Shoulder dystocia, a complication occurring in approximately 0.5–1.5% of vaginal births, is usually resolved promptly with specialized delivery maneuvers and generally results in no permanent adverse neonatal sequelae. On occasion, shoulder dystocia will be unresponsive to the recommended techniques and a prolonged interval from delivery of the head to delivery of the body will result in neonatal depression, hypoxic ischemic encephalopathy, or even neonatal death.
It has generally been assumed that the longer the head-to-body delivery interval, the greater the chance of neonatal depression. However, the exact relationship between this time interval and neonatal depression has never been delineated explicitly. If a clinician could know at what point during a shoulder dystocia delivery the risk of depression becomes significant, this knowledge could help guide the tempo of delivery efforts.
The literature evaluating the relationship between head-to-body delivery interval and neonatal depression is contradictory. Several small studies with fewer than 45 neonates, such as Stallings et al1 and Heazell et al,2 have reported no statistical correlation between head-to-body delivery interval and umbilical artery base deficit or pH. However, both of these studies had so few examples with prolonged delivery interval that the results were bound to be statistically insignificant. In contrast, the similarly sized study by Allen et al3—36 neonates with shoulder dystocia complicated by persistent brachial plexus injury—did demonstrate evidence of an adverse effect of increasing head-to-body delivery intervals on 5-minute Apgar scores. They found that the mean head-to-body delivery interval in neonates with 5-minute Apgar scores 6 and higher was 4.9 plus or minus 1.1 minutes. This was significantly longer than the mean head-to-body delivery interval of 2.5 plus or minus 1.4 minutes seen in neonates with Apgar scores of 7 or above. None of these neonates with persistent brachial plexus injury experienced permanent asphyxia-related complications.
Leung et al's large study4 with 200 participants did find a statistically significant, albeit small, correlation between head-to-body delivery interval and umbilical artery pH (r=−0.210, P=.003) and umbilical artery base excess (r=−0.144, P=.045). If the head-body delivery interval was less than 5 minutes, the risk of severe acidosis—pH less than 7.0—was 0.5%, whereas this risk was 5.9% when the delivery interval was 5 minutes or greater. Interestingly, the largest study on fatal shoulder dystocia—the 1998 Confidential Enquiry into Stillbirths and Deaths in Infancy5—found that a delivery interval less than 5 minutes was not protective of perinatal death. In that study, 47% of 45 fatal cases had a head-to-body delivery interval less than 5 minutes. In 20% the interval was more than 10 minutes.
In the present report we sought to evaluate the relationship between head-body delivery interval and fetal depression in two groups of shoulder dystocia deliveries: those that were uncomplicated and those that were associated with persistent brachial plexus injury.
MATERIALS AND METHODS
All in this study were singleton, cephalic-presenting neonates at 36 or more weeks of gestation who had experienced shoulder dystocia delivery and for whom the head-to-body delivery interval had been recorded. This study protocol received Institutional Review Board clearance from the Human Research Investigations Committee of the Newton-Wellesley Hospital in Newton, Massachusetts.
The data from the 55 neonates with persistent brachial plexus injury associated with shoulder dystocia were drawn from the cumulative medical–legal experience of one author (H.M.L.) spanning the years 1995–2010. All brachial plexus injuries had persisted for several years at the time of litigation. The 55 neonates were further divided into two groups: 14 with and 41 without evidence of central nervous system depression at birth. Neonatal depression was defined by the presence of any of the following: fetal demise, cardiopulmonary resuscitation or intubation in the delivery room, an umbilical artery pH less than 7.00, or a 5-minute Apgar score of 5 or less. Umbilical artery gases were available in less than half of the depressed neonates. The other three markers were chosen because they were objective and because they had been consistently recorded in the medical records.
The uncomplicated shoulder dystocia group comprised 127 neonates delivered at the Newton-Wellesley Hospital, a university-affiliated community hospital in suburban Boston, between January 1, 1999, and December 31, 2008. Instances of shoulder dystocia were identified through medical record coding and verified via chart review based on the American College of Obstetricians and Gynecologists definition of shoulder dystocia: a delivery that requires additional obstetric maneuvers following failure of gentle downward traction on the fetal head to effect delivery of the shoulders.6 Shoulder dystocia cases were excluded if there were fractures, brachial plexus injury, or any of the depression criteria listed above. Head-body delivery intervals were taken from the medical record with the precision that was available. It would appear from the records that time intervals were often estimated from standard clocks or fetal monitor strip notations or by special timers activated when the shoulder dystocia began.
