Clinical Versus Ultrasound Estimation of Fetal Weight

EDITORIAL COMMENT: In clinical medicine there is always the tendency to grant authenticity to an opinion expressed in a typewritten report concerning a pathology or radiology investigation and to override the clinician's opinion which in truth is often more accurate. Obstetricians are well aware of the fallibility of their clinical judgement and this applies to the outcome of trial of labour, and assessment of fetal weight; thus clinical opinion tends to be unjustifiably underrated. In this series from West Malaysia the clinicians were more than equal to the technology of ultrasonography. However, this is not the end of the story since the importance of estimation of fetal size is when the baby is small and of questionable viability (is it over 800 g and worth a Caesarean section for a fetal indication, or less than 600 g and not?), or large enough to warrant Caesarean section because of the risk of severe morbidity from shoulder dystocia or uterine rupture if the patient has had a previous Caesarean or has a breech presentation. Although there are occasions when fetal weight in excess of 4,000 g would indicate Caesarean section (breech presentation), usually a trial of labour is indicated when the infant is large and presents cephalically because the vast majority are delivered uneventfully. It is more important for the clinician to judge when to do a Caesarean section for arrest of the big head in the midpelvis rather than to perform elective abdominal delivery. In the editor's experience ultrasonography is often very useful and accurate in assessment of fetal weight at gestations below 30 weeks; fetal weight is most likely to be underestimated by the clinician when the fetus is premature and growth retarded - the head is often deeply engaged and associated oligohydramnios causes the clinician to undercall fetal size. How many Caesarean sections would have been performed in retrospect, in patients with premature rupture of the membranes breech presentation, had it been known that the birth-weight exceeded 800 g? In the case of cephalopelvic disproportion there is too much emphasis on fetal weight rather than the size and shape of the baby's skull - it is the head and/or shoulders that obstruct labour, not total body weight! Summary: A prospective study was carried out on 50 patients who had their fetal weight estimated by 3 clinicians of different seniority and compared to the ultrasound estimated fetal weights using 3 different formulas. All the patients delivered within 24 hours of their clinical and ultrasound estimates. A wide range of birth-weights (1,800-4,500 g) was estimated among the 3 different races (Malay, Chinese and Indians). The results showed that there was no significant difference in birth-weight estimation amongst the 3 clinicians as well as between the 3 ultrasound formulas used. There was however significant difference between these 2 groups when compared with the actual birth-weight with clinical estimation being superior to ultrasound estimation in our population. This level of significance did not extend beyond 4,000 g fetal weight (actual) thus making both clinical and ultrasound estimation of fetal weight equally accurate after 4,000 g. This has important implications for developing countries where there is a lack of technologically advanced ultrasound machines capable of doing sophisticated functions like fetal weight estimations but has experienced clinicians who could perform this function equally well if not better.