Which substances are known to cross the placental barrier?

Viruses are known to cross the placental barrier, which can lead to significant health risks for the developing fetus. The placenta serves as a filter, allowing certain substances to pass through while blocking others. However, viruses are capable of penetrating this barrier, affecting fetal development and potentially causing congenital infections. Examples of viruses that can cross the placenta include cytomegalovirus (CMV), rubella virus, and HIV, among others.

While hormones, minerals, and vitamin supplements also play critical roles in pregnancy, they either do not cross the placenta in significant amounts or are regulated in their transfer to ensure fetal safety and appropriate development. Hormones, such as insulin or certain steroid hormones, are usually synthesized by the fetus or the maternal tissues as needed. Minerals are often transferred according to the body's needs but do not pose the same direct infection risk. Vitamin supplements may primarily be absorbed or utilized by the mother, and their passage is often carefully managed.