By the turn of the last century, many obstetric units in the United Kingdom had developed guidelines to deal with emergency situations occurring on the labor ward. These guidelines, which are generally based on those developed by professional bodies,1–4 usually include strategies for managing women at increased risk of shoulder dystocia and describe protocols for overcoming the obstruction when it occurs.
By the late 1990s, the McRoberts’ maneuver,5 described as a simple and effective procedure for overcoming shoulder dystocia, had become widely known in the United Kingdom, and the technique was being adopted in many obstetric units and included in labor ward guidelines as one of the first procedures to be used. By 2001, regular training sessions for labor ward staff on the management of shoulder dystocia were being conducted in our obstetric unit, as in many other units.
By 2004, the routine monthly performance indicators of problem deliveries in the unit indicated that there seemed to be an increasing number of cases of shoulder dystocia and possibly also brachial plexus injuries, and this prompted the present study. The objective was to investigate trends in shoulder dystocia prevalence, associated maternal, fetal and neonatal morbidity and relate these trends to any changes in the methods used to overcome shoulder dystocia.
MATERIALS AND METHODS
Cases of shoulder dystocia during the 15-year period January 1991 to December 2005 inclusive were identified through the obstetric maternity computer data system,6 which is subject to continuous stringent quality control, using International Classification of Diseases codes 660.400 and 0660\10. Individual clinical case records were examined to confirm authenticity and collect details on patient management and morbidity; “shoulder dystocia” had to be documented in the records for the case to be included. In addition, all cases of brachial plexus injury, diagnosed during the neonatal period, were separately identified through International Classification of Diseases codes P140\10, 141\10 or 143\10, and 767.600 using the same system, and authenticity was confirmed; cases were not assessed to determine if the palsy had persisted at 1 year of age. The demographic and delivery statistics for all vaginal deliveries in the unit for each of the years studied were also obtained.
As well as demographic data and routine labor and neonatal outcome variables, information on delivery management once shoulder dystocia had been diagnosed was specifically recorded as well as the time interval between the delivery of the fetal head and the trunk, when this was documented. The grade of the clinician managing the delivery was noted, identifying senior obstetricians with at least 3 years higher training in the specialty, including those of consultant status.
The condition of the neonate at birth was recorded and included 1- and 5-minute Apgar scores and cord arterial and venous pH and base excess values. A diagnosis of acidosis was made if the cord arterial pH was 7.10 or less and the base excess less than –12.0 mmol/L7; if cord gases had not been measured, neonates with a 1-minute Apgar score of 3 or less were included. Neonatal morbidity, identified before hospital discharge, included evidence of brachial plexus injury however transient, all fractures involving the upper limbs or ribs, and significant hypoxia, including cardiac arrest at birth, 5-minute Apgar scores of 3 or less,8 or hypoxic ischemic encephalopathy diagnosed during the neonatal period. 4Child,9,10 a regional database registering children with cerebral palsy, vision loss, and hearing loss was interrogated for the purpose of linking subsequent morbidity.
The occurrence of maternal injury was documented, with particular emphasis on perineal trauma and complications of the third stage of labor, with the management provided. All pregnancies subsequent to the index pregnancy were identified when managed in the same unit; information relating to the gestation and management of these subsequent deliveries, including recurrent shoulder dystocia and birth weight, was also recorded.
Statistical analyses included calculation of relative risk, together with 95% confidence intervals, χ2 test, Fisher exact test, or unpaired two-sample t test as appropriate. Linear regression analyses were carried out to test for changes in incidence over time.
There were 95,321 mothers during the study period delivering 96,978 newborns; 79,781 of these were vaginal deliveries, and thus the fetus was at risk of classical shoulder dystocia. Figure 1 illustrates the annual numbers of vaginal deliveries. Total deliveries decreased each year, as did vaginal deliveries. The mean annual percentage of vaginal deliveries was 82.5% (95% confidence interval [CI] 80.8–84.3%) decreasing by 0.64% each year (P<.001). The proportion of women undergoing labor induction was around 26% per year with very little variation over the 15 years (P=.81). There was a significant increase of 0.82% per year (95% CI 0.56 to 1.09, P<.001) in the use of epidural analgesia for pain relief during labor, averaging 28.3% annually.
