Dear Kamila Husain,
No Mullahs or "Awliyas" have the authority to throw their opinions and invent laws as "Shari'ah". Such are the Criminals of Islam.
Please remember all your life that whenever someone says "Shari'ah says this", "Islam says that", he or she is trying to fool others by presenting his/her own opinion.
The true guidance must come with a reference from the Book of Allah.
The pregnant woman will fall in the category of the sick.
Reflection on the Qur'an makes it obvious that SAUM is ordained for adults only. If a pregnant woman fasts, her little intrauterine fetus will be suffering from dehydration and starvation and even a vulnerable little life may be put at risk.
"Feeding people": What will the pregnant woman do if she is poor?