The immunoglobulin which passes the placental barrier in humans is:

There are five known classes of amino globulins: IgG, IgA, IgM IgD and IgE. IgG is the major middle globulin that is found in human serum and the one that has been shown to pass the placental barrier in humans. IgM possesses higher agglutinating and complement-fixing capacity than IgG. IgM has a molecular weight of 900,000. Carbohydrates constitute 7 to 11 percent of the total weight of IgM. IgD constitutes a minor poion of serum immunoglobulins (1 percent). It contains higher amounts of carbohydrate (13 percent) than the other immunoglobulins, but it has an impoant B-cell receptor. No other biological functions have been described for IgD. IgE is the immunoglobulin that has been associated with anaphylactic hypersensitivity. IgE has a molecular weight of 190,000 to 200,000, contains 11 to 12 percent carbohydrate and constitutes .002 percent of the total serum immunoglobulin. IgA is the major immunoglobulin of extracellular secretions. It has a molecular weight of 160,000 to 440,000, had modest agglutinating capacity and its carbohydrate content is two to three times higher (7.5%) than that of IgG. Ref: Levinson W. (2012). Chapter 59. Antibodies. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.