There were slight reductions over the 15-year period in the lengths of both the first and second stages of labor for both nulliparas and multiparas. There was a significant reduction in the proportion of nulliparas with a first stage of labor lasting longer than 12 hours, averaging 3.5% over the fifteen years (decrease 0.09% per year, P=.005) and in the proportion of multiparas with a first stage of labor longer than 8 hours, average 3.2% (decrease 0.55% per year, P=.06). Fewer than 4% of vaginal deliveries had a prolonged second stage labor (more than 4 hours for nulliparas and more than 2 hours for multiparas), with no significant changes over time. Vaginal deliveries assisted by forceps or ventouse remained unaltered during the 15 years at 17% (95% CI 16.0–17.8%), and the proportion of neonates born with a birth weight of 4.0 kg or more remained unchanged at 11.7% (95% CI 11.2–12.1%) as did the proportion with a birth weight of 4.5 kg or more at 1.6% (95% CI 1.5–1.7%). A total of 2,558 neonates (3.2%, 95% CI 3.0–3.4%) were acidotic at birth, with a slight decrease of 0.06% per year (P=.02).
There were 514 cases of shoulder dystocia during the 15 years, confirmed by a thorough examination of the clinical delivery details, giving an overall rate of 0.64% of vaginal deliveries (1:155 proportion of vaginal deliveries). There were 25 (4.6%) cases distributed throughout the study period where shoulder dystocia was identified by coding but could not be confirmed by a thorough examination of the clinical delivery notes, and these cases were eliminated from further analysis. Figure 1 illustrates the annual number of vaginal deliveries and cases of shoulder dystocia; these included three cases of antepartum intrauterine fetal death. Figure 2 shows the annual rates of shoulder dystocia per 1,000 vaginal deliveries (95% CI 5.1–7.8%). There was a significant linear trend (P=.03) increasing by 0.292 per 1,000 vaginal births or approximately 3 per 10,000 births extra each year. Table 1 identifies the characteristics of all women delivering vaginally, together with the 514 complicated by shoulder dystocia. Of the features associated with an increased risk of shoulder dystocia in previous studies, all were confirmed except labor induction and the use of intrapartum epidural analgesia.
Of the 514 dystocia cases, 264 (51%) were managed by midwives alone, 66 (13%) by an obstetrician assisting a midwife, and 183 (36%) by an obstetrician conducting an instrumental delivery; there was a slight increase in obstetrician involvement of 1.5% per year (P=.033). The proportion of cases with consultant obstetric involvement increased from 5 of 169 (3%) during the first 5 years to 12 of 209 (6%) during the last 5 years. Table 2 lists the procedures used and the order in which they were used when more than one maneuver was used to overcome the obstruction; the fetal head–trunk delivery interval was recorded in 293 (57%) cases and these have also been analyzed in the table. There was a significant increase in birth weight with the need for additional procedures to complete the delivery (average 73 g increase per procedure; 95% CI 28.6–117.8 g, P=.001). The McRoberts’ maneuver was used at some stage in the management of 270 deliveries; it was used for 5 of 163 (3%) cases during 1991 to 1995, 72 of 140 (51%) cases during 1996 to 2000, and 193 of 211 (91%) cases during 2001 to 2005, an obvious increase over time (P<.001). When it was the first procedure used to overcome the obstruction, it was successful in 105 of 231 (45%) cases.
Seventy-five (14%) women sustained a primary postpartum hemorrhage, 67% of whom underwent an instrumental delivery, and the same proportion delivered using an episiotomy; the frequency of primary postpartum hemorrhage did not change over time. An episiotomy was made for 282 (55%) deliveries with no information available for one delivery. There was a decrease in episiotomies of 3.8% per year during the study period (2.0%, 95% CI 5–6%, P=.001) but no change in the numbers of women with intact perineum (P=.9). Third- or fourth-degree tears were sustained in 29 (6%) cases, 13 with an episiotomy and 16 without an episiotomy (P=.26). Seventeen cases occurred after 182 (9%) instrumental deliveries, and 12 occurred after 328 (4%) spontaneous deliveries (P=.009). The perineum remained intact in 74 of the 231 (32%) cases where an episiotomy had not been made. Five women had perineal complications: three had a vulvovaginal hematoma, one had a vulval infection, and one required perineal resuturing.
