Final answer:
IgG is the only antibody class able to cross the placenta, providing crucial passive immunity to the fetus. It is the predominant antibody in serum and is critical for the immune response, including in Rh-factor incompatibility situations where it can cause HDN if an Rh-negative mother carries an Rh-positive fetus.
Therefore the correct answer is option is B) IgG
Step-by-step explanation:
The antibody that is capable of crossing the placenta from a pregnant woman to her developing fetus is IgG. IgG is the most abundant antibody in human blood and plays a crucial role in the body's defense against pathogens. Importantly, IgG is also the only class of antibody that has the ability to cross the placental barrier, providing passive immunity to the developing fetus. This transfer of immunity is essential for protecting the infant for up to six months after birth.
In the context of Rh factor incompatibility, the placental transfer of anti-Rh factor IgG antibodies from an Rh-negative mother to an Rh-positive fetus can lead to hemolytic disease of the newborn (HDN), a serious condition. This underscores the functional significance of the ability of IgG to cross the placental barrier.