A teratogen is any substance that can cause developmental abnormalities in a fetus following exposure during pregnancy. The discovery of teratogens often follows an observed increase in the prevalence of specific birth defects. A tragic example is thalidomide, a drug used in the early 1960s to treat morning sickness. Fetal exposure during early development resulted in phocomelia, a condition characterized by shortened or absent limbs, with hands and feet attached close to the body.
Teratogens are diverse and can be found in various environments, including homes and workplaces. Their effects depend on the specific agent, dosage, duration, and timing of exposure. The first trimester of pregnancy is typically the most vulnerable period for fetal development. These agents encompass a wide range of categories.
- Infectious agents (e.g., rubella, cytomegalovirus, varicella, herpes simplex, toxoplasma, syphilis).
- Physical agents (e.g., ionizing radiation, hyperthermia).
- Maternal health factors (e.g., diabetes, maternal phenylketonuria (PKU)).
- Environmental chemicals (e.g., organic mercury compounds, polychlorinated biphenyls (PCBs), herbicides, industrial solvents).
- Drugs (prescription, over-the-counter, and recreational).
Generally, when medication is necessary during pregnancy, the lowest effective dose should be used, and combination drug therapies and first-trimester exposures should be avoided whenever possible.
The type and severity of abnormalities resulting from teratogenic exposure also depend on the genetic susceptibility of both the mother and the fetus. For instance, variations in maternal drug metabolism influence the metabolites to which the fetus is exposed and the duration of that exposure. The fetus’s genetic predisposition to a particular teratogen also affects the outcome.
Preventable Teratogens: Alcohol and Smoking
Alcohol and smoking are two leading preventable causes of birth defects and developmental disabilities. Alcohol consumption during pregnancy has significant consequences for the fetus and the baby. Alcohol crosses the placenta from the mother’s bloodstream to the fetus. Because alcohol is metabolized more slowly in a fetus than in an adult, alcohol levels tend to remain elevated for longer periods in the baby’s system. Birth defects associated with prenatal alcohol exposure can occur as early as the first three to eight weeks of pregnancy, often before a woman realizes she is pregnant.
Fetal alcohol syndrome (FAS) is a spectrum of abnormalities in infants born to mothers who consumed alcohol during pregnancy. It is the most prevalent known non-genetic cause of intellectual disability in the U.S.
In 2001, approximately 11.4% of U.S. women smoked during pregnancy, with rates ranging from 3.9% in DC to 26.2% in West Virginia. Smoking nearly doubles a woman’s risk of having a low birth weight baby due to impaired growth before birth, preterm delivery, or a combination of both. Premature and low birth weight infants face increased risks of serious health problems during the newborn period, chronic lifelong disabilities (e.g., cerebral palsy, intellectual disability), and possibly death. Recent studies suggest a possible link between prenatal smoking exposure and behavioral problems in later childhood and adolescence.
Illicit Drug Use During Pregnancy
Approximately three percent of pregnant women use illicit drugs like marijuana, cocaine, Ecstasy and other amphetamines, and heroin. These drugs can lead to low birth weight, withdrawal symptoms, birth defects, or learning and behavioral problems.
Conclusion
Understanding what a teratogen is and the potential risks associated with exposure is crucial for ensuring a healthy pregnancy and the well-being of the developing fetus. Avoiding known teratogens, especially alcohol, tobacco, and illicit drugs, is vital, as is consulting with healthcare professionals regarding medication use during pregnancy.
