Timing of first appearance and subsequent distribution of adipose tissue were assessed in 488 normal-for-age human fetuses. The sample represented each of the three trimesters of normal pregnancies. Light microscopy showed that adipose tissue first appears and progressively develops from the 14th to 24th week of gestation (100-216 mm crown-rump length) in those areas where it characteristically accumulates after birth. No significant sex differences were found in patterns of early fat deposition. It is suggested that the second trimester of gestation is the critical or key period in fat adipogenesis.

As shown in 56 human embryos and fetuses between 15 and 104 mm in crown-rump length, "adult" metacarpal-phalangeal length rankings are attained by the seventh intrauterine week and near-adult bone-to-bone ratios or proportions by the theirteenth week. Micrometric measurements of optically-projected histological hand sections show relative elongation of the distals between the 15-29 mm and 30-44 mm crown-rump range, and relative reduction to radiogrammetrically-determined adult proportions by the 90-104 mm CRL.

805 normal-for-age human embryos and fetuses were used to study early prenatal fat development. The investigation included observations on stages of fat morphogenesis at the light microscopic level and computerized image analyses of fat lobule size and number. The buccal fat pad was selected as a model system for the analyses. Fat tissue differentiates between the 14th and the 16th weeks: there are five morphogenic phases in adipose tissue formation, strongly associated with the formation of blood vessels. Fat lobules are the earliest structures to be identified before typical vacuolated fat cells appear. Concerning fat lobule size and number, we show that after the 23rd week the total number of fat lobules remains approximately constant, while from the 23rd to 29th week the growth of adipose tissue is determined mainly by an increase in size of the lobules. These results suggest that the 14th through the 23rd week is a sensitive period in fat lobule development, and that disturbances of normal adipogenesis during this period may play a role in the etiology of obesity in later life.

No abstract

This study was designed to demonstrate quantitative growth trends in the human upper face region before birth. Photographs of 68 sagittally sectioned fetal heads were measured using a series of linear and angular measurements for changing height, length and shape. Cross-sectional types of data were treated with a statistical model which tested for linearity of the data, correlation between growth changes and increasing fetal age, significance of the differences between rates of change in related upper face regions and the general significance of the trends shown in the study.Pooled data for the second and third trimesters suggested three distinct growth trends. Linear measurements of the cranial base, nasal area, and palate correlated significantly with increasing crown-rump length. Finally, a composite upper face profile for the sample suggested a relative migration of the region downward and forward away from the anterior cranial base and the hypophyseal fossa. These three trends collectively demonstrated that the pattern of upper facial growth before birth involves progressive enlargement of a relatively static profile. It should be understood that this pattern is a group trend as shown by cross-sectional sampling of many individuals over a period of time with no individual being measured more than once, Conversely, variabilities in a specific individual's growth are most appropriately demonstrated by measuring that individual several times throughout some time span, i.e., by longitudinal sampling. Studies of the human fetus are restricted generally to the cross-sectional sampling technique.The close similarity of these prenatal trends with those reported for postnatal craniofacial growth suggests that certain patterns of facial growth in childhood can be seen as early as the beginning of the fetal period and emphasizes the continuum of human development.