Statistical evaluations utilized one-way analysis of variance testing for the differences between medians with Bonferroni multiple comparison posttests and χ2 or Fisher exact tests for proportions where appropriate. Statistical analyses were performed using GraphPad Prism 5.03 for Windows.
Maternal and delivery characteristics of the three groups are outlined in Table 1. The median head-to-body delivery interval rose progressively across the groups, with the lowest value in the uncomplicated shoulder dystocia births and the highest in births with both persistent brachial plexus injury and depression. It was noted that women with complicated shoulder dystocia had higher body mass indexes (calculated as weight (kg)/[height (m)]2) and larger neonates; this correlation has been reported frequently in the past.6
In the uncomplicated shoulder dystocia group, the median head-body delivery interval was 1.0 minutes with an interquartile range of 0.5–1.0. The median for neonates with persistent brachial plexus injury and no depression was 2.0 minutes (interquartile range 1.0–4.0); for neonates with both persistent brachial plexus injury and neonatal depression, the median was significantly longer at 5.3 minutes (interquartile range 3.9–13.3; P<.001). Interquartile range is the range between the 25th and 75th percentile values and is used to indicate the spread of data in a group that is not normally distributed.
The actual distributions of head-to-body delivery intervals, displayed in Figure 1, show the relatively narrow range of intervals for the uncomplicated shoulder dystocia group with nearly three quarters of them delivering within 1 minute. In contrast, those with persistent brachial plexus injury and depression spanned a much larger range of 1 to 25 minutes.
To better display the percentage of neonates born by any particular time interval, the cumulative percentages are displayed in Figure 2. By 3 minutes, 98% of the neonates in the uncomplicated shoulder dystocia group had been born and by 4 minutes all such neonates were born. In the injury with depression group, a sharp rise was seen between 3 and 4 minutes. Neonates with persistent brachial plexus injury without depression showed a fairly steady increase, with each of the first 3-minute intervals and then a gradual tapering so that 98% had occurred by a delivery interval of 6 minutes and 100% at 8 minutes.
The percentages of neonates falling above or below selected delivery interval cutoffs are shown in Table 2. An ideal delivery interval cutoff would be one under which all of the uncomplicated neonates are found and over which all the neonates with depression are found. No such demarcation was seen to exist. For example, all of the uncomplicated shoulder dystocia deliveries had occurred by 4 minutes—but so had a substantial portion of those with isolated persistent brachial plexus injury (85.4%) as well as 42.9% of neonates with injury and depression. This of course means that 57% of the neonates with injury and depression and 15% the group of injury without depression had delivery interval over the 4-minute mark.
By design, the uncomplicated shoulder dystocia group excluded neonates with any notation of arm weakness or limitation of movement. All of these excluded neonates had 5-minute Apgar scores of 6 or more and all delivered within 3 minutes or less, with a median delivery interval of 1.5 minutes. They thus would contribute little additional information on the relationship between prolonged delivery interval and neonatal depression. In addition, their exclusion kept the control group homogenous, thus making it easier to generalize their results to other similar groups in the future.
This study has measured head-to-body delivery intervals in uncomplicated shoulder dystocia deliveries and in shoulder dystocia deliveries resulting in persistent brachial plexus injury with and without immediate neonatal depression. A positive relationship was observed between increasing length of delivery interval and neonatal depression at birth. All the births in the uncomplicated shoulder dystocia group were resolved within 4 minutes or less and most within 1 minute. The percentage of neonates with depression rose sharply after 3 minutes. This is consistent with the observations of Spong et al7 and Beall et al.8
Of interest, even the shortest delivery intervals included some neonates with depression. This should not be unexpected because some neonates would have entered the final stages of delivery with decreased fetal reserve. As we were unable to access most of the electric fetal monitoring strips from the cases herein reported, we are unable to comment on the condition of the neonates just before their shoulder dystocia deliveries.
