A comparison of clinical and ultrasound estimation of fetal weight

The accuracy of clinical and ultrasound estimation of fetal weight was compared by an analytical cross sectional study. 266 pregnant women who were admitted to the labour room, Siriraj Hospital during the period from February 1, 1999 to March 1, 1999 were included in this study. Fetal weight was estimated in all pregnant women clinically by 2nd year resident physicians and 6th year medical students, followed by ultrasound estimation within 24 hours before delivery. Every estimation was blinded from each other. From the study, clinical estimation by 2nd year resident physicians was comparable with ultrasound estimation and both were significantly more accurate than estimation by 6th year medical students. The proportions of accuracy were 66.7 per cent, 63.3 per cent and 55.3 per cent respectively. Clinical estimation by 2nd year resident physicians tended to have equally over- and underestimation. On the contrary, ultrasound estimation tended to underestimate when the method was inaccurate. Among infants with a birth weight less than 2,500 grams, ultrasound estimation performed slightly better than clinical estimation. However, every method underestimated the fetal weight when an infant weighed more than 4,000 grams. In conclusion, accuracy of clinical estimation of fetal weight by 2nd year resident physicians was comparable to that of ultrasound estimation and may be used as an alternative to ultrasound estimation for pregnant women. However, when the clinical estimate of fetal weight is less than 2,500 grams, ultrasound estimation should be performed for more accurate results and also for assessment of other abnormalities. Careful attention should be paid to infants with a birth weight of more than 4,000 grams since no method can correctly estimate the fetal weight and physicians should be aware of birth trauma.