Surface Area and Age in Prenatal Life

Abstract

In a preceding paper we have given a series of empirical formulae for the relation between the surface area and some of the major dimensions of the human body in prenatal life. These formulae are as follows:

S = 0.2808L_ch ^2,278 (1)

S = 0.4545L_cr ^2,401 (2)

S = 5.188W^0,750 (3)

In these expressions S is the surface area of the body in square centimeters, L_ch is the total or crown heel length in centimeters, L_cr is the sitting height or crown rump length, and W is body weight in grams.

The increase in surface area with respect to age in the fetal period may be estimated by the substitution of expressions for time in terms of body length or body weight in this period. We have done this using the empirical formulae of Scammon and Calkins. 1 , 2 In these expressions age is given in lunar months (of 28 days) dated from the first day of the last menstruation. These expressions only hold for the fetal period proper (from 3 lunar months to birth).

The accompanying table gives the calculated values for the surface area of the body at each month of the fetal period, as computed through crown heel length, through crown rump length and through body weight. The agreement of these figures is quite close —particularly for crown rump length and body weight, with the exception of the values at 3 lunar months.

We have also calculated the velocity, the relative or percentage velocity and the acceleration of areal growth in this period (as estimated through crown heel length). These values are shown in the last 3 columns of the table. The accompanying figure shows the results of these computations in graphic form.