State that some pathogens and toxins can pass across the placenta and affect the fetus

Some pathogens and toxins can pass across the placenta and affect the fetus. The placenta, while serving as a protective barrier, is not entirely impermeable; certain harmful substances can still reach the developing fetus.

Pathogens

• Vertical Transmission: Infections such as cytomegalovirus (CMV), HIV, and syphilis can be transmitted from the mother to the fetus through the placenta. This vertical transmission can lead to serious complications, including congenital anomalies, growth restrictions, and other developmental issues in the fetus.
• Mechanisms of Infection: Pathogens may cross the placental barrier by infecting placental cells or through direct contact with maternal blood. For example, some bacteria can invade trophoblast cells, which are part of the placenta, allowing them to reach fetal tissues.

Toxins

• Environmental Toxins: Various environmental toxicants, including heavy metals (like lead and mercury), pesticides, and certain chemicals (like perfluoroalkyl substances), can also cross the placenta. These substances may disrupt fetal development and lead to adverse health outcomes such as low birth weight or developmental delays.
• Impact on Fetal Development: Exposure to these toxins during critical periods of fetal development can result in endocrine disruption, oxidative stress, and epigenetic changes that adversely affect the fetus