Intrauterine Growth Restriction

Currently, over 200 million children are considered to be undernourished; many of them first experience nutrient deprivation in utero and were born small compared to healthy children. Maternal diet, along with a host of other physical and environmental factors, is the primary source of energy that promotes fetal growth. Energy restriction of the mother, and ultimately the fetus, results in impaired fetal growth, manifested in intrauterine growth retardation, or restriction (IUGR). Two classifications of IUGR are currently used by healthcare professionals: symmetric is defined as less than the 10th percentile for birth weight and asymmetric defined as less than the 10th percentile for birth weight and normal head but small abdominal and muscle development. It is estimated that between 17 and 27.6 million babies born each year experience IUGR, the vast majority of whom are born in less developed or developing countries. For example, Asia, specifically India, has the highest prevalence of IUGR followed by Latin America and Africa. Still, regardless of the geographic location, causes of IUGR are universal and generally associated with inadequate delivery of nutrients to the fetus, caused by either inadequate intake by the mother or poor placental circulation.

Inadequate maternal caloric intake immediately before and during pregnancy is the primary factor predisposing a fetus to IGUR. However, in developed countries, the causes of IUGR are cigarette smoking, low weight gain during pregnancy, and low prepregnancy body mass index (BMI). In developing countries, the primary causes of IUGR include low weight gain during pregnancy and low BMI prior to pregnancy. Regardless of the level of development, a less prevalent dietary risk factor for IUGR extends to [Page 412]micronutrient deficiencies, such as low foliate, zinc, and magnesium, lending support to aid programs that promote the intake of foods rich in protein and micronutrients.

Among children born with IUGR, a percentage are born small for gestational age (SGA), defined as a birth weight for gestational age less than the 10th percentile of a healthy population, such as the United States. While maternal age, smoking, altitude, and maternal height are all factors that contribute to babies being born SGA, the main cause of SGA births is maternal undernutrition, especially in developing countries.

The timing of maternal undernutrition has important implications for future risk of chronic diseases in offspring. The relationship between when a child is exposed to IUGR and later disease risk varies by particular disease. Again, maternal undernutrition resulting in IUGR and babies born SGA occur primarily in the second and third trimester of pregnancy. Undernutrition throughout pregnancy and prior to pregnancy also increases the likelihood of IUGR occurring, a phenotype that is now believed to be a risk factor for chronic diseases in adulthood.

Maternal nutrition is essential for normal and proper growth of the fetus and placenta. It is clear that undernutrition results in reduced fetal and placental growth and that fetal growth retardation that is often permanent. Perhaps more importantly, and central to this entry, is that maternal diet during pregnancy not only has immediate effects on fetal growth, size, and development, but also that energy and/or protein deprivation in utero increases the risk for many chronic diseases in adulthood, such as Type 2 diabetes, hypertension, and other forms of cardiovascular disease.

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