Fifty-nine of 514 (11%) neonates experienced serious neonatal morbidity after shoulder dystocia, and one neonate suffered a brachial plexus injury after delivery by cesarean. Brachial plexus injury was diagnosed in 44 (8.3%) (1:1821 vaginal deliveries and 1:12 cases of shoulder dystocia), 11 neonates suffered a fracture, and eight required cardiac massage at delivery or developed hypoxic ischemic encephalopathy. Neonates experiencing severe hypoxia did not have any other injuries, whereas four with a brachial plexus injury also suffered a fracture. Serious neonatal morbidity occurred in 35 among 270 (13%) neonates delivered using the McRoberts’ maneuver compared with 24 among 245 (10%) delivered without the McRoberts’ maneuver experienced serious neonatal morbidity (P=.27). Table 2 lists the frequency of brachial plexus injury and acidosis at delivery according to the number of procedures needed to overcome the obstruction to delivery.
Of the 44 brachial plexus injuries, 43 were Erb’s palsy and one Klumpke’s palsy. Three neonates suffered a transient facial palsy, one of whom also had an Erb’s palsy. As shown in Figure 2, the rate of brachial plexus injury rose over time, increasing at a rate of 0.06 per 1,000 vaginal births per year (P=.007). The rate of brachial plexus injury to neonates with shoulder dystocia increased over time by 0.41% per year (P=.027). Nineteen (43%) of the 44 cases occurred after a spontaneous delivery, with obstetric assistance required for eight (42%) of them. The remaining 25 cases were instrumental deliveries managed by senior obstetricians, of which three were by consultants (Table 3). The McRoberts’ maneuver was not used for the delivery for any of the 11 cases (0%) delivered during 1991–1995, eight of 13 cases (61%) during 1996–2000 and 19 of 20 cases (95%) during 2001–2005; the case record for one case delivered in 1993 was not available for examination. Of the fractures, five were clavicular (two of whom had an Erb’s palsy), five humeral (two of whom had an Erb’s palsy), and one experienced a rib fracture. In eight of these cases, the McRoberts’ maneuver was used, in two it was not, and for one case the case records were not available. In four of the five cases of humeral fracture, the posterior arm was manipulated to overcome the obstruction, and an episiotomy was made in three of these four cases.
Thirty-six (7%) neonates showed evidence of acidosis at delivery: 28 had acidotic cord gases, and 8, without paired cord blood gas measurements, had a 1-minute Apgar score of 3 or less. Five of these 36 required external cardiac massage, and four developed hypoxic ischemic encephalopathy. Two neonates, one delivered in 1993 and the other in 2003, developed cerebral palsy and died in early childhood. Three of the acidotic neonates also suffered a brachial plexus injury. The McRoberts’ maneuver was used to overcome shoulder dystocia in 18 (45%) of these 36 cases; in five cases, no specific procedures were used, and none sustained a brachial plexus injury, but one neonate required external cardiac massage. Twenty-seven of these 36 (68%) weighed 4.0 kg or more and 13 (33%) weighed 4.5 kg or more. In 26 instances, the head–trunk interval was recorded, and the median interval was 5 minutes, ranging between 1 and 14 minutes; in 15 (60%), the interval was 4 minutes or longer. The median interval was 3 minutes 30 seconds (range 1–6 minutes) for the 22 delivered with the assistance of an episiotomy compared with 6 minutes (range 1–10 minutes) for the seven without the aid of an episiotomy (P=.21). The head–body interval for the two neonates that died in infancy was 5 and 7 minutes, respectively. Interrogation of the 4Child database of children with impairment did not identify any additional cases of impairment.
One hundred twenty-six women have had at least one subsequent delivery, and Figure 3 illustrates the relationship between the index and subsequent birth weight; 32% neonates weighed more than the indexed neonate. Thirty-six (29%) subsequent deliveries were managed by antepartum cesarean delivery, and 12 (33%) of these neonates were heavier than the index neonate. Of the 90 who labored, 32 (35%) had labor induced, 15 before 40 weeks of gestation, with 29 delivering vaginally, and 60 (65%) spontaneously labored, with 58 delivering vaginally. Six (20%) of the neonates delivered after labor induction and 23 (40%) of the neonates delivered after spontaneous labor onset were heavier than the previous siblings. Five women who labored were delivered by intrapartum cesarean and two (20%) of these neonates were heavier than the index neonate.
