Which antibody class crosses the placenta to protect the developing fetus?

1. IgG is a major antibody of late primary responses and the main antibody of secondary responses in the blood. 2. It is a monomeric antibody that clears pathogens from the blood and can activate complement proteins. 3. IgG is also the class that crosses the placenta to protect the developing fetus from disease. 4. IgA reaches the newborn through breast milk rather than through the placenta, which is the usual mix-up. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 21 "The Lymphatic and Immune System", section 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies_