Herpes simplex type 2 IgM positive and IgG negative affects pregnancy. IgM is immunoglobulin M and IgG is immunoglobulin G. If IgM positivity is detected when a herpes simplex serologic test is done, it indicates a recent herpes simplex virus infection, and pregnancy during this time may interfere with the normal development of the embryo. IgM is the earliest antibody that appears in the initial humoral immune response. Herpes simplex type 2 serology is positive for IgM, which suggests a recent herpes simplex virus infection and requires prompt antiviral treatment. IgG is the primary antibody produced after the immune response is renewed, which suggests a previous herpes simplex virus infection, and IgG is negative, which suggests that there is no previous infection. If a woman during her pregnancy is found to have herpes simplex type 2 IgM positive and IgG negative, she should go to a regular hospital in time, under the guidance of the doctor for reasonable treatment and reasonable preparation for pregnancy.