The timing factor in the pathophysiology of the intrauterine growth retardation syndrome.

Three different types of intrauterine growth retardation can be identified depending on the moment at which supplies to the fetus are diminished. When a reduction in sustenance occurs early in the first trimester of pregnancy, a well-proportioned but growth-retarded baby may be expected. When the negative factors develop around the 30th week of pregnancy, the result is a disproportionately growth-retarded infant. Both types of retardation can be illustrated using longitudinal uterine height and biparietal diameter values and by neonatal anthropometry. Epidemiological examples exist defining factors which produce these two kinds of retardation. The third type occurs when a reduction in food supplies takes place in the last month of pregnancy and causes a depletion of the fetal fat stored. Weight retardation is observed with little or no height impairment. In planning public health activities such as nutrition interventions for developing countries, the type of intrauterine growth retardation present in the target population should be considered in order to determine which type of intervention would be most appropriate, and establish its correct timing.