title: Fetal age assessment based on ultrasound head biometry and the effect of maternal and fetal factors.
abstract: BACKGROUND
  Maternal height and weight have increased during the past 20 years, as has birthweight. The aim of the present study was to establish new reference charts for gestational age (GA) assessment using fetal biparietal diameter (BPD) and head circumference (HC), and to determine the effect of maternal and fetal factors on age assessment.
  
  
  METHODS
  This was a prospective, cross-sectional study of 650 healthy women with regular menstrual periods and singleton uncomplicated pregnancies, recruited after written consent. BPD (outer-outer) and HC were measured at 10-24 weeks of gestation. We used regression analysis to construct mean curves and assess the effect of maternal and fetal factors on age assessment.
  
  
  RESULTS
  BPD and HC were successfully measured in 642 participants. Using BPD and HC before 20 weeks, the new charts gave 3-8 days higher GA assessment than the charts presently in use, and <1 day difference compared to other recently established charts. Maternal age, multiparity, fetal gender, breech position and shape of fetal head affect GA estimation by 1-2 days when using BPD (p = 0.0001-0.02). Only maternal age and fetal gender affected GA estimation when using HC (</= 1 day, p = 0.001).
  
  
  CONCLUSIONS
  Our new charts for assessing gestational age based on fetal head biometry are notably different from charts presently in use. Maternal and especially fetal factors affect gestational age assessment when using BPD, but less so for the HC method, which is suggested as the more robust method.
authors.affiliation: Department of Obstetrics and Gynecology, Haukeland University Hospital and University of Bergen, Norway. synnove.johnsen@helse-bergen.no
authors.forename: Synnøve Lian
authors.initials: SL
authors.lastname: Johnsen
authors.forename: Svein
authors.initials: S
authors.lastname: Rasmussen
authors.forename: Rita
authors.initials: R
authors.lastname: Sollien
authors.forename: Torvid
authors.initials: T
authors.lastname: Kiserud
mesh_terms: D000293:Adolescent; D000328:Adult; D001699:Biometry; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006257:Head / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000196:embryology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D011446:Prospective Studies; D012016:Reference Values; D016216:Ultrasonography, Prenatal