All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If the pregnant woman fears for her life or for the life of her fetus when she fasts, it is lawful for her to break the fast and make up later the same number of days she had missed to fast during Ramadan. Her ruling is similar to the one of a sick person who can’t fast fearing to harm himself. Allah Says (what means): {So whoever among you is ill or on a journey [during them]-then an equal number of days [are to be made up].} [Quran 1:184] The same ruling applies for breast-feeding women if they fear for themselves when they breast feed their babies while fasting, or if they fear a lack of breast feeding milk. Some Imams believe that they should make up the same number of days later and give an expiation of one Mud (543 grams) of meal for each day.
Allah knows best.