Can I use products with rosemary essential oil in it while pregnant?

Why would you ? By definition, "alternative" is different than modern western medicine. Generally any drug, herb, treatment, or oil that stands up to rigorous scientific scrutiny is included in modern medicine. Many alternative practices, oils etc do not stand up to scientific scrutiny and cannot be shown to work.nor safe. Some could do serious harm. Check https://nccih.nih.gov/ for research.