Nine of the 87 (10%) women who delivered vaginally a second time had repeat shoulder dystocia and thus appear twice in the original database; in eight cases this occurred with the next confinement, and in one instance it occurred during the third confinement after the index delivery. Six of the cases occurred after spontaneous labor onset, five occurred during an instrumental delivery, and the birth weight of each of these neonates was heavier than the index pregnancy birth weight, except for the case that occurred after two interim trouble-free deliveries. Of the nine women whose previous neonates had sustained a brachial plexus injury and who have delivered another neonate, seven were delivered by planned antepartum cesarean, and two delivered vaginally; both of these latter two neonates were larger than the index neonate, and shoulder dystocia occurred again with one neonate experiencing a transient brachial plexus injury similar to his sibling.
The overall rate of shoulder dystocia in our study was 0.6%, which is comparable to the rate reported in other studies also involving relatively large numbers.11–14 However, we observed a significant increasing trend at the rate of 0.03% per year during the study period. The characteristics of the cases of shoulder dystocia were consistent with those reported in many other previous studies (increased frequencies in multiparas, prolonged first or second stages of labor, after instrumental vaginal deliveries, high birth weight neonates, and women with high BMI)15–19 The distribution of birth weight for the population studied with 11% neonates weighing 4.0 kg or more is the same as that reported by a national survey conducted in the United Kingdom during 2000–2001.20 There was, however, no increase in the rates of these risk characteristics in the base population during the study period, which leads us to conclude that the increased rate of shoulder dystocia is possibly the result of an increase in diagnosis due to an increased awareness, stimulated by the training workshops for dealing with shoulder dystocia. An increase in rate from 0.2% in 1979 to 2.1% in 2003, or 1:200 to 1:50 vaginal deliveries, was noted in Maryland.21 Despite our tentative explanation, there was a significant increase in the rate of brachial plexus injuries over the same period from 1:20 to 1:10 cases of shoulder dystocia. Two studies from the West Midlands in the United Kingdom have suggested an increase in the rate of brachial plexus injury after shoulder dystocia from 1:77 in the early 1990s to 1:4 in 2003.22,23
The ways in which shoulder dystocia was managed changed considerably during the study period with use of the McRoberts’ maneuver, which was rarely used during the first 5 years, increasing to 91% of cases during the last 5 years. A 46% successful outcome when the McRoberts’ maneuver was used as the first procedure is similar to the 40% and 42% reported by others.24,25 Its use, therefore, does not guarantee a successful outcome, and this should be acknowledged by those expressing opinions in medico–legal matters.26 The finding of a significant direct association between fetal weight and the need for additional procedures to complete the delivery has also been observed by others.22 What was surprising, however, was the lack of effect on the rate of brachial plexus injuries, with 19 of the 20 cases of brachial plexus injury encountered since 2001 being managed with the McRoberts’ maneuver, compared with only eight of 13 before 2001. Thus, despite the dramatic increased use of the McRoberts’ maneuver, the incidence of brachial plexus injury has not fallen. Although it might be argued that this lack of decrease was because the maneuver was not correctly applied, the rates of brachial plexus injuries after all vaginal deliveries (1:1803) and after shoulder dystocia (1:12) in our study are no higher than the range 1:448–1,708 for all deliveries and 1:4–12 for vaginal deliveries reported in many studies involving large patient numbers in recent years.24,25,27–29 This increase is even more surprising considering the 50% increase in cesarean deliveries during the study period from 12% in 1991 to 21% in 2005 and the unchanging birth weight statistics over the same period. The report published in 1998 examining the incidence and causes of brachial plexus injuries in the United Kingdom and Northern Ireland17 concluded that there had been no significant change in the incidence of brachial plexus palsy over the preceding 40 years, although the methods used to overcome shoulder dystocia were not investigated in that study. Analyses of results published by different units to examine possible trends over different time periods may not provide sufficiently reliable data from which to draw conclusions, but our study has shown that the introduction of the McRoberts’ maneuver has not improved the chance of overcoming shoulder dystocia or reduced the risks of brachial plexus injury.
