The hospital informed you that you hadn’t had chickenpox (varicella) in the past probably because they didn’t find antibodies against the Varicella-herpes-zoster virus in your blood. The immune system creates antibodies against any infective agent during and after overcoming the infection. These antibodies protect you from further infections with the same infective agent. It is very important not to get infected with chickenpox during the first trimester of a pregnancy because the virus can damage the embryo. That’s why you have to avoid contact with people who have chickenpox or shingles (herpes zoster). Herpes zoster is a derivative of chickenpox and it is also contagious.