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 ¼ 0.0001-0.02). Only maternal age and fetal gender affected GA estimation when using HC ( 1 day, p ¼ 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.

Intrauterine growth restriction

“…Up to 30 weeks (60 mm), dating based on BPD measurement virtually coincided with dating obtained by Hadlock et al using a multiparameter method [4]. New Norwegian reference norms for BPD and HC are also similar to those in the British charts [5]. A study of 152 singleton pregnancies conceived in vitro showed that HC was most accurate when only a single parameter was used to determine gestational age [6].…”

Prediction of adverse perinatal outcome of small-for-gestational-age pregnancy using size centiles and conditional growth centiles

“…Voluson 730 Expert E6 and E8 (GE Medical Systems, Kretz Ultrasound, Zipf, Austria) ultrasound scanners were used for the measurements. The measurements included fetal head circumference 15,17 , abdominal circumference 17 and femur length 17,18 . EFW was calculated according to Combs formula 19 .…”

A new population‐based term prediction model vs. two traditional sample‐based models: validation on 9046 ultrasound examinations

“…A newly developed obstetric wheel 'Terminhjulet' ('Bergen-2004') 25,26 is based on the same principles 20 as Trondheim-1984, but uses a newer data sample and fractional polynomial regression analysis. This model was constructed from a prospective, cross-sectional study of 650 healthy women with regular menstrual periods and singleton, uncomplicated pregnancies.…”

“…The BPD prediction tables for Trondheim-1984 are available from this prediction model 24 . For Bergen-2004, the BPD-and FL-tables in the articles show the computed gestational age, but the accompanying published formulae 25,26 are in error. The intended formulae 22 have been provided by S. L. Johnsen (pers.…”