Paper - Two simple nomographs for estimating the age and some of the major external dimensions of the human fetus

Two Simple Nomographs For Estimating The Age And Some Of The Major External Dimensions Of The Human Fetus

Richard E. Scammon

The Graduate School and Institute of Child Welfare, University of Minnesota

TWO FIGURES

It has been known since the days of Mall’s classic studies (’07) that linear and circumferential dimensions of the body could be Very generally expressed by a straight line, viz:

D=aL+b (1)

Where D is the dimension in question, L is the body length, either total or crown—heel length or crown—rump length or sitting height, and a and b are empirically determined constants. This rule holds true for practically all external bodily dimensions from the middle of the third lunar (or menstrual) month of prenatal life to birth. The age can also be determined approximately from the total or crown—heel body length by the simple parabola:

A = ".3 + 0.089 CH + 0.00128(_CH)“ (2)

where A is the age in lunar months from the onset of the last menstruation and CH is crown—heel or total body length. If estimates of age (A) from the crown—rump (CR) length or sitting height of the body are preferred, the following expression obtained by substitution in (2) may be used:

A = 1.7 + 0.106 CR + 0.00293(CR)” (3)

The expressions given should be regarded as approximations at best, due in large part to the inaccuracy of even the best collections of records of duration of pregnancy. More complicated expressions will give slightly better fits and will extend below the second half of the third lunar month.

221

THE ANATOMICAL RECORD, VOL. 68, NO. 2 222 RICHARD E. SCAMMON

VII

Gntero-posterior diameter at nipples “

Fig. 1 Nomograph of ten major external bodily dimensions in the fetal period, of crownheel length, crown-rump length, and computed age. CH, crown-heel, total or standing height (length), CR, crown-rump, body stem or sitting height (length). Numbers on the vertical scales in centimeters (Arabic numerals), with the exception of computed age (from the first day of the last menstruation) which is given for lunar months in Roman numerals. NOMOGRAPHS FOR FETAL AGE AND DIMENSIONS 223

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m°°\“" CR H lntercristal diameter

Length of lower extremity X ' 55 Forearm length 270 I ' ‘ do-as Thngh l¢ng1‘h(1'rochant'er 1-o knee) IX 5 105 Pool‘ length

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I fifdl VIII Q5 23 I monfhs 22. x 9 I 270 | * as 55 21 we’ v11 3 . IX 15 20 5 15 1 19 v1 14 « § . 5 15 V111 13 , . 7 17 12 65 16 v11 V 11 ' . 6 15 1o ' 5.5 14 V1 1v 9 5 4 1 9 4.5 13 7 4 W25 V 5 10

2 6

5 2 6 Length of upper exrremirq 1'5 5 arm lengfb 1 4. 1 Hand Iengfh ~ Leg length 5

Spine length 5 Fig. 2 A second nomograph of external bodily dimensions. Details as described in figure 1.

1 1 ND 9! 0' an ‘.0 I 224 RICHARD E. SCAMMON

Using the expression (2) for the relation between total body length and age (developed by Scammon and Calkins, ’23) and the several expressions for the relation of external bodily dimensions to crown—heel or to crown-rump length (Calkins and Scammon, ’25; Scammon and Calkins, ’29), to eliminate tedious computation two nomographs‘ have been drawn up to give the approximate size of commonly measured external dimensions with respect to crown-heel and crownrump body length and computed menstrual age.

The construction of the nomographs is simple. They consist of oblique grids (so arranged to give more space for lettering). These oblique grids contain vertical and oblique lines. The lateral vertical lines on either side are calibrated for crown-heel and crown—rump length and external to these are columns in alternate segments black and white representing the calculated age in weeks from the first day of the last menstruation. The calculated age in lunar months is indicated on these columns in Roman numerals. Each intermediate vertical line is sealed for the dimension in question. The oblique lines represent 5 cm. intervals of total body length.

The nomographs may be used in several ways. If the magnitude of a mean approximate dimension or dimensions is desired for a given age, draw a taut thread across the nomograph between the corresponding age points and parallel to the oblique lines on the grid. If an estimated age or dimension is desired from a given dimension, use the same process, placing the thread at the level of the measurement on the appropriate scale and keeping it parallel to the oblique lines of the grid.

‘The principles of nomography were suggested in the seventeenth century. The subject was really developed by M. d’Ocagne (1884). Nomographs are used chiefly for representing power expressions. Perhaps the best discussion of nomographs in M. d’0cagne’s Traité dc Nomographie (Paris: G. Villars, 1899) and Le calcul simplifié (Paris, ’05). Good accounts in English are given in Brodetsky, S., A first course in nomography (London: G. Bell and Sons, ’20), Lipka, J., Graphical and mechanical computation (New York: John Wiley and Sons, '18), and Feldman, W. M., Biomathematics (London: Charles Griffith and C0,, ’35). The nomograph is rarely used for rectilinear functions. NOMOGRAPHS FOR FETAL AGE AND DIMENSIONS 225

LITERATURE CITED

CALKINS, L. A. AND R. E. SCAMMON 1925 Empirical formulae for the proportionate growth of the human fetus. Proc. Soc. Exp. Biol. and Med., vol. 22, pp. 353-357. MALL, F. P. 1907 On measuring human embryos. Anat. Rec., vol. 1, pp. 129-140. SCAMMON, R. E. AND L. A. OALKINS 1923 Simple empirical formulae for expressing the lineal growth of the human fetus. Proc. Soc. Exp. Biol. and Med., vol. 20, pp. 353-356. 1929 The development and growth of the external dimensions of the human body in the fetal period. Minneapolis: The University of Minnesota Press.