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What factors are associated with neonatal injury following shoulder dystocia?

Abstract

Objective:

To identify factors associated with the development of neonatal injury in the setting of shoulder dystocia.

Study design:

Medical record ICD-9 codes and a computerized perinatal database were reviewed to identify cases of shoulder dystocia from January 1996 to January 2001 in a tertiary care center. For confirmation of the diagnosis and collection of data, both maternal and neonatal charts were then reviewed and neonatal injuries categorized as either neurological (brachial plexus injury) or skeletal (clavicular fracture, humeral fracture). Shoulder dystocia cases were divided into groups based on the presence of neonatal injury at delivery or at discharge (with or without Erb's palsy). The group with neonatal injury was compared for demographic and obstetrical factors to the group without injury (control). χ2 test, Mann–Whitney test and logistic regression were used as appropriate.

Results:

During this 5-year period, there were 25 995 deliveries and 206 (0.8%) confirmed cases of shoulder dystocia. Of these cases, 36 (17.5%) had neonatal injury diagnosed at delivery and 25 (12%) remained with significant residual injury at discharge. Of these there were 19 cases of Erb's palsy and six cases of clavicular fracture. No association was found between neonatal injury and maternal age, ethnicity, diabetes, operative vaginal delivery or number of obstetrical maneuvers. However, maternal body mass index >30 kg/m2, a second stage of labor >20 min and a birth weight >4500 g were all associated with an increased risk of neonatal injury at delivery and at discharge, including Erb's palsy. After logistic regression analysis, only a second stage of delivery >20 min remained significantly associated with neonatal injury at discharge.

Conclusion:

In our population, maternal obesity was associated with an increased risk of neonatal injury after shoulder dystocia. In addition, a short second stage of labor (<20 min) was associated with a lower rate of neonatal injury.

Introduction

Shoulder dystocia remains an obstetric emergency with the potential for serious outcomes. It occurs in 0.6–1.4% of all deliveries,1 with possible consequences including neonatal fractures (humeral and clavicular), brachial plexus injury (Erb's or Klumpke's), hypoxic-ischemic encephalopathy, and even neonatal death. Neonatal morbidities in general occur in 21–42% of shoulder dystocia cases, with brachial plexus injury occurring in 8.4–22.7%.2 Clavicular fracture occurs in 5–15% of shoulder dystocia cases;3 however, the majority of these injuries heal well with minimal long-term morbidity. Hypoxic-ischemic encephalopathy and neonatal death are very rare.4

The possibility of neonatal injury is the key reason why shoulder dystocia is of such concern, and there may be certain factors that set cases of shoulder dystocia with injury apart from those without. Although several studies have looked at factors related specifically to brachial plexus injury,5, 6, 7 only one study has examined the injured patients within a shoulder dystocia group to see if any factors set them apart.8 This study, however, was limited in power and was unable to identify any risk factors which predicted brachial plexus injury. Thus, the goal of our study was to examine factors in our population of shoulder dystocia patients in order to determine their association with neonatal injury.

Methods

After approval was obtained from the Human Investigation Committee, medical record ICD-9 codes and a computerized perinatal database were used to identify potential cases of shoulder dystocia that occurred at Hutzel Hospital from January 1996–January 2001. Confirmation of the diagnosis and data were obtained through review of maternal and neonatal hospital charts. Shoulder dystocia was defined as failure of the fetal shoulders to be delivered spontaneously after the head due to impaction of the anterior shoulder against the symphysis pubis, as judged by the clinician delivering the fetus. Inclusion criteria were live born, singleton gestations, in vertex presentation, and the absence of fetal structural or chromosomal anomalies. A prior study using this database has been published.9

Shoulder dystocia cases were divided into two groups based on the presence of neonatal injury. The injury group was then further subdivided into injury at delivery, injury at discharge and type of injury. Neonatal injury information, which was collected by review of neonatal charts, was defined by neonatologists and included both brachial plexus injury (Erb's palsy, Klumpke's palsy) and skeletal injury (clavicular fracture, humeral fracture). Other data collected (from maternal charts) included maternal age, race, maternal body mass index (BMI), pregestational or gestational diabetes, labor induction, oxytocin, epidural anesthesia, operative vaginal delivery (including type and indication), neonatal birth weight and labor characteristics. Precipitous second stage of labor was considered to be <20 min,6 and prolonged second stage was defined as longer than 3 h for nulliparous women with epidural, 2 h of nulliparous without epidural and for parous women with epidural and longer than 1 h for parous women without epidural.

SPSS statistical software package (SPSS Version 10.0, Chicago, IL) was used to compare cases with and without neonatal injury for clinical factors and labor characteristics. Comparisons were performed using the χ2 test with Yates correction and paired Student's t-test, as appropriate. Logistic regression analyses with stepwise regression (P=0.2 used to keep criteria in the model) for all factors associated with neonatal injury were performed. Significance was defined as P<0.05.

