title: Fetal biparietal diameter: a critical re-evaluation of the relation to menstrual age by means of real-time ultrasound.
abstract: The relationship between fetal biparietal diameter (BPD) and menstrual age was determined by cross-sectional analysis of 533 fetuses (12 to 40 weeks) examined with a linear array real-time (dynamic image) scanner using specifically defined methodology. Mathematical modeling of the data demonstrated that the optimal fit was the linear cubic function (r2 = 99 per cent); predicted BPD values calculated from the function were most comparable with composite data from cross-sectional studies performed with static scanners after 1974 (average difference, 0.22 mm) and least comparable with composite data from cross-sectional studies performed with static scanners before 1974 (average difference, 2.0 mm). The variability associated with predicting menstrual age from the BPD increased progressively throughout gestation; the maximal variability was noted between 36 and 42 weeks (+/- 3.6 weeks). Comparison with our longitudinal study of BPD growth indicates that the cross-sectional data represent a valid estimate of the true longitudinal BPD growth curve of the population.
mesh_terms: D002508:Cephalometry / Q000379:methods; D005314:Embryonic and Fetal Development; D005260:Female; D005544:Forecasting; D005865:Gestational Age; D006801:Humans; D016014:Linear Models; D011247:Pregnancy; D012886:Skull / Q000000981:diagnostic imaging* / Q000196:embryology*; D016216:Ultrasonography, Prenatal