Greetings. Hyperpigmentation may be due to many reasons - and the cause and the disorder may vary depending on site of the face involved and the color of hyperpigmentation. You have perioral hypermelanosi - this could occur due to vitamin deficienes, or due to past allergies/allergic tendencies, etc. See a qualified deramtologist near you and get evaluated and treated. if you dont want to take treatment during pregnancy, then wait for a few months - till after delivery. Warm regards, Bengaluru.