58 FIELDS, GRAPHS, AND OTHER DATA ON FETAL GROWTH. 



The average duration of pregnancy (as reckoned from the beginning of the last men- 

 strual period, in all cases, with a duration of 236 to 329 days) was 279.8 days in the case of 

 1,186 Caucasians and 276.9 days in the case of 1,181 negroes. These averages agree very 

 well with the story of the charts, although they are, of course, too low for full-term averages. 

 Since the average duration of pregnancy for mature fetuses, as counted from the date of 

 coitus, in a total of 2,578 cases reported by Ahlfeld, 1869 and 1871, Schlichting, Issmer, 

 1889, and Inouye, 1912, and those of Lowenhardt as well, was 269.19 days, a somewhat 

 lower average duration than the normal could be expected in the series of cases con- 

 cerned here. As will be seen later, the comparatively high average duration never- 

 theless obtained, which so closely approximates the normal, has undoubtedly resulted from 

 the inclusion of histories with an erroneously long duration. 



The average weight of 1,026 females with a duration of 236 to 320 days was 3,242.3 

 grams and that of 1,033 males was 3,387.4 grams, while that of 1,031 whites and 1,027 

 negroes was 3,436.5 and 3,185.4 grams respectively. The average length of the Caucasians 

 falling in this period was 49.8 cm., that of the negroes 48.5 cm., and that of the females of 

 both races was 48.7 cm. as compared to 49.6 cm. for the males. 



The average weight of 1,146 males of both races of all ages as plotted was 3,258.4, and 

 that of 1,161 females was 3,197.6 grams; although below the preceding averages (as would 

 be expected) it is evident that both these averages are only slightly below the normal aver- 

 ages for the sexes as reported from some European clinics, in spite of the fact that my 

 statistics include fetuses from 180 days on and that approximately half of them are negroes. 

 Zangenmeister (1911) reports the average weight for 11,181 collected European cases as 

 3,242.49 grams and their average length as 49.93 cm. The average weight of all plotted 

 cases of both sexes and races in this series was 3,228 grams. However, the averages for 

 length for these plotted cases of all ages, which are 48.1 cm. for the males and 47.1 for the 

 females of both races, are manifestly somewhat lower in comparison with the weight 

 averages. It is interesting to observe that the differences between the average weight of 

 the sexes in the charted cases of all ages is only 60.8 grams, although the difference in 

 length is 1 cm., or fully equivalent to the sexual differences at birth. These Weissenberg 

 (1911) gave as 0.8 cm., while Stratz (1909) regarded them as practically non-existent, and 

 later (in 1910) as quite insignificant, in spite of the fact that he reported (1909) a sexual 

 difference in natal weight of 250 grams as obtained from 400 cases. This sexual weight- 

 difference far exceeds that of the usual European statistics. 



From a comparison of these figures it is evident that the difference between the average 

 weights of the sexes rises from 60.8+ to 157.1 grams merely by the exclusion of all cases 

 with a duration of less than 236 days, and similarly, that the differences in average length 

 rises from 1.0+ to 1.6+ cm. Moreover, it is also evident that the percentage sexual differ- 

 ences in both length and weight increase with advancing maturity, as might be expected. 

 Although I regret exceedingly that the data at hand did not enable me to determine 

 how early these sexual differences are recognizable and when the greatest percentage sexual 

 differences occur, yet it may be quite safely inferred, I think, that sexual differences in 

 weight probably appear earlier than sexual differences in length. It would also be interest- 

 ing to learn whether the advent of these differences can be correlated in any way — as seems 

 probable — with special developmental changes in the ovaries and testis after the manner 

 of the later adolescent differences and changes. However, the observation of Fesser (1873) 

 that males are 77 grams heavier in the ninth than in the eighth month and that females are 

 heavier in the eighth month, as well as the similar but somewhat contrary conclusions of 

 Hecker, probably rest on too small and hence on a misleading basis. 



