The influence of maternal body mass index on interobserver variability of fetal ultrasound biometry and amniotic fluid assessment in late pregnancy.

OBJECTIVES: Determine interobserver reproducibility of fetal ultrasound biometry and amniotic fluid assessment in the third trimester according to BMI categories. METHODS: 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. RESULTS: 110 women 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. CONCLUSIONS: Obesity does not seem to negatively impact the reproducibility of fetal biometric parameters when undertaken by experienced physicians/sonographers. This article is protected by copyright. All rights reserved.