Aromatherapy diffusers can be used in pregnancy to manage symptoms like nausea, anxiety, and insomnia by diffusing essential oils like lemon, peppermint, and lavender. They can also help with headaches, congestion, and relaxation, especially during labor and after childbirth. It's crucial to consult a healthcare provider or certified aromatherapist before use to ensure safety and proper dilution, as improper use can lead to side effects.