As many previous studies have shown, there is an increased risk of significant maternal trauma with shoulder dystocia, with a twofold to threefold increase in primary postpartum hemorrhage similar to that reported by others.24,30 The rate of third- and fourth-degree perineal tears at 7% is approximately double that commonly reported for all vaginal deliveries,31,32 and although these tears occurred more commonly when an episiotomy had not been made, the results do not support the minority view that an episiotomy should invariably be made to overcome shoulder dystocia. In addition, an episiotomy did not reduce neonatal morbidity or shorten head–body intervals.
Acidosis accompanied 7% of deliveries, and 1.5% neonates experienced some hypoxic consequences. The frequency with which hypoxia occurs during deliveries complicated by shoulder dystocia has not been thoroughly addressed in the literature. However, although considered by Nesbitt et al,33 who observed an increase in asphyxiated neonates born after shoulder dystocia compared with the general population, a definition for asphyxia was not provided. We are not aware of any previous studies that have attempted to follow up neonates born after shoulder dystocia and address the potential long-term effect of the hypoxia that many neonates experience during delivery. There were only two cases in our study where permanent cerebral damage was detected, and both neonates died in early childhood. We recognize that the three neonates born during 2004 to 2005 with hypoxic ischemic encephalopathy during the neonatal period could yet appear on the 4Child register, because cerebral palsy is diagnosed over time, and the ascertainment process continues until the age of 5 years. The mortality rate we have observed is, however. broadly consistent with that reported following the Confidential Enquiry into Stillbirths and Deaths in Infancy in England, Wales and Northern Ireland34; in that analysis, there were 56 deaths among 1,367,851 births (1:24,000 births), compared with the two deaths among 95,321 births (1:47,000 births) in our study. The Confidential Enquiry into Stillbirths and Deaths in Infancy study found that the head–body interval was less than 5 minutes in just under one half of the deaths and less than 10 minutes in 80%. The two fatalities in our study are compatible with the Confidential Enquiry into Stillbirths and Deaths in Infancy observations. The clinician has to balance delivery avoiding mechanical trauma with speed to reduce the risk of hypoxic damage. That only three of the 44 neonates with a brachial plexus injury were acidotic at birth suggests that mechanical injuries can occur early during delivery complicated by shoulder dystocia.
The strategy for managing the next delivery after shoulder dystocia is debated. A cautious approach, planning delivery before the due date, is often adopted as with the 61% antepartum cesarean delivery or labor inductions in our study. Whether this approach is justified has been challenged.35,36 It is of note, however, that approximately one third of neonates delivered subsequent to the shoulder dystocia were heavier, a proportion that hardly varied between the timed deliveries and those after planned spontaneous onset labor. The 11% recurrence rate of shoulder dystocia in those who subsequently labored and delivered vaginally is similar to the 10–16% reported by other groups,37–39 although it is much greater than the 1% among 93 subsequent vaginal deliveries reported by Baskett and Allen,27 who observed 41% of neonates were heavier than the previous neonate delivered with shoulder dystocia. As anticipated, in virtually all cases of repeat shoulder dystocia in our study, the second neonate was heavier than the first and it is frustrating to acknowledge that there are still no reliable predictors for calculating birth weight using clinical assessment or ultrasound biometry.40–42 In these circumstances, it is difficult to argue against adopting a conservative approach and encouraging future deliveries by cesarean while cautioning against the risk of recurrent shoulder dystocia with another labor and vaginal delivery.
Our results show that despite an increase in cesarean deliveries, there was an increase in the rates of shoulder dystocia and brachial plexus injuries, the latter occurring despite the almost universal adoption of the McRoberts’ maneuver during the last 5 years of the study. Although most of the literature relating to shoulder dystocia has concentrated on preventing injuries to the brachial plexus, the threat of hypoxia deserves greater attention, together with further research into its potential long-term consequences. The increasing rates of both shoulder dystocia and brachial plexus injuries are difficult to explain but are a concern. Although factors associated with an increased risk of shoulder dystocia are well recognized, our ability to predict these cases remains limited, as do reliable predictions of fetal weight.
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