Estimation ASIM BRANKO Zagreb,


of fetal weight by ultrasonic abduminometry M.D.




The fetal abdomen was measured with an ultrasonic contact scanner in order to correIute abdomenal circumference and birth weight. A sample of 134 measurements was used to calculate a standard graph, which was then tested against a subsequent 280 measurements, giving a mean estimation error of IO5 Gm. Head-to-abdomen circumference ratio measurements were used to assess the type of growth retardatiotl.

IT IS GENERALLY accepted that any method that could accurately predict fetal weight would be of considerable help in the recognition of fetal growth retardation and in the management of labor. Methods utilized so far have been based on radiography, clinical assessment, and ultrasonic cephalometry. From ultrasonic studies it would appear that attempts to predict birth weight from a single biparietal diameter measurement near term are of little value and very often are as good as estimation made from paipation of the uterus. Willocks and associates’ found that in 67 pet cent of cases the fetal weight could be estimated to within 2454 Gm., Thompson and associates’ found that in 68 per cent of cases it could be estimated to within +-480 Gm., and Kohorn3 estimated in 68 per cent of cases to within 490 Gm. From these results it was generally concluded that a single biparietal diameter reading was of value in fetal weight prediction. These figures, however, seem less impressive if we consider the statement by Lindf that, if an observer did not examine the patient at all, but simply guessed each fetal weight as 3.3 kilograms, he would be within 454 Gm. of the true weight in 70 per cent of 500 normal cases at term. From this it is clear that, to assess the value of any method of fetal weight prediction, it is important to include in the study the babies at the upper and lower limits of normal. In none of the previously mentioned ultrasonic studies was there a significant number of babies below 2.5 kilograms. Recently Campbell? in a

series which included 2 11 babies bekrw 2.5 kilograms, found that birth weight could be predicted to within 406 Gm. in 68 per cent of cases. In our series ot~2,684 babies (201 of low birth weight) we could predict the weight to within 420 Gm.6 At the extremes this represents an improvement compared to predictions made from abdominal palpation but in practical terms it is not acceptable. Clearly, ultrasonic cephalometrv is inadequate for weight prediction. Another technique is required that can predict birth weight from a single measurement during the last 4 weeks of pregnancy but not more than 2 days before birth. The present study was undertaken to assess the degree of reliability of estimation of fetal weight by ultrasonic measurement of the fetal abdomen circumference at the level where the umbilical vein crossenters the liver.

Mabriats and methods A total of 280 patients with singleton pregnancies were examined. Only measurements made within 2 days of delivery were included in order to avoid significant discrepancy due to growth of the fetus in the The interval between measurement and delivery. machine used was a Diasonograph NE 4102, with the ultrasonic caliper speed set to 1,600 m. per second. The technique of fetal abdominometry involves a serial longitudinal scan in order to determine the correct level and angle for performance of a circum: ference measurement of the fetal abdomen. ‘The angle of inclination of the cross-sectional plane is generally taken at right angles to the long axis of the fetus. The aparatus is then changed to a transversed (Fig. I) position, tilted to the previously measured angle, and cross-sectional scans are done until the umbilical vein is identified, passing through the liver. In a narmal vertex position this is relatively easily found. 1.n a

From the Department of Obstetrics and Gynaecobgy, Medical Faculty, University of Zagreb. Accepted JamaT

20, 1976.


requests: Dr. Bra& Breyer, University Gynaecological Hospital, Petrova 13. 4 1000 Zagreb, Yugoslavia. 962

Volume Number

125 I

Fig. 1. Transverse section of the fetal abdomen and the umbilical vein (XV.) surrounded by the speckling from the fetal liver.

Fetal weight estimation by ultrasonic abdominometry


Fig. 2. Circumference measurement using the longest and the shortest diameter of the cross-section. C = (d, + d2) n/2 = (d, + dz) x 1.57.

breech or transverse position the right plane is much harder to find. It requires an experienced operator or it can be a source of error. Circumference measurements are performed from the largest possible image on the screen. As can be seen from Fig. 2, we measure two diameters (the largest and the smallest) and calculate the circumference, i.e. we approximate the circumference by an ellipse. The two diameters are usually measured directly from the screen with the bright-up calipers. Stimulated by the investigations of Campbell’ and Hollander,‘6 we performed measurements of the headto-abdomen circumference ratio, measuring the head circumference at the normal BPD measurement level in the same manner as the abdomen circumference.



