Please treat this as a starting point and check with your OB or dermatologist, since guidance is individual. The widely-followed caution is around retinoids (topical tretinoin/retinol and oral isotretinoin) — many people are advised to avoid topical retinoids during pregnancy out of caution, and oral isotretinoin is strictly contraindicated.
Ingredients commonly considered acceptable by many clinicians include niacinamide, azelaic acid, glycerin/hyaluronic acid, and vitamin C, and mineral (zinc/titanium) sunscreens are a popular choice. High-strength salicylic acid (especially oral) is often flagged for caution, while low-concentration topical BHA is usually viewed more leniently. The reason we won't be more definitive than this is that the evidence is genuinely mixed and the stakes are high — so the right move is a quick conversation with your provider, using this as the list of things to ask about.