Although the two major end points of ultimate clinical significance in shoulder dystocia deliveries are persistent brachial plexus injury and permanent brain damage, this latter complication occurs so rarely that it is practically impossible to study. As an alternative approach, much can be learned by evaluating more common “near misses” such as neonatal depression. This is the approach taken in this report. Clearly, neonatal depression, as defined here, does not equate to long-term neonatal central nervous system injury. But several of the same factors that produce permanent brain injury—hypoxia and acidosis—do occur and can be observed in neonatal depression.
A neonate's ability to tolerate a prolonged head-body delivery interval resulting from a shoulder dystocia delivery has a finite limit, it is impossible to define a completely safe interval. Even studies with fatal shoulder dystocia describe cases covering wide delivery interval ranges, with neonates dying at intervals of 5 and 7 minutes (MacKenzie et al),8 14 minutes (Leung et al),4 and in both “less than 5 minute” and “more than 10 minute” cohorts (Hope et al).5 In contrast, the neonate born after the longest head-body delivery interval in our series—25 minutes—survived.
Yet despite this variation in the ability of some neonates to tolerate prolonged delivery intervals, there is a definite shift to the right of intervals in those neonates born with complications. Whereas almost all neonates experiencing shoulder dystocia without complications delivered by 3 to 4 minutes, the rates of complicated shoulder dystocia deliveries rose substantially after this point.
The major strength of this article lies in the numbers of cases it presents of shoulder dystocia deliveries with resulting persistent brachial plexus injury in which head-to-body delivery intervals have been measured. It is among such deliveries that the excessive time period involved in resolving shoulder dystocias permits one to study the relationship between prolonged delivery interval and neonatal depression. A limitation in this study is the precision of the recorded delivery interval. From the data it appears that clinicians often rounded these times to the nearest half or quarter minute or to 10-second increments. Therefore the cutoffs reported here should be interpreted with this imprecision in mind.
The observations described above have potentially significant clinical implications. This study specifically compares the cumulative rate of births at each head-body delivery time interval for uncomplicated shoulder dystocia births with those of persistent brachial plexus injury with or without neonatal depression. Such information offers guidance to clinicians caught between the admonition to apply only gentle force when using maneuvers to accomplish a shoulder dystocia delivery and the countervailing need to achieve delivery within a critical time frame to prevent hypoxic injury.
1. Stallings SP, Edwards RK, Johnson JWC. Correlation of head-to-body delivery intervals in shoulder dystocia and umbilical artery acidosis. Am J Obstet Gynecol 2001;185:268–74.
2. Heazell AE, Judge JK, Bhatti NR. A retrospective study to determine if umbilical cord pH correlates with duration of delay between delivery of the head and body in shoulder dystocia. J Obstet Gynecol 2004;24:776–7.
3. Allen RH, Rosenbaum TC, Ghidini A, Poggi SH, Spong CY. Correlating head-to- body delivery intervals with neonatal depression in vaginal births that result in permanent brachial plexus injury. Am J Obstet Gynecol 2002;187:839–42.
4. Leung TY, Stuart O, Sahota DS, Suen SS, Lau TK, Lao TT. Head-to-body delivery interval and risk of fetal acidosis and hypoxic ischaemic encephalopathy in shoulder dystocia: a retrospective review. BJOG 2011;118:474–9.
5. Hope P, Breslin S, Lamont L, Lucas A, Martin D, Moore I, et al. Fatal shoulder dystocia: a review of 56 cases reported to the Confidential Enquiry into Stillbirths and Deaths in Infancy. Br J Obstet Gynaecol 1998;105:1256–61.
6. Shoulder dystocia. ACOG Practice Bulletin No. 40 American College of Obstetricians and Gynecologists. Obstet Gynecol 2002;100:1045–50.
7. Spong CY, Beall M, Rodrigues D, Ross MG. An objective definition of shoulder dystocia: prolonged head-to-body delivery intervals and/or the use of ancillary obstetric maneuvers. Obstet Gynecol 1995;86:433–6.
8. Beall MH, Spong C, McKay J, Ross MG. Objective definition of shoulder dystocia: a prospective evaluation. Am J Obstet Gynecol 1998;179:934–7.
9. MacKenzie IZ, Shah M, Lean K, Dutton S, Newdick H, Tucker DE. Management of shoulder dystocia: trends in incidence and maternal and neonatal morbidity. Obstet Gynecol. 2007;110: 1059–68.