My wife is pregnant and the doctor advised her not to fast. What must she do, make kaffara (expiation) or pay fidyah (compensation)? In either case, what is the sum and when is it due?

 

If a Muslim physician determines that the inquirer's wife is unable to fast, there is then no objection to her refraining from fasting. She must make up her missed fasts after her excuse ends by fasting a day for each unperformed fast day.

If she is unable to fast even after her excuse ends, then she must feed one poor person two meals for each unperformed fast day based on the average standard of the food she feeds her family.
And God Almighty knows best.