The placenta exerts its effects on the growth of the fetus from the be
ginning of pregnancy via metabolic and endocrine mechanisms. To achiev
e this, the placenta exchanges a wide array of nutrients, endocrine si
gnals, cytokines and growth factors with the mother and the fetus. The
se exchanges modulate or programme fetal growth and development. This
review concentrates on the function and structure of the placenta in h
umans and in animals, and the effects of experimental perturbation of
placental size and function on fetal growth. The consequences for feta
l growth of varying the abundance of peptides or, by deleting genes, i
nsulin-like growth factors or cytokines, are also described. Maternal
nutritional and hormonal state from as early as the first few days aft
er fertilization, can influence the growth rate of the placenta and th
e fetus and also the length of gestation. Influences on placental deve
lopment and their consequences will clearly have an impact on the plac
ental control of fetal growth. Variations in the maternal environment
and consequent perturbation of the metabolic and endocrine environment
of the placenta and fetus are implicated as being responsible for the
associations between prenatal growth of the placenta and its fetus an
d the subsequent risk of adult disease. The next challenge will be to
determine the dominant influences at each stage of fetal and placental
growth.