Results In the first part of our study we plotted 134 circumference measurements against actual birth weight. In Fig. 3 the dependence of our circumference measurements on birth weight is shown. Only measurements performed within 2 days of delivery were used. The circumference in the graph is the circumference of the fetal abdomen as previously described. In a subsequent 280 measurements we checked the graph in Fig. 3 by taking the mean value from the graph as the expected weight and calculating the error of the prediction as the difference between our prediction and the actual weight. The results are given in Table I. In 830 of the cases the difference between the actual and expected weight was within +- 150 Cm. and in 94 per cent within2250 Cm. The mean error was 105 Gm. and the maximum error 310 Gm. The prediction of birth weight was as proficient at the extremes of birth










Fig. 3. Graphic representation of the dependence of abdominal circumference of the fetus on weight at delivery during the last 4 weeks of gestation. The graph was calculated from 134 cases measured within 2 days from delivery. weight range as in the middle. Among the whole set there was one odd result, producing an error of 620 Gm. It was a breech presentation and by postpartal measurement the ultrasonic measurement result was proved to be an obvious error and in view of the


Kutjak and Breyer

Table I. Difference


actual and expected

weights* O~@krence


2 50

*50to? 100 37 100 to * 150 +- 150 to 2 200 2 200 to r 250

over 250 Total

No. of pati.t?nts 42 106 84 30 13 5 280

*Mean error = 105 Cm.; maximum error

Fig. 4. Echograms showing head (above) and abdomen (below) at 37 weeks of menstrual age. The abdomen circumference is now slightly larger than that of the head and will continue to increase in relation to the head circumference toward term (WV. = umbilical vein).

homogenity of the rest of the results this one was discarded. The fetal weights ranged from 1,300 to 4,850 Gm. After the abdomen circumference measurement started to show its value we undertook 200 measurements of head-to-abdomen circumference ratio. During the second trimester this ratio is greater than one but by 36 to 37 weeks, because of the rapid accumulation of subcutaneous fat and soft tissue during the later part of pregnancy, the circumference of the abdomen has caught up with that of the head (Fig. 4), and during the last 4 weeks it is almost invariably greater. However, in most cases of growth retardation this reversal of the head-to-abdomen circumference ratio does not occur and in Fig. 5 it can be seen that 18 out of 19 babies born below the tenth percentile weight for gestation had ratios of one or greater; conversely, 177 out of 181 babies of normal weight (97.5 per cent) had ratios of less than one.

Per cent 1.5 38 30 11 4.i I.3

100 = 310 Gm.

The decision to induce labor before term in complications of pregnancy is to a certain extent influenced by the assessment of fetal size. In cases where the weight of the baby is about 2,000 Gm. errors of more than 400 to 500 Gm. may critically affect the baby’s chances for survival if a wrong decision is made. In the same wa) any method that provides reliable information on fetal size and which can be used to screen large number of patients will be a potent factor in the reduction of. perinatal death and morbidity. Despite the fact that the biparietal diameter is the most accurate linear measurement that can be obtained during the antenatal period, cephalometry is not particularly helpful in estimating fetal weight. Many workers have attempted to make predictions of the birthweight by palpation of the maternal abdomen, because clinical estimation after abdominal palpation is the commonest method of assessing fetal weight in utero. Loeffler’ found that 79.9 per cent of estimates were within 1 pound of the baby’s weight. Johnson and Tosach” calculated fetal weight from the distance between symphysis pubis and uterine fundus and the station of the fetal head. ‘l‘he) reported an accuracy of +-240 Gm. in 50.5 per cent of 200 examined cases. Poulos and Langstadt” estimated fetal weight according to the volume of ut.erus with an accuracy of 1250 Gm. in 68 per cent of estimations. Their material consisted of 45 cases with ncp babies below 2,500 Gm. More recently 0ng and Sen” estimated in 82.5 per cent of cases within t 1 pound but there was a tendency to overestimate in the lower range and underestimate in the higher range. The work of Beazley and Kurjak” shows a prediction of fetal weight after 36 weeks’ gestation to within -t-500 Gm. in 75 per cent of cases. Prediction of birth weight by ultrasonic measurement of fetal body sections was recommended by Thompson and associates,” Garret and Kobins0n.l’ Hansmann and associates,13 and Campbell.” Thompson and associates,’ using a contact scanner, took sections of the fetal thorax and by means of a

