Hot temperature can affect the cells of your developing baby. High temperature in the first trimester – above 101.5 °F (38.5 °C) in pregnancy, over several days – may lead to a 3-fold increase in neural tube defects as well as a risk of neurological and structural malformations in the baby.
High temperature in the second and third trimester may cause neurological issues as well. Avoid hot tubs, saunas and steam rooms, and treat high fever by staying well hydrated, and consider taking occasional Tylenol if your temperature goes above these numbers. Occasional Tylenol use is felt to be safe by the great majority of medical providers.