Al-jawab billahi at-taufeeq (the answer with Allah's guidance)
It remains obligatory, unless the woman genuinely fears harm, with near surety, or sickness for herself or for the child. "Genuine fear" is that which is based on: previous experience, clear unmistakable signs, or being informed by a qualified Muslim doctor who is not outwardly corrupt. Then it would be permissible for her not to fast, but to complete them later. However, there is no extra reward for fasting whilst pregnant.