Biological mechanisms of environmentally induced causes of IUGR.

The causes of intrauterine growth retardation (IUGR) are multiple, involving many different factors. Studies in humans and animals have shown that the maternal environment is the most important determinant of newborn weight, accounting for more similarity in birth weights of siblings than does genetic affinity. In addition to a direct relationship with the degree of maternal plasma volume expansion, many clinical factors are associated with IUGR. These factors include multiple gestation; fetal, genetic, and chromosomal anomalies (Down's syndrome and Turner's syndrome); infections such as TORCH syndrome (acronym for toxoplasmosis, rubella, cytomegalic disease, and herpes); and various maternal disorders including anemia, severe chronic asthma, chronic renal disease, heart disease and hypertension. Maternal stress factors, including narcotic addiction, cigarette smoking and chronic alcoholism, are associated with IUGR. Placental anomalies including hemangiomas, placental infarcts, single umbilical artery, and small placental size are also associated with intrauterine growth retardation. Poor nutritional status of the mother at conception and inadequate energy and protein intakes during pregnancy can also result in IUGR. Because IUGR children are not a homogeneous group, they have a broad spectrum of growth, health, and developmental outcomes. In general they have higher rates of subnormal growth, morbidity, and neurodevelopmental problems. The biomedical mechanisms reflected in nutritional, infection-related, hormonal, and metabolic parameters are not likely to be independent causative factors of IUGR, but important mediating factors of a pathologic process set in motion by other agents and insults. This paper focuses mainly on the possible negative effects that a deficient maternal diet might have on fetal development and growth.