A Comparison Of Two Formulae For Estimating Fetal Weight At Term By Ultrasonography With Actual Birth Weight

Abstract

Background: Ultrasonography has proved to be a simple, important and non-invasive diagnostic tool to measure fetal weight. It is a basic diagnostic tool in obstetrics and its benefits extend from use in diagnosis of very early pregnancy to estimation of fetal weight at term. Fetal weight estimation has a significant bearing in management decisions in labour, thereby markedly improving perinatal outcome.
Objective: The objective of the study was to compare ultrasound estimated fetal weight at term by the Hadlock II and IV formulae with actual birth weight.
Methods: Cross sectional comparative study carried out at the Lagos University Teaching Hospital from May to August 2015.It comprised100 obstetric patients of all parities that met the criteria for inclusion in the study. They were counselled to gain their consent. All participants were from all social economic classes and obstetric ultrasound scan was done at no cost to the participants.
The ultrasound machine in our labour ward was used. A 3.5 MHz transducer was used for ultrasound measurement. Hadlock  11--BPD,AC and FL and Hadlock 1V combines BPD,HC,AC and FL.Data were obtained using data collection form specifically designed for this study. Data was analysed using the statistical package for social science (SPSS)-20.
Results: There were 100 women who met the inclusion criteria during the period of study. Their age ranged from 18 to 43 years with mean age of 31.19 +5.73. Their parity ranged from 0 to 7. The mean gestational age was 38.8+1.42 weeks and ranged between 37 and 41 weeks. The social class of the participants were derived using the method described by Olusanya et al. Twenty six percent were
of low socioeconomic class, 59% were middle class while 15% were high class. Therefore, the population was predominantly middle and low socioeconomic class. The estimated weight using Hadlock II Formular ranged between 2.22kg and 4.23kg with a mean value of 3.23+ 0.44kg while the estimated weight using Hadlock IV ranged between 2.24kg and 4.23 with a mean value of 3.25+0.4kg.The actual birth weight ranged from 2.30 to 4.30 with a mean value of 3.28+ 0.45kg. The scan delivery interval ranged from 2 hours to 72 hours with a mean of 17.56+15.76 hours. There was a statistically significant positive correlation between weight predicted using Hadlock
II formular and actual birth weight. P value (at 95% 2 confidence interval) was <0.001, R =0.0924, t=3.833. There was also a statistically significant positive correlation between actual birth weight and weights predicted using the Hadlock IV formular, 2 P<0.022, R =0.933, t=2.326. However, Hadlock IV was more positively correlated with actual birth weight. Both formulae had 100% accuracy in estimating low birth weight babies. Hadlock II had 93% accuracy in estimating fetal macrosomia while Hadlock IV had 94% accuracy. All (i.e 100%) of the predicted weights using ultrasound scan (using both Hadlock II and IV formulae) were within +10% of the actual birth weight.
Conclusion: Hadlock IV may be better than Hadlock II because it has the least absolute mean difference with mean actual weight, higher correlation coefficient with actual weight and higher accuracy in estimating fetal macrosomia.

Keywords: ultrasonography, Hadlock II, Hadlock IV, Estimated fetal weight, Actual birth weight