The relationship between mammalian foetal weight and conception age

Abstract

Sheep foetal weight and length data have been collected for the purpose of checking foetal age and in the course of this work it has been found that the cube root of the foetal weight gave a linear plot with age from the 50th day of pregnancy to full term. The purpose of this paper is to describe this result and to indicate how the cube root relationship may be extended to other mammalian data, and to discuss its significance in comparative foetal physiology.Early attempts to find empirical formulae relating foetal weights to age from conception have been extensively reviewed by Needham (1931). The majority of these involved a linear relationship between weight and a power (approximately the third power) of the time or, alternatively, a relation between time and a cube or higher root of the foetal weight.Greater precision was brought to such formulae by McDowell, Allen & McDowell (1927) who introduced the concept of embryo age and obtained a formula, essentially of the power type, relating log weight and log embryo age. The embryo age was arbitrarily determined to commence with the appearance of the primitive streak (7.2 days for mouse embryos, 12 days for guinea-pigs), and the powers obtained varied from 3-65 to 3-99 for the mouse and guineapig respectively.The power obtained in this way is very sensitive to small changes in the arbitrarily fixed zero embryo age which has no sound physiological basis.If a steady state of growth exists during foetal development one would expect it to be most free from complications when the foetus has the environmental stability such as provided by an established placental circulation. It would be an advantage therefore if weight and age data for the last half or two-thirds of pregnancy could be represented without using the arbitrary expedients necessary with logarithms.This problem faced us in our endeavour to obtain a representation of collected data of weights and lengths of foetuses from Welsh ewes, which could be used for checking foetal ages.

Determination of time of conception of fallow deer in a Hungarian free range habitat

“…By substituting the results of these calculations into the formula of Huggett & Widass (1951) and taking into consideration the body weight of embryos at any given stage we calculated the number of days elapsed from the time of conception. We also incorporated our calculated hypothetical time of zero size value (t 0 = 33 days) and the calculated growth constant value (a = male: 0.0862, female: 0.0839).…”

“…In placental mammals there is an almost linear relationship between the cube root of embryonic body weight (W) and elapsed time from fertilization (T). This relationship exists from the moment of conception until the birth of the embryo T = (W 1/3 /a) + t 0 (Huggett & Widass 1951), where "a" -growth constant and "t 0 " -hypothetical time of zero size. The above relationship was proven true for several cervids such as for the American elk (Cervus canadensis) (Morrison et al 1959), and for red deer (Cervus elaphus) (Mitchell & Lincoln 1973, Sugár & Horn 1986, Szabó 2001.…”

“…2) where the origin of our lines was plotted at the already established value of "t 0 "; while, the birth weights for each sex (male: 5.0 ± 0.5, female: 4.6 ± 0.5) specific to a 231.5 day gestational period was based on data reported by Birgersson & Ekvall (1997). Thus we were able to determine the coefficient for "x" as the slope of the plotted lines of the two sexes which corresponds to the value of "a" in Huggett & Widass' (1951) equation . Based on these values and our own observations (fetal birth weight and sexes), we were able to specify the typical fertilization dates of fallow deer; and to determine whether there are any significant differences between fertilization dates of does versus yearlings.…”

Development of Connective Tissue Fibres in Pancreas of Prenatal Stages of Goat (Capra hircus)

“…Immediately, after collection each foeti was measured for its crown rump length (CRL) in centimeters with the help of nylon tape as per the technique described by . The approximate age of foeti was estimated by using the formula derived by Singh et al, (1979) in goat after interpolation of formula of Hugget and Widdas (1951) in mammals. The foeti were divided into three groups on the basis increasing gestational age (Table 1).…”

Effects of terbutaline on the fetal lamb during maternal oxytocin-induced uterine contractions

“…In seven investigations terbutaline was infiised directly into the fetal jugular vein at a rate of 0.4-10 ^g/kg/min for 20 minutes to examine fetal cardiovascular and acid-base responses. Fetal weight at the time of infusion was estimated according to gestational age [14,19], and the fetus was sacrified within 3 days of the final phase of the study. Maternal and fetal blood pressures, heart rates, andintraamniotic pressure were monitored throughout the study and were recorded on a multichannel polygraph.…”