Permissibility for the pregnant woman to not fast please see below
For the Shafi position regarding permissibility for the pregnant woman to not fast please see below :
It is permissible for a pregnant woman who does not fast or breaks her fast solely out of concern for the welfare of her child and likewise a nursing mother who does not fast or breaks her fast solely out of concern for the welfare of her nursing child, such as she fears her milk will decrease if she fasts. However, she must make up the missed day and pay the expiation (fidyah).
However, if she doesn’t fast or breaks her fast out of fear for the sake of her child as well as her own health, then the missed fast has to made up but there is no expiation.
The expiation (Fidya) is calculated as one mudd of the main staple food (a dry measure amounting to approximately 0.51 litres) of the place the person is in at the point making up the fast becomes possible for for each day missed.
In today’s time, for practicality, one can adopt the opinion in the school to pay the value of the fidya anywhere abroad (including online payments with the intention it is fidya for one’s missed fasts).
The mudd(s) must be distributed to the poor and the needy. It is permissible to give many mudds to one person, but not one mudd between two or more people. Nor can one give one and a bit to one person, and the same to others.
Information taken from:
In addition, if a reliable medical professional says the child’s life is in danger, it is obligatory for her to break her fast.