The relation between fetal abdominal circumference and birthweight: findings in 3512 pregnancies

Authors

  • G. C. S. Smith,

    Registrar , Corresponding author
    1. Department of Obstetrics and Gynaecology, University of Glasgow, The Queen Mother s Hospital, Yorkhill NHS Trust, Glasgow
      Correspondence: Dr G. C. S. Smith, Laboratory for Pregnancy and Newborn Research, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401, USA.
    Search for more papers by this author
  • M. F. S. Smith,

    Lecturer
    1. Department of Computer Science, Bell College of Technology, Almada Street, Hamilton
    Search for more papers by this author
  • M. B. McNay,

    Consultant (Obstetric Ultrasound)
    1. Department of Obstetrics and Gynaecology, University of Glasgow, The Queen Mother s Hospital, Yorkhill NHS Trust, Glasgow
    Search for more papers by this author
  • J. E. E. Fleming

    Research Technologist
    1. Department of Ultrasonic Technology, University of Glasgow, The Queen Mother s Hospital, Yorkhill NHS Trust, Glasgow
    Search for more papers by this author

Correspondence: Dr G. C. S. Smith, Laboratory for Pregnancy and Newborn Research, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401, USA.

Abstract

Objectives To establish the relation between fetal abdominal circumference and birthweight in a large population of fetuses; to identify whether the error in estimating birthweight by abdominal circumference varied with the magnitude of abdominal circumference; and to establish whether adding femur length to abdominal circumference caused a clinically important reduction of error in predicting birthweight.

Design A retrospective study.

Setting The ultrasound department of a teaching maternity hospital offering a tertiary referral service.

Sample From 3512 nondiabetic women with a normally formed singleton fetus, an abdominal circumference measurement of the infant was made within seven days of delivery; of these, 1213 had a femur length measurement performed at the same time.

Results There was a linear relation between abdominal circumference and birthweight. There was a strong inverse correlation between the proportional error in predicting birthweight from the abdominal circumference and the magnitude of the abdominal circumference. Both the Campbell and Wilkin equation (abdominal circumference alone) and the Hadlock equation (abdominal circumference and femur length) were associated with systematic errors, especially with larger birthweight infants. The median absolute errors for the two equations were not significantly different overall (6.98% and 6.86% respectively), although the Hadlock equation was significantly more accurate in predicting birthweight in infants weighing greater than 4500 g. However, no threshold value of abdominal circumference or of estimated fetal weight using the Hadlock equation had a positive predictive value in estimating infants of > 4500 g of greater than 35%.

Conclusions Prediction of birthweight should be by abdominal circumference alone. Table 1 presents robust estimates of the error of predicting birthweight using fetal abdominal circumference.

Table 1.  The relation between fetal abdominal circumference (AC) and birthweight (BW).
AC (mm)nMedian BW(g)10th-90th centile BW (g)Range BW(g)
200-20913900750-1030740-1040
210-219201040830-1370780-1400
220–229201060750-1410650-1460
230-239281255980-1470900-1860
240-2493614351200-17901080-1950
250-2593715801290-19251180-2260
260-2695618351490-21901340-2400
270-2798920001640-23201390-2620
280-28913422651920-26601530-2910
290-29921925302130-29001820-3100
300-30935026852340-30802010-3420
310-31938728502470-32902110-3650
320-32948430602700-34702350-3770
330-33943932602880-37002570-3980
340-34942333803040-38602670-4240
350-35931436153240-40402890-4460
360-36924537503330-11903020-4610
370-37911738403480-43603180-4790
380-3896641403660-46403470-4820
390-3993542903665-46753640-5000

Ancillary