Results

During this 5-year study, of 25 995 vaginal deliveries, 206 (0.8%) were complicated by shoulder dystocia that met study criteria. Of these cases, there were 36 neonatal injuries at delivery and 25 (12%) remained at neonatal discharge, including 19 cases of Erb's palsy and six confirmed cases of clavicular fracture. There were no cases of hypoxic-ischemic encephalopathy or neonatal death secondary to shoulder dystocia in our population. Table 1 shows the demographic characteristics of pregnancies, comparing neonates with (1) injury at birth, (2) injury at discharge and (3) Erb's palsy with noninjured neonates. Higher maternal BMI, a maternal BMI 30 kg/m2, greater median length of second stage of labor, and birth weight 4500 g were the factors associated with neonatal injury at birth, neonatal injury at discharge and Erb's palsy. A second stage of labor shorter than 20 min was associated with a lower risk for shoulder-dystocia-related injury. Maternal age, maternal race, maternal height, maternal diabetes, nulliparity, labor induction, operative vaginal delivery and three or more obstetric shoulder dystocia maneuvers were not associated with neonatal injury.

Table 1 Demographics and obstetrical characteristics between injured and noninjured neonates

Stepwise logistic regressions including all factors reported in Table 1 and 2 were performed for the three types of neonatal injuries. A short second stage of labor (<20 min) remained the only factor related and protective for neonatal injury at birth, neonatal injury at discharge and Erb's palsy. A maternal BMI30 kg/m2 was associated with neonatal injury at discharge and Erb's palsy with a P<0.20 and remained included in the regression analysis, but it did not reach statistical significance (P=0.07 and 0.06).

Table 2 Stepwise logistic regression for factors associated with neonatal injury

Comment

Neonatal injury following delivery is an important area of study. Initially thought to be solely the result of excessive traction following delivery of the fetal head, many studies suggest that this may not be the case. Injury can also occur after normal delivery, cesarean section, and in the posterior shoulder of a vaginal delivery, which suggests that antepartum and intrapartum forces may be at work in some of these cases.2, 10, 11 As neonatal morbidities such as brachial plexus injuries are more commonly associated with its occurrence,5 shoulder dystocia remains a feared obstetric outcome. It is therefore of importance to understand what factors in shoulder dystocia may be associated with neonatal injury. This is what we evaluated in our own population of shoulder dystocia patients.

First, we found that neonatal injury at discharge in shoulder dystocia patients was associated with maternal weight, but more precisely with maternal BMI. In the regression analyses, the maternal BMI >30 kg/m2 was the factor related to maternal obesity that was the most associated with neonatal injury at discharge and Erb's palsy. It may not have reached statistical significance possibly because of type 2 error, given that the number of infants with neonatal injury at discharge was 25, 19 with Erb's palsy. Nonetheless, previous data regarding the role of maternal obesity in shoulder dystocia and neonatal injury are conflicting.12, 13 Cedergren et al. found an association between morbidly obese mothers and increased risk of shoulder dystocia (OR 2.14, 95% CI 1.83–2.49).13 A recent publication, however, did not show an independent association between maternal obesity and neonatal birth injury.6 In fact, other studies also suggest that maternal obesity is not associated with shoulder dystocia once other factors are accounted for by logistic regression.14, 15 Our results, in contrast, suggest that in a situation of shoulder dystocia, maternal obesity can lead to a difficult delivery, possibly by way of soft tissue dystocia and difficulty using maneuvers to resolve the problem and therefore can increase the rate of neonatal injuries. It is possible as well that maternal obesity may lead to changes in physician practice as well, in turn leading to a change in outcomes.

Secondly, we found that a second stage of labor <20 min was statistically less frequent in neonates with injuries. This provides reassurance that when a shoulder dystocia occurred in the setting of a short second stage of labor, the likelihood of neonatal injuries is lower.

Finally, we found that a neonatal birth weight >4500 g was related to neonatal injuries in cases of shoulder dystocia. This factor did not remain statistically significant after adjusting for confounding factors. While it is clear that birth weight >4500 g is an important risk factor for shoulder dystocia, and therefore a risk factor for neonatal birth injuries,7, 16 our findings suggest that the effects of birthweight may be related to length of second stage or other factors that act as either confounders or on the causal pathway. Furthermore, as birthweight is difficult to determine antenatally, it is less important predictive factor related to the presence or severity of shoulder dystocia.

While our study is one of the first to report predictors of neonatal injury in the setting of shoulder dystocia, it is not without limitations. While shoulder dystocia cases were identified using both ICD-9 coding during delivery and the hospital perinatal database as well as review of these charts, ascertainment bias is a possibility. This is of particular concern in cases where shoulder dystocia was not recognized or recorded. Neonates with birth injury that did not have documented shoulder dystocia were not evaluated. Further, we only evaluated the presence of injury to the time of discharge; long-term follow-up for permanent injury was not available. Additionally, as mentioned above, because the number of injuries was small, statistical power to examine and identify associated risk factors may have been limited by sample size. Finally, variation in physician practice in the presence of various factors may have influenced delivery management, which may lead to biases between these factors and the neonatal outcomes we examined.

Even with these limitations, this study provides useful information regarding key risk factors in shoulder dystocia outcomes and their relationship to the primary morbidity of shoulder dystocia, neonatal injury. Ultimately, as many studies have demonstrated, shoulder dystocia and its outcomes may be unavoidable without a high number of cesarean sections and the associated medical and financial cost. Information about risks, however, can guide clinicians when managing patients in labor, particularly those at increased risk for shoulder dystocia.

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Correspondence to S H Mehta.

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Mehta, S., Blackwell, S., Bujold, E. et al. What factors are associated with neonatal injury following shoulder dystocia?. J Perinatol 26, 85–88 (2006). https://doi.org/10.1038/sj.jp.7211441

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Keywords

  • shoulder dystocia
  • neonatal injury
  • brachial plexus injury
  • macrosomia

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