title: Common fetal measurements: a comparison between ultrasound and magnetic resonance imaging.
abstract: BACKGROUND
  Ultrasound has been the method of choice for antenatal fetal assessment for the past three decades; however, problems may arise in cases of oligohydramnion, unfavorable position of the fetus, and maternal obesity.
  
  
  OBJECTIVE
  To compare ultrasound (US) and magnetic resonance imaging (MRI) for common fetal measurements at 19-30 weeks' gestation, and to assess the effect of high maternal body-mass index (BMI).
  
  
  METHODS
  59 low-risk singleton pregnancies were enrolled in a prospective blinded cross-sectional study. In a first session, an experienced obstetrician used a high-resolution US technique and in a second session on the same day MRI was used to measure biparietal diameter (BPD), head circumference (HC), mean abdominal diameter (MAD), abdominal circumference (AC), and femur length (FL). Inter- and intraobserver and intermodality variability was determined using Bland-Altman plots. The effect of maternal BMI was assessed using Spearman's statistics.
  
  
  RESULTS
  A total of 45 women aged 19-43 years (median 29 years) attended both US and MRI at median 22 weeks' gestation. The mean differences between US and MRI were 1.6 mm for HC (95% confidence interval [CI] -1.0, 4.3 mm), 1 mm for AC (95% CI -0.2, 4.0 mm), 0.2 mm for MAD (95% CI -0.7, 1.2 mm), 2.2 mm for BPD (95% CI 1.7, 2.7 mm), and 4.6 mm for FL (95% CI 2.9, 6.4 mm). Maternal BMI did not affect the results (Spearman' rho 0.054-0.277; P=NS). The intraobserver agreement for all MRI measurements was acceptable, except for FL, while the interobserver agreement was poor.
  
  
  CONCLUSIONS
  There was good agreement between US and MRI for common fetal measurements, but not for all (i.e., BPD and particularly FL). MRI had a poor interobserver agreement, underscoring the need for technical refinement and reference ranges specifically established for MRI.
authors.affiliation: Department of Radiology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Anagha P
authors.initials: AP
authors.lastname: Parkar
authors.forename: Øystein E
authors.initials: ØE
authors.lastname: Olsen
authors.forename: Knut
authors.initials: K
authors.lastname: Gjelland
authors.forename: Torvid
authors.initials: T
authors.lastname: Kiserud
authors.forename: Karen
authors.initials: K
authors.lastname: Rosendahl
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D047109:Fetal Development; D005865:Gestational Age; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011247:Pregnancy; D011446:Prospective Studies; D015203:Reproducibility of Results; D016216:Ultrasonography, Prenatal / Q000379:methods*