title: Comparison of matching by body volume or gestational age for calculation of observed to expected total lung volume in fetuses with isolated congenital diaphragmatic hernia.
abstract: OBJECTIVE
  To determine the bias induced by matching fetuses according to gestational age (GA) or fetal body volume (FBV) when calculating the observed to expected total fetal lung volume (o/e TFLV) in cases of isolated congenital diaphragmatic hernia (CDH).
  
  
  METHODS
  This was a single-center, retrospective study on archived magnetic resonance (MR) images of fetuses with isolated CDH over a 10-year period. We retrieved the TFLV, GA and o/e TFLVGA , and delineated FBV to obtain TFLVFBV in each case. We evaluated the relationship between o/e TFLVFBV and o/e TFLVGA by Bland-Altman analysis. All outliers were manually identified, and their specific clinical features were retrieved.
  
  
  RESULTS
  Records of a total of 377 MR examinations of 225 fetuses were identified and included in the analysis. The mean ( ± SD) time spent on FBV measurement was 16.12 ± 4.95 min. On reproducibility analysis of FBV measurement (n = 10), the intraobserver intraclass correlation coefficient (ICC) was 0.998 and the interobserver ICC was 0.999. FBV was highly correlated with GA (R(2)  = 0.899; P < 0.0001). There was good agreement between o/e TFLVGA and o/e TFLVFBV , with a mean difference of -1.10% and 95% limits of agreement of -8.58 to 6.39. There were no outliers in fetuses that had an o/e TFLV < 25%. Discrepancies induced by different methods were more likely in women with a body mass index ≥ 25 kg/m(2) (+16.5%), fetuses with an estimated fetal weight (EFW) ≤ 10(th) centile (+21.3%) or an EFW > 90(th) centile (+14.7%).
  
  
  CONCLUSIONS
  Discrepancies in matching by FBV and GA when calculating o/e TFLV are more likely in fetuses with an abnormal EFW or in fetuses carried by overweight women. The clinical relevance of using FBV rather than GA for calculation of the o/e TFLV might be limited, as there was no discrepancy between the two methods in fetuses with small lungs ( < 25%), which is the group of most interest for lung volume assessment.
authors.affiliation: Fetal Medicine Unit, Division of Woman and Child, Department of Obstetrics and Gynaecology, University Hospitals Leuven, Katholieke Universiteit Leuven, Leuven, Belgium; Division of Maternal Fetal Medicine, Department of Obstetrics and Gynaecology, Siriraj Hospital, Faculty of Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: K
authors.initials: K
authors.lastname: Nawapun
authors.forename: I
authors.initials: I
authors.lastname: Sandaite
authors.forename: P
authors.initials: P
authors.lastname: Dekoninck
authors.forename: F
authors.initials: F
authors.lastname: Claus
authors.forename: J
authors.initials: J
authors.lastname: Richter
authors.forename: L
authors.initials: L
authors.lastname: De Catte
authors.forename: J
authors.initials: J
authors.lastname: Deprest
mesh_terms: D049628:Body Size; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D065630:Hernias, Diaphragmatic, Congenital / Q000175:diagnosis*; D006801:Humans; D008168:Lung / Q000002:abnormalities / Q000196:embryology*; D008176:Lung Volume Measurements; D008279:Magnetic Resonance Imaging; D015588:Observer Variation; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies
keywords: congenital diaphragmatic hernia; fetal body volume; fetal lung volume; gestational age; magnetic resonance imaging