66 Influence of maternal body mass index on interobserver variability of fetal biometry in late pregnancy

Abstract

Reproducibility of ultrasound based fetal biometry in the third trimester is important, as this is the period when growth assessment is most likely to influence clinical decisions. Clinical experience suggests that increased BMI is associated with suboptimal biometric measurements, but surprisingly the evidence on the effects of maternal obesity on interobserver variation is scant. We sought to determine interobserver reproducibility of fetal ultrasound biometry and amniotic fluid assessment in the third trimester according to BMI categories Prospective cohort of women with singleton gestations beyond 34 weeks, recruited into 4 groups according to BMI categories: normal, overweight, obese and morbid obese. Multiple pregnancies, diabetes, growth and fetal abnormalities were excluded. Biometric and fluid measurements were obtained by two experienced physicians/sonographers, blinded for gestational age and each other’s measurements. Differences between observers were expressed as gestational age-specific Z-scores. Interobserver correlation coefficient (ICC) and Cronbach's reliability coefficient (CRC) were calculated. Bland-Altman plots were constructed to assess the level of reproducibility. 110 patients were prospectively enrolled (1,320 measurements obtained by 17 sonographers / physicians): 20 had normal BMI (18.2%), 30 were overweight (27.3%), 30 were obese (27.3%) and 30 were morbidly obese (27.3%). Except for MVP (CRC 0.66), all biometric parameters and AFI had high level of reproducibility (CRC 0.84 – 0.93). Among BMI groups: BPD had the highest level of reproducibility (CRC > 0.90); AC and FL reproducibility increased with increasing BMI while MVP decreased. Interobserver differences for biometry fell within the 95% limits of agreement. Obesity does not seem to negatively impact the reproducibility of fetal biometric parameters when undertaken by experienced physicians/sonographers. Caution should be exercised in assessing amniotic fluid in the third trimester since MVP had poor reproducibility across all BMI categories.View Large Image Figure ViewerDownload Hi-res image Download (PPT)