Volume Number

Fetal weight estimation by ultrasonic abdominometty




Fig. 5. Relationship between the head-to-abdomen groups in 200 cases measured on 2 days prior

formula based on the maximum and minimum measurements were able to predict the fetal weight within 1500 Gm. of the actual weight in 80 per cent of babies. Hansmann and associatesr3 took circumference measurements of the fetal thorax at right angles to the long axis of the fetus. We followed Campbell’sr4 suggestion of taking a lower level across the upper fetal abdomen on the level of umbilical vein. As the fetal liver is the most severely affected organ in cases of type II growth retardationI we also feel that this section is of greater importance in the assessment of fetal nutrition. The fetal abdomen-to-head circumference ratio could be a valuable means of assessing fetal nutrition in late pregnancy and in addition may provide a simple

REFERENCES 1. Willocks, J., Donald, I., Duggan, T. G., and Day, N.: J. Obstet. Gyanecol. Br. Commonw. 71: 11, 1964. 2. Thompson, H. E., Holmes, J. H., Gottesfeld, K. R., and Taylor, B. S.: AM. J. OBSTET. GYNECOL. 92: 44, 1965. 3. Kohorn, E. 1.: AM. J. OBSTET. GYNECOL. 97: 553, 1967. 4. Lind, T.: Br. J. Hosp, Med. 3: 501, 1970. 5. Campbell, S.: Clin. Obstet. Gynaecol. 1: 41, 1974. 6. Kurjak, A., DraZan%, A., OlajoS, I., Latin, V., and Breyer, B.: Second european Congress on Ultrasonics in Medicine, Book of abstracts, Munich, 1975, p. 88. 7. Loeffler, F. E.,: J. Obstet. Gynaecol. Br. Commonw. 74: 675, 1967. 8. Johnson, R. W., and Tosach, C. E.: AM. J. OBSTET. GYNECOL. 68: 891, 1954.

circumference ratio and the birth weight centile to induction of labor or elective cesarean section.

method of distinguishing between wasted and stunted growth-retarded babies. Finally, we believe that for detection of a small-fordates fetus from a single ultrasonic examination in late pregnancy the fetal abdomen circumference measurement could be a method of choice. It is our practice to perform this measurement in the majority of patients undergoing induction of labor or elective cesarean section. The cooperation of Dr. I. OlajoS and helpful criticism of Dr. V. GoreEan are kindly acknowledged. We are grateful for the encouragement of Prof. B. Rajhvajn.

9. Poulos,

P. P., and Langstadt, J. R.: AM. J. OBSTET. 65: 233, 1953. Ong, H. C., and Sen, D. K.: AM. J. OBSTET. GYNECOL. 112: 877, 1972. Beazley, J. M., and Kurjak, A.: Nursing Times, June 14: 23, 1973. Garret, W. J., and Robinson, D. E.: Obstet. Gynecol. 38: 525, 1971. Hansmann, M., Voight, U., and Baeker, H.: Arch Gynakol 414: 194, 1973. Campbell, S.: Clin. Perinatol. 1: 507, 1974. Rosso, P., and Winick, M.: J. Perinat. Med. 2: 147, 1974. HollZnder, H. J.: Die Ultraschall-Diagnostik in der Schwangerschaft (2. Auflage), Muenchen-Berlin-Wien, 1975, Urban und Schwarzenberg. GYNECOL.

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Estimation of fetal weighty by ultrasonic abdominometry.

Estimation ASIM BRANKO Zagreb, KURJAK, of fetal weight by ultrasonic abduminometry M.D. BREYER, PH.D. Yugoslavia The fetal abdomen was measured...
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