I will be 12 weeks pregnant during a january trip to nicaragua (pacific coast). I am worried about dengue fever and malaria. Should I cancel?

Mosquito borne . Whether or not you cancel your trip depends entirely upon your own risk/benefit assessment. In any tropical environment where there are mosquitoes there is obviously a risk of acquiring a variety of infections. Dengue, in particular, has become increasingly common. This depends on where in nicaragua you will be going. Often there are jungle trips associated with the resorts.