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Optimal timing of ultrasonographic assessment of uterine contractility in primary cesarean deliveries
Abstract Number: F3B-526
Abstract Type: Original Research
Introduction: Uterine atony remains the leading cause of maternal hemorrhage following cesarean delivery. Assessment of uterine contractility is critical for appropriate identification and treatment of atony. Current methods of measuring uterine tone are subjective and operator-dependent. Intraoperative ultrasound (US) has been proposed as an alternative means of objectively assessing uterine tone.
Our previously presented case series demonstrated a correlation between posterior uterine wall thickness as measured by US and the subjective assessment of uterine tone by the obstetrician (OB). We conducted an IRB-approved prospective evaluation of uterine tone, as measured by US, in patients expected to have normal uterine contraction following cesarean delivery. Our goal was to identify the appropriate time points during the procedure at which US will reliably evaluate uterine tone.
Methods: We recruited and evaluated 35 patients who presented for primary cesarean delivery. The primary outcome was US-measured thickness of the posterior uterine wall at 3 time points during surgery: immediately after externalization (T1), 5 minutes later (T2), then immediately prior to internalizing the uterus (T3). The secondary outcome was the subjective uterine tone score given by OB providers at each corresponding time point.
Results: 23 patients were included in our final analysis. The difference in measured posterior uterine wall thickness from T1-T2 and T2-T3, and in corresponding OB subjective uterine tone scores, were both found to be statistically significant (Table 1). A mean increase of 3.25 mm in the T1-T2 interval represented an early worsening of uterine tone, and a mean decrease of 2.95 mm in the T2-T3 interval represented improving tone after activation of oxytocin receptors. We further stratified the data for T2-T3 based on elapsed time to identify the ideal time interval between measurements.(Graph 1-2, Table 2)
Discussion: We observed that uterine wall thickness increased from T1-T2, however shortened from T2-T3. This statistically significant change likely corresponds to delayed uterine contraction after delivery. Thus, the most accurate US assessment of uterine tone may come from evaluating the difference in posterior uterine wall thickness between hysterotomy closure (T2) and at least 5 mins later. We believe US-guided measurements of posterior uterine wall thickness can reliably evaluate uterine tone, thereby eliminating inter-individual variability.