1096 Association between ultrasound markers of disproportionate fetal abdominal growth and shoulder dystocia

Abstract

To evaluate the association between shoulder dystocia (SD) and fetal abdominal adiposity, measured via the Fetal Abdominal Adiposity Score (FAAS), a novel ultrasound-based metric. 23,862 third trimester ultrasounds of singleton pregnancies delivered at a tertiary care center 2007-2017 were used to develop normative data by gestational week for the FAAS, which was calculated as follows: biparietal diameter minus fetal abdominal diameter (abdominal circumference/pi). FAAS was calculated from the last ultrasound before delivery in two cohorts of singleton pregnancies delivered vaginally at the same institution: (1) patients with a delivery complicated by SD in 2007-2019 followed by another vaginal delivery in the same period, and (2) a cohort of all women who delivered vaginally after undergoing third-trimester ultrasound Jan 2018–Jun 2019. Receiver operating characteristics (ROC) curves were generated and the area under the curve (AUC) calculated for the FAAS, abdominal circumference (AC) percentile (%ile), and estimated fetal weight (EFW) %ile in each cohort. Rates of SD were assessed at predefined percentiles. Recurrent SD occurred in 5 of 32 vaginal deliveries with a prior SD (16%). AUC and 95% confidence intervals in this cohort were: FAAS 0.73 (0.52, 0.94), AC %ile 0.82 (0.65, 0.99), EFW %ile 0.70 (0.48, 0.92), with similar performance between measures (p=>0.10). Optimal cutoffs (value, sensitivity, specificity) were: FAAS 75 (80%, 59%), AC 61%ile (100%, 59%), EFW 42%ile (100%, 22%). SD occurred in 46 of 3,902 deliveries in the unselected cohort (1.2%). All metrics performed poorly in this cohort (AUC <0.60) with no significant difference in performance between measures. Risk of SD increased with increasing FAAS in both cohorts (Table 1, Table 2), with FAAS ≤50 carrying a 6% risk of recurrent SD, and FAAS >50 carrying a 25-50% risk. FAAS and AC%ile show promise for delivery risk-stratification of patients with prior SD. If validated prospectively in larger cohorts, these metrics may help to safely prevent the first Cesarean in patients at low risk of recurrent SD.View Large Image Figure ViewerDownload Hi-res image Download (PPT)