It would be wrong to say that discharge necessarily signals disease. At a certain period, for example 6-7 weeks of pregnancy, a small amount is normal. But even further, yellow secretions during pregnancy can signal thrush - a fairly common disease in the early stages. You will not confuse thrush with other diseases; a clear sign is the sour smell and curd-like consistency of the discharge.
From 9 to 13 weeks, moderate yellowish discharge without odor, itching or pain is the norm. Pay attention to the consistency; clear, uniform, moderate, odorless yellow discharge is acceptable during pregnancy in the first trimester.