Final answer:
Microbes capable of infecting the fetus by crossing the placenta are referred to as vertical transmission pathogens, including the TORCH group and Listeria monocytogenes. The placenta regulates the exchange between maternal and fetal environments but is permeable to some pathogens and substances such as alcohol, which can harm fetal development.
Step-by-step explanation:
Microbes that have the capacity to cross the placental barrier and possibly infect the fetus during pregnancy are known as vertical transmission pathogens. Some well-known examples of these pathogens are those that make up the TORCH group, which includes Toxoplasma gondii, rubella virus, cytomegalovirus (CMV), and herpes simplex virus (HSV). Other significant pathogens include the gram-positive bacterium Listeria monocytogenes, which can cause severe illness such as listeriosis, leading to spontaneous abortion or severe fetal impairment.
The placenta serves as a critical interface between the mother's and the fetus's environments, allowing the exchange of nutrients and oxygen while normally preventing most microbes from passing through. However, certain pathogens are able to penetrate this barrier due to their ability to move through layers of cells or capitalize on the natural exchanges that occur between maternal and fetal blood through structures like the chorionic villi. Pregnant individuals are advised to avoid fetotoxic substances, which can include alcohol, nicotine, some medications, and certain pathogens that can be harmful to fetal development, leading to a range of abnormalities such as fetal alcohol spectrum disorders (FASD).