotational forceps (16.2% vs 5.9%, P = .03), greater birth weights (3304 +/- 526 g vs 3092 +/- 777 g, P = .004), and a larger percentage of white women (48.8% vs 34.3%, P = .04). Overall, 35% of forceps deliveries resulted in a third- or fourth-degree laceration. Anal sphincter injury occurred significantly more often in the OP group compared with the OA group (51.5% vs 32.9%, P = .003), giving an odds ratio of 2.2 (CI: 1.3-3.6). In a logistic regression model that controlled for occiput posterior position, maternal body mass index, race, length of second stage, episiotomy, birth weight, and rotational forceps, OP head position was 3.1 (CI: 1.6-6.2) times more likely to be associated with anal sphincter injury than OA head position.

CONCLUSION

Forceps-assisted vaginal deliveries have been associated with a greater risk for anal sphincter injury. Within this population of forceps deliveries, an OP position further increases the risk of third- or fourth-degree lacerations when compared with an OA position.

Ultrasonographic occiput position in early labour in the prediction of caesarean section

OBJECTIVE

To investigate the value of ultrasonographically determined occiput position in the early stages of the active phase of labour, in addition to traditional maternal, fetal and labour-related characteristics, in the prediction of the likelihood of caesarean section.

DESIGN

Prospective observational study.

SETTING

District general hospital in the UK.

POPULATION

Six hundred and one singleton pregnancies with cephalic presentation in active labour at term with cervical dilatation of 3-5 cm.

METHODS

Transabdominal sonography to determine fetal occiput position was carried out by an appropriately trained sonographer immediately before or after the routine clinical examination by the attending midwife or obstetrician.

MAIN OUTCOME MEASURE

Caesarean section.

RESULTS

Delivery was vaginal in 514 (86%) cases and by caesarean section in 87 (14%). The fetal occiput position was posterior in 209 (35%) cases and in this group the incidence of caesarean section was 19% (40 cases), compared with 11% (47 of 392) in the non-occiput posterior group. Multiple regression analysis revealed that significant independent contribution in the prediction of caesarean section was provided by maternal age (OR 1.1, 95% CI 1.0-1.2), Afro-Caribbean origin (OR 2.4, 95% CI 1.2-4.6), height (OR 0.93, 95% CI 0.89-0.97), parity (OR 0.2, 95% CI 0.1-0.4), type of labour (OR 2.2, 95% CI 1.3-3.8), gestation (OR 1.4, 95% CI 1.1-1.7), fetal head descent (OR 0.6, 95% CI 0.4-0.9), occiput posterior position (OR 2.2, 95% CI 1.3-3.7) and male gender (OR 2.0, 95% CI 1.2-3.5).

CONCLUSIONS

The risk of caesarean section can be estimated during the early stage of active labour by the sonographically determined occiput position, in addition to traditional maternal, fetal and labour-related characteristics.

MR imaging pelvimetry: a useful adjunct in the treatment of women at risk for dystocia?

OBJECTIVE

The objective of this study was to test the clinical value of MR imaging for diagnosing cephalopelvic disproportion and for predicting labor outcome in women at risk for dystocia.

SUBJECTS AND METHODS

Antepartum fetal sonography and maternal MR imaging pelvimetry measurements were performed at term in 38 pregnant women at risk for dystocia with a single fetus in cephalic presentation. Various methods used to diagnose cephalopelvic disproportion were evaluated in a blinded manner for their accuracy to predict both the presence of cephalopelvic disproportion and the mode of delivery (vaginal vs cesarean).

RESULTS

None of the methods tested yielded both high sensitivity (15-100%) and high specificity (24-92%) for determining the presence of cephalopelvic disproportion and high levels of accuracy for predicting labor outcome (overall predictability, 50-74%).

CONCLUSION

To achieve increased reliability of MR imaging pelvimetry in the diagnosis and treatment of dystocia and in predicting labor outcome, new methods assessing fetal-pelvic compatibility, including measurements of the pelvic outlet and the shape and configuration of the pelvis, need to be established and prospectively tested before firm recommendations for clinical use can be made.

Anesthesia and the progress of labour

CONCLUSIONS

The last decade has seen a remarkable advance in our understanding of the effects of regional analgesia on the progress and outcome of labour. In particular, the appearance of several well conducted prospective, randomized trials have helped confirm the opinion of most anesthesiologists and a growing number of obstetricians, that epidural analgesia only minimally lengthens labour and does not increase the risk of cesarean section. But the extraordinary methodological complexities of studying this unblindable treatment in patients who are anything but ambivalent about whether or not they receive it ensures the debate will continue. It is perhaps time to move away from outcome studies and on to investigations of the putative mechanisms of any effects epidural analgesia may have on the labour and delivery process. It is also vital to place greater emphasis on the interaction between obstetrical practice, analgesic technique, and the patient. There may be important differences between subsets of patients with regard to their risk of cesarean section and the effect epidural analgesia may have on this risk. This is almost certainly true for certain obstetrical practices. Only by an appreciation of the actual physiology of epidural analgesia in the context of obstetrical care and the labour process itself will one of the longest running debates in anesthesiology come to an end.

Labour analgesia. A risk-benefit analysis

The pain associated with labour can be severe. The ideal labour analgesic does not exist and systemic opioids provide little relief. Nausea, vomiting and sedation are common adverse effects of systemic opioids. Paracervical block can relieve only the pain of the first stage of labour. The duration of analgesia obtained using paracervical block is limited and repeat blocks increase the risk of direct fetal injection. Epidural analgesia effectively relieves labour pain. The insertion of an epidural catheter can provide continuous analgesia throughout labour. In addition, the catheter can be used to provide surgical anaesthesia, should operative delivery be required. Epidural local anaesthetics commonly produce maternal hypotension and motor blockade. However, opioids potentiate the effect of epidural local anaesthetics. Thus, concomitant epidural opioid injection allows the use of lower concentrations of local anaesthetics, decreasing the frequency and severity of hypotension and motor blockade. Epidural analgesia has other, potentially catastrophic, adverse effects but, with safe clinical practice, these problems are extremely rare. Intrathecal injection of opioids or local anaesthetics also effective labour analgesia. However, no single intrathecal drug or drug combination reliably provides analgesia for the duration of labour. Many clinicians use both intrathecal and epidural analgesia as a combined spinal-epidural technique. This approach provides the rapid onset of intrathecal drugs and the flexibility of continuous epidural block. Fetal heart rate decelerations occasionally follow the use of any of the above labour analgesic techniques. Most studies of the aetiology of fetal heart rate decelerations have focused on factors unique to each analgesic technique. However, the similar timing and appearance of fetal bradycardia suggests a common cause. Induction of maternal analgesia may transiently alter the balance between factors encouraging and inhibiting uterine contraction. A temporary increase in the uterotonic effects of endogenous or exogenous oxytocin may then produce a tetanic uterine contraction with subsequent decrease fetal oxygen delivery and resultant fetal bradycardia. Regardless of aetiology, these bradycardias are transient and should not produce maternal or fetal morbidity. Much controversy surrounds the effects of analgesia, especially epidural block, on the course and outcome of labour. Various studies have reported that epidural analgesia slows labour, increases the incidence of malposition of the fetal head, increases the need for forceps delivery and increases the risk of caesarean delivery. Most of the studies reporting these effects are retrospective and nonrandomised. More careful studies suggest that specific anaesthetic techniques (i.e. local anaesthetic-opioid mixtures) or obstetrical management can limit or eliminate these 'risks' of epidural labour analgesia.