Early intrauterine development: II. The rate of growth in Black and Central American populations between 10 and 20 weeks' gestation.

The application of the growth-rate standards, extablished for Caucasian embryos and fetuses in a previous report, to Black and Central American racial groups has been investigated. Comparison between menstrual age and crown-to-rump length indicated differences in the 10 to 15 weeks' gestation range. However, growth rates for the same groups were practically identical between the 15th and 20th weeks of pregnancy. This finding suggests that the actual rate of growth is closely similar in the respective ethnic groups and that apparent discrepancies reflect erroneous, or purposefully false, menstrual histories rather than dissimilar growth patterns. Largely identical rates of development were suggested by the crown-rump length to foot length to body weight interrelations among the various racial groups. A moderate, but rather predictable, deviation from the earlier established standards was noted in the crown-rump length versus foot length ratios of Black American fetuses, providing the only exception to what appears to be a practically identical rate of growth for the investigated ethnic groups in the first half of gestation. The evaluation of the results was extended to involve the effect of educational and social factors on currently available data of embryonic and fetal growth. It is suggested that heretofore unconsidered factors may affect the validity of widely quoted standards of intrauterine growth.