Are there differences in mechanical fetal response between routine and shoulder dystocia deliveries?

Abstract

AND SHOULDER DYSTOCIA DELIVERIES? ROBERT ALLEN, STEPHANIE CHA, LINDSAY KRANKER, TARA JOHNSON, EDITH GUREWITSCH, Johns Hopkins University, Biomedical Engineering, Baltimore, Maryland, Johns Hopkins University, Gynecology and Obstetrics, Baltimore, Maryland OBJECTIVE: Previous simulations of shoulder dystocia (SD) explored the effect of SD itself on the mechanical response of the fetus. Our objective was to perform an experimental study to explore the variations in fetal response due to routine, unilateral SD (USD) and bilateral SD (BSD) deliveries. STUDY DESIGN: Using a biofidelic maternal model, an instrumented fetal model and a data-acquisition system, we performed 30 experiments. For routine deliveries, we engaged the fetal head and allowed it to progress through cardinal movements using typical uterine contraction forces of 20-35 lbs, stopping the delivery when the head restituted to LOA presentation. For USD deliveries, we obstructed the anterior shoulder on the symphysis pubis; for BSD, the posterior shoulder was also impacted on the sacral promontory. Fetal shoulder widths were varied from 11.5, 12.9 and 12.1 cm, respectively for routine, USD and BSD deliveries. For each delivery we continuously measured head rotation (HR), brachial plexus (BP) stretch and neck extension (NE), selecting peak values for analysis. Maximum BP stretch, NE and HR were compared among groups using ANOVA, with P!0.05 considered significant. RESULTS: The table lists mean peak BP stretch, HR and NE among routine, USD and BSD deliveries. There are no differences among the three types of delivery for anterior BP stretch, HR and NE. CONCLUSION: Quantifiable mechanical response occurs in routine and SD deliveries. Posterior BP stretch is significantly longer for routine deliveries than either USD or BSD deliveries.