High birth weight, induction boosted shoulder dystocia risk.
High birth weight, however, remained a leading risk factor for shoulder dystocia, Joseph Ouzounian, M.D., reported at the annual meeting of the Pacific Coast Obstetrical and Gynecological Society.
The study included 267,228 vaginal births that took place between 1991 and 2001 at a 10-hospital Kaiser Permanente system in Southern California. During that period 1,686 cases (0.6%) of shoulder dystocia were reported, said Dr. Ouzounian, chief of obstetrics and gynecology and director of maternal/fetal medicine at Kaiser Permanente, Baldwin Park, Calif.
Rates of maternal diabetes and vacuum or forceps use were not significantly different between the shoulder dystocia and no shoulder dystocia groups. Rates of oxytocin use (14.4% vs. 10.4%, respectively) and labor induction (24.5% vs. 16.9%, respectively) were higher in the shoulder dystocia group, however. These differences between groups were statistically significant.
The standout statistic, however, was birth weight, with 19.3% of shoulder dystocia cases associated with a birth weight of more than 4,500 g, compared with 1.5% of non-shoulder dystocia cases.
A total of 56% of shoulder dystocia cases were associated with a birth weight of more than 4,000 g, compared with 9.6% of non-shoulder dystocia cases.
"We saw a striking difference in birth weight, with about a 15-fold difference between the shoulder dystocia group and non-shoulder dystocia group," Dr. Ouzounian said.
Limitations in estimating accurate birth weight antenatally, however, prevent its use as a practical means of predicting shoulder dystocia, he added.
While the clinical triad of oxytocin use, labor induction, and birth weight of more than 4,500 g yielded an odds ratios of 23.2 for shoulder dystocia, its sensitivity and positive predictive value were only 12.4% and 3.4%, respectively. (Dr. Ouzounian did not report specificity or negative predictive value data for the triad.)
"The clinical relevance of this for doctors on the front line is delineated by the fact that fetal weight estimates can still be unreliable," he said at the meeting, cosponsored by the American College of Obstetricians and Gynecologists.
Contrary to previous findings, the current research did not show that operative vaginal delivery or maternal diabetes had a significant impact on shoulder dystocia rates. Dr. Ouzounian said this may have been due to the larger size of his study, in addition to decreasing rates of vacuum and forceps use.
In a commentary on the study, Roydon Steinke, M.D., of Fresno, Calif., emphasized the need to find better predictors for shoulder dystocia. "Professionals would like to predict shoulder dystocia in order to avoid it and its consequences," he said at the meeting. "Besides rendering the baby disabled for life in some cases, it's devastating for the parents and for the health care team."
Litigation stemming from shoulder dystocia has resulted in jury awards ranging from tens of thousands to tens of millions of dollars, he said. But with the odds ratio of the potential predictors of induction, oxytocin, and birth weight appearing so low in Dr. Ouzounian's study, options are limited, said Dr. Steinke.
"Simplistically, you'd have to do a lot of cesarean sections and expose patients to a lot of potential morbidity just to prevent a few shoulder dystocias," he said.
BY NANCY A. MELVILLE