Shoulder Dystocia
Shoulder Dystocia
Abstract & Commentary
By John C. Hobbins, MD, Professor, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.
Dr. Hobbins reports no financial relationship to this field of study.
Synopsis: A recent study shows that in shoulder dystocia, if delivery occurs within 5 minutes, the rate of acidosis and hypoxic asphyxic encephalopathy is < 1%.
Source: Leung TY, et al. Head-to-body delivery interval and risk of fetal acidosis and hypoxic ischaemic encephalopathy in shoulder dystocia: A retrospective review. BJOG 2010 Dec 24; Epub ahead of print; doi:10.1111/j.1471-0528.2010.02834.x.
Despite the important progress that has been made in obstetrics, in general, over the last 20 years, shoulder dystocia remains an enigma. Given the rising rate of maternal obesity and gestational diabetes, it is unlikely that the rate of this dangerous complication will be lowered in the near future. It has been difficult enough to nail down cause and effect when dealing with the occasional morbidity associated with shoulder dystocia, but one aspect that has received some investigative attention in the past is the time that it takes after delivery of the head to get the rest of the baby out the head to body delivery interval (HBDI).
A paper recently appeared in the British Journal of Obstetrics and Gynecology in which the authors reviewed birth records from a Hong Kong University Hospital between 1995 and 2009. Of the 62,300 deliveries occurring during this time period, they found 210 cases (0.34%) that fit their liberal criteria for shoulder dystocia (the need for maneuvers other than downward traction of the head or a HBDI of > 1 minute). In 200 of these cases data were available on cord gases, Apgar scores, fetal heart rate patterns, and the presence of hypoxic, ischemic encephalopathy (HIE).
They found that "pathological" fetal heart rate patterns were associated independently with cord arterial pH, but not with base excess (BE). The length of HBDI, however, did correlate with the BE, and there was an inverse relationship with arterial pH, resulting in a drop in pH of 0.011 for every minute of HBDI. This represents a slope that is less steep than had been previously reported.1 Most importantly, the incidence of severe acidosis (pH < 7.0) and HIE were only 0.5% and 0.5%, respectively, if HBDI was < 5 minutes, and 5.9% and 23.5% if HBDI was ≥ 5 minutes.
The ancillary data also were interesting. The Asian population studied had an incidence of macrosomia (> 4000 g) of 31% when shoulder dystocia was encountered, vs the reported 44%-64% in the same subset of women in Western populations.2 However, as the authors point out, since the baseline incidence of macrosomia in Asian populations is about 4%, compared with 6%-15% in Western populations, the chance of shoulder dystocia in both populations remains basically the same. In essence, this provides further credence to the seemingly obvious concept that shoulder dystocia results from a mismatch between the size of the baby and the size of the pelvis of the mother.
Commentary
The authors' take away message is that cord pH drops with the length of HBDI, "but the rate of acidosis and encephalopathy is very low if the elapsed time is less than 5 minutes." Avoiding morbidity in shoulder dystocia does represent a race against time, and every minute seems like an hour. However, after recording the start time, and asking (shouting?) for help from the most experienced individuals available, one still has more time than was previously believed. Now the clinician can effectively navigate the shoulder dystocia "fire drill" in a controlled fashion. Hopefully, this approach will trump an instinctive reaction to move immediately to an adrenaline-infused hasty, and sometimes forceful, solution to this scary situation.
References
- Wood C, et al. The influence of differences of birth times upon fetal condition in normal deliveries. J Obstet Gynaecol Br Commonw 1973;80:289-294.
- Dildy GA, Clark SL. Shoulder dystocia: Risk identification. Clin Obstet Gynecol 2000;43:265-282.
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