Examining the Evidence
Q Does vacuum extraction increase the risk of brachial plexus palsy?
<huc>A</huc> No, unless the vacuum extraction involves shoulder dystocia, high fetal birth weight, or application of fundal pressure. Shoulder dystocia is by far the most significant risk factor for brachial plexus palsy in this context.
This excellent study provides indirect scientific evidence that shoulder dystocia is the prominent risk factor for brachial plexus palsy in the setting of vacuum extraction, with an odds ratio (OR) of 16.0 (95% confidence interval [CI] 8.9–28.7). Other independent factors include fetal birth weight of 3,999 g or more (OR 7.1; 95% CI 4.8–10.5) and application of fundal pressure (OR 1.6; 95% CI 1.1–2.3). However, 81% of the infants with brachial plexus palsy did not experience shoulder dystocia during vacuum extraction. This finding is in accord with recent studies of obstetric brachial plexus palsy.1
Duration of vacuum extraction plays a role. The authors determined that 5 minutes of vacuum extraction carries an estimated risk of brachial plexus palsy of 0.8%, whereas 25 minutes carries a risk close to 4%.
Ever since the 1978 landmark study by Benedetti and Gabbe,2 the association between operative vaginal delivery and shoulder dystocia has aroused interest. Even today, clinical questions persist when an infant experiences brachial plexus palsy in the setting of operative vaginal delivery. Did the application of the vacuum or forceps cause the neonatal injury? Was the shoulder dystocia a direct consequence of the vacuum or forceps? Given the marked decrease in forceps usage and increasing reliance on vacuum extraction, this research article is timely and clinically relevant.
Strength in numbers: 13,716 vacuum deliveries
In Sweden since 1973, all deliveries have been recorded in the Medical Birth Registry of the National Board of Health and Welfare. Using this registry, Mollberg and colleagues were able to study 13,716 deliveries involving vacuum extraction, 153 of which resulted in brachial plexus palsy. The strength of this study lies in its immense power, which yielded insight into the approximate incidence (1.1%) of brachial plexus palsy in the setting of vacuum extraction.
Some medical records were incomplete
This study had a relatively high exclusion rate of 32%, since charts were analyzed only if they possessed a completed instrumental delivery protocol. As a result, Mollberg and colleagues were able to evaluate only a limited number of factors that could potentially be tied to brachial plexus palsy: shoulder dystocia, fetal birth weight, fundal pressure, number of tractions, duration of vacuum application, parity, vacuum silicone cup, epidural anesthesia, and fetal station.
No details on fundal pressure. A surprising percentage (58%) of infants with brachial plexus palsy had fundal pressure applied. Unfortunately, no indication was given as to whether this fundal pressure was used to assist with maternal expulsive efforts, to aid with placement of the vacuum extractor, or as a maneuver to alleviate shoulder dystocia.
Prolonged second stage defined differently from ACOG standard. This study defined a prolonged second stage as longer than 60 minutes in parous women and longer than 120 minutes in nulliparous women, whereas the American College of Obstetricians and Gynecologists defines it in multiparous women as longer than 2 hours with or 1 hour without regional anesthesia, and in nulliparous women as longer than 3 hours with or 2 hours without regional anesthesia.
Another weakness: Some vacuum extractions may have been midpelvic, given that cases with the fetal vertex at the level of the ischial spine were allowed.
Take-home message: Don’t retire the vacuum extractor
There is no reason obstetricians should stop using the vacuum extractor for fear of brachial plexus palsy. However, they should continue to:
- minimize the duration of application,
- monitor the rate of fetal descent and,
- as always, employ sound clinical judgment.3
The author reports no financial relationships relevant to this article.
1. Gherman RB, Chauhan S, Oh C, Goodwin TM. Brachial plexus palsy. Fetal Maternal Med Rev. 2005;16:1-23.
2. Benedetti TJ, Gabbe SG. Shoulder dystocia: a complication of fetal macrosomia and prolonged second stage of labor with midpelvic delivery. Obstet Gynecol. 1978;52:526-529.
3. American College of Obstetricians and Gynecologists. Operative Vaginal Delivery. ACOG Practice Bulletin Number 17. Washington, DC: ACOG; 2000.