Final answer:
Substances including alcohol, cigarette smoke, drugs, and certain medications can cross the placenta and harm the developing fetus. Teratogens lead to adverse effects, especially if exposure occurs during critical periods of fetal development. Pregnant individuals must manage exposure to these harmful substances to prevent conditions like FASD.
Step-by-step explanation:
During pregnancy, many substances can cross the placenta and affect the developing offspring. Teratogens are environmental agents, including biological, chemical, or physical factors, that cause damage to a developing embryo or fetus. Alcohol, cigarette smoke, illicit drugs like heroin and cocaine, prescription medicines, and certain pathogens are known to have detrimental effects on fetal development. Lipid-soluble substances can readily cross the placental barrier. Therefore, pregnant individuals must avoid exposure to these substances, especially during the first eight weeks of gestation when major organ development is occurring, to prevent conditions such as fetal alcohol spectrum disorders (FASD), which include a range of physical and cognitive impairments. The placenta, while providing essential nutrients and oxygen to the fetus, also allows for the two-way exchange of substances. The pregnant mother's role includes avoiding toxic substances such as alcohol which can inflict lasting harm upon the fetus. Additionally, prescription and over-the-counter medications, along with certain environmental exposures like radiation and components in plastics and pesticides, are also considered teratogens and should be managed with care.