Factors Influencing Fetal Growth

Abstract

After completing this article, readers should be able to: 1. Describe the roles of insulin-like growth factor on fetal growth and development. 2. Delineate components of “maternal constraint.” 3. Explain the role of the placenta in regulating fetal growth. 4. Describe the effects of fetal glucose, amino acid, and fat supply on fetal growth. The principal determinants of fetal growth are fetal genotype and in utero environment. Environmental factors include maternal and paternal genetics, maternal size, and the capacity of the placenta to provide nutrients to the fetus. These environmental factors interact with the intrinsic growth pattern of the fetus, yielding a particular rate and composition of fetal growth. Most of the variation in fetal growth in a population is due to variations in environmental factors, not the fetal genome, although a genetically abnormal fetus clearly might not grow as well as a normal fetus if affected genes include those that are important for growth. Many genes contribute to fetal growth and birthweight. Techniques in which specific genes can either be deleted (“knockouts”) or overexpressed have led to greater understanding of how some of these genes regulate fetal growth. Such studies have shown that both maternal and paternal influences are present during fetal development and are passed on to the developing fetus by spermatozoa or oogonia by a mechanism called imprinting. Although the maternal genetic composition exerts greater influence than fetal genotype in the overall regulation of fetal growth, both maternal and paternal genomes are important in fetal growth and development (1)(2). For example, gynogenetic zygotes (two maternal genome copies) lead to underdeveloped extraembryonic tissues but well-developed embryos. The more modest regulation offered by the paternal genotype is essential for trophoblast development. For example, zygote nuclear transfer experiments have shown that androgenetic zygotes (two paternal genome copies) develop extensive trophoblast tissues but …