Shoulder dystocia: What is the legal standard of care?
It’s your job to educate the jury that, even in the best of hands, permanent brachial plexus injuries can occur
IN THIS ARTICLE
Why dystocia cannot be predicted
…despite known risk factors
The risk of shoulder dystocia is higher in women with diabetes,2-5 a macrosomic fetus,2,6-8 obesity,5,8 or a previous shoulder dystocia.9-11 The problem: The predictive value of these factors is so low and their false-positive rate so high they cannot be used reliably in clinical decision-making.11-13
Prevention is impossible
Even if prediction were possible, the only preventive option is elective cesarean section. After all, this is the only intervention that might potentially avoid the infrequent but dreaded outcomes of asphyxia and permanent brachial plexus injury. But as the literature shows, even this is not an absolute guarantee.14,15 Moreover, the strategy of inducing labor several weeks prior to the due date to prevent a baby from becoming “too big” has been shown in many studies to be ineffective in lowering the shoulder dystocia rate.16-18
Risk factors are not clinically useful
The American College of Obstetricians and Gynecologists (ACOG) and Williams Obstetrics concur that risk factors for shoulder dystocia cannot be applied in a clinically useful way to prevent brachial plexus injury. As the ACOG practice bulletin on shoulder dystocia19 observes:
- “Shoulder dystocia cannot be predicted or prevented because accurate methods for identifying which fetuses will experience this complication do not exist.”
- “Elective induction of labor or elective cesarean delivery for all women suspected of carrying a fetus with macrosomia is not appropriate.”
Identify highest risk
Nevertheless, there are generally accepted guidelines for attempting to ascertain which patients are at the absolute highest risk for shoulder dystocia:
- Any woman with gestational diabetes. For any given week of gestation in the third trimester, the ratio of thorax and shoulder size to head volume is larger in babies of diabetic mothers.20 Thus, in these women, it is important to estimate fetal weight near term to determine whether a trial of vaginal delivery makes sense.
- If, for any reason, the fetus appears to be larger than average. Indications of size may come from palpation of the maternal abdomen, fundal height measurements significantly greater than dates, ultrasound estimation of large fetal weight, or maternal perception. In these cases, ultrasound imaging is advisable near term to estimate fetal weight. This estimate can be factored into the selection of delivery mode.
How big is “too big”?
There are 2 problems with using estimates of fetal weight in determining mothers and babies at highest risk:
- How is “too big” defined?
- What action should one take if a baby is thought to be “too big”?
As for what to do if a fetus is estimated to be in this size range, ACOG states: “Planned cesarean delivery to prevent shoulder dystocia may be considered [emphasis added] for suspected fetal macrosomia within the above weight parameters.”19 The decision as to whether to recommend or perform a cesarean section in these circumstances is intentionally left up to the physician and the patient.
The problem, of course, is that all our data are from measurements of babies after delivery—information obstetricians do not have at the time they must decide on the mode of delivery.
TABLE
How fetal weight affects the rate of dystocia
| ESTIMATED FETAL WEIGHT | RATE OF SHOULDER DYSTOCIA (%) | |
|---|---|---|
| NONDIABETIC MOTHERS | DIABETIC MOTHERS | |
| 1.1 | 3.7 | |
| 4,000–4,499 g | 10 | 23.1 |
| >5,000 g | 22.6 | 50 |
| Source: Acker D et al2 | ||
Choosing a mode of delivery: Not so simple
The obstetrician must determine whether the risk of shoulder dystocia is high enough to outweigh the risks to a mother of elective cesarean section. This is far from simple. Although it is true that women at the highest risk for dystocia—those with gestational diabetes and suspected macrosomia— have a risk for shoulder dystocia somewhere between 25% and 50%, this is not the main concern.
The main concern is this: What percentage of even these high-risk patients will have a shoulder dystocia that results in a permanent brachial plexus injury? The answer: Permanent injury is rare, even in highest-risk cases.
Only 10% to 20% of infants born after shoulder dystocia suffer brachial plexus injuries.16,21-23 Of these, only 10% to 15% are permanently injured.5,24,25 Thus, even in women at highest risk, the odds of having an infant with permanent brachial plexus injury are roughly 1 in 450.14 In women at lower risk for shoulder dystocia, the odds of permanent brachial plexus injury are much lower: somewhere between 1 in 2,500 and 1 in 10,000.
