Small as Fetus and Short as Child: From Endogenous to Exogenous Growth Hormone¹

IN THE human species, the fastest enlargement of body size occurs during the last trimester of fetal life, despite the constraints imposed by the maternal environment (1). The first major act in the drama of human growth is played out by term birth, which is partly timed by the fetal pituitary (2). Even so, much growth potential is left at birth, and a great deal of it is used during the first postnatal years (3). There is a persistent principle in physiology that the faster a growth process is occurring, the more responsive (hence, in the negative sense, vulnerable) it is to forces impinging on it (3). As prenatal growth is more rapid than at any subsequent time, it is also one of the most vulnerable phases. If growth-limiting factors are prenatally exerted in a pronounced or prolonged fashion, they may not only result in substantial growth retardation at birth, but also in a persistent delay or reduction of postnatal growth, as well as in other long term consequences on cogni-tive, endocrine, metabolic, and cardiovascular functions (4–6).