(1)
Department of Family Medicine, University of California, Riverside, Riverside, CA, USA
Key Points
1.
Growth and development represent a complex interaction between genetic predisposition and environmental exposure.
2.
Screening for genetic risk factors ideally begins in the preconception period.
Background
Most fetuses are free from identifiable genetic abnormalities. Their pattern of growth and development falls within the range of normal parameters. Under some circumstances physical growth is restricted (intrauterine growth restriction). This is discussed in Chap. 6. Under other circumstances, however, genetic abnormalities lead to abnormalities in growth, development, or both. These abnormalities may be relatively minor (e.g., color blindness) or they might be more significant (e.g., muscular dystrophy). Primary care providers must be familiar with common abnormalities and available screening options to identify these conditions when they arise.
Genetic inheritance is a complex interaction of maternal and paternal genotypic predisposition with a variety of environmental factors. The resulting phenotypic expression represents final outcome of these two factors. A review of both familial genetic predisposition and environmental risk factors will allow providers to discuss with expectant parents the developmental risks, if any, associated with a particular pregnancy.
Chromosomal abnormalities fall within two major groups, abnormalities of chromosomal number (e.g., trisomy 21, Down syndrome) and abnormalities of chromosomal structure (e.g., hemophilia). Chromosomal abnormalities (genotypes) may have variable phenotypes. This variability can represent variable expressivity (variation in expression of a disease within a population with a specified genetic abnormality) and/or variable penetrance (likelihood of expression within an individual with a genetic abnormality).
History
Ideally genetic screening by history would begin in the preconception period. If that is not possible, it should begin as early in the prenatal period as possible. A variety of standardized screening tools exist to assist providers with the evaluation of maternal and paternal genetic risk factors. Table 5.1 provides a selected list of conditions commonly screened for in pregnancy. Common medical conditions with a strong genetic predisposition should be reviewed, including congenital abnormalities, cystic fibrosis, Down syndrome, hemophilia, sickle cell disease, neural tube defects, Tay–Sachs disease, and muscular dystrophy, among others. Although these standardized screening tools are helpful as a starting point, providers should be aware that additional detail may be required for some high-risk patients. If the primary care provider does not feel adequately prepared to complete such a genetic screening, referral should be made to a genetics counselor or a maternal–fetal medicine specialist.
Table 5.1
Selected congenital conditions screened for in preconception/prenatal care
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