Reliability of period of gestation determined by
ultrasound scan measurements
International Journal of Collaborative Research on
Internal Medicine & Public Health, 2011 - Vol.
Author: Chrishantha Abeysena (1) *, Pushpa
(1) Senior Lecturer
/ Department of Public Health, Faculty of Medicine,
University of Kelaniya, Ragama, Sri Lanka
(2) Professor / Department of Public Health, Faculty of
Medicine, University of Kelaniya, Ragama, Sri Lanka
* Corresponding author
To determine reliability of period of gestation
determined by three independent raters using four
different foetal measurements.
One hundred and eighty pregnant women
were divided into three equal groups. Each group was
assigned a rater to perform ultrasound scan to measure
bi-parietal diameter, femur length, abdominal
circumference and head circumference and to compute the
respective periods of gestation using these four
measurements. Reliability between periods of gestation
derived by each rater from above four measurements were
analysed using repeated measure ANOVA. Results were
expressed as intra-class correlation coefficients (ICCs)
and coefficients of variation (CsOV).
For Raters I (F= 6.47; p=0.001) and II,
(F= 4.80; p= 0.003), computations using abdominal
circumferences resulted in the lowest mean periods of
gestation (PsOG). For Rater III, computations using both
femur length and abdominal circumference resulted in the
lowest mean periods of gestation (F= 7.5; p=0.001). ICCs
were 0.73 (95%CI 0.64–0.81) for Rater I, 0.78 (95% CI
0.70–0.85) for Rater II and 0.87 (95% CI 0.81– 0.91) for
When comparing CsOV, the highest
variation for Raters I and III was observed for femur
length. For Rater II it was bi-parietal diameter. The
lowest variation for Rater I was observed for head
circumference and for Raters II and III for abdominal
circumference. The highest CsOV of all the PsOG were
demonstrated by Rater III.
comparing the differences between the highest and the
lowest values for each period of gestation determined,
the difference was more than two weeks for 38% (n=23),
24% (n=14) and 22% (n=13) of observations made by Raters
I, II and III respectively.
Reliability of period of gestation depends on the type
of measurement taken, method of assessment and the rater
who performs the measurements. Our findings are not
conclusive enough to recommend any PsOG based on
specific measurement more reliable than others.
In-service training of the obstetricians is likely to
improve the reliability of PsOG determined using ultra
sound scan measurements.
Gestational age, pregnancy duration, reliability,
How to cite this article:
Abeysena C, Jayawardana P. Reliability of period of gestation determined by
ultrasound scan measurements. International Journal of Collaborative Research
on Internal Medicine & Public Health. 2011; 3(5):334-339.