How can a married woman honor her parents when they prevent her from helping them with household chores due to her pregnancy?

Allah knows best what is in your hearts, whether it be mercy towards your parents and tenderness towards them, or something else, or whether your kindness to them is out of hypocrisy. If you are righteous and sincere in your intention of kindness, then Allah forgives unintentional slips for which no harm was intended. Righteousness is not limited to financial or physical service; rather, it includes elevating their ranks in the Hereafter by teaching them the rulings of Islam, enjoining good upon them, forbidding evil from them with the most respectful words, supplicating for them and seeking forgiveness for them, smiling at them, not showing distress in front of them, maintaining constant contact with them, writing to them, praising them, and acknowledging their فضْل (virtue/فضل).