Verbatim · Ayatollah A. Sistani
Fasting is not obligatory on a woman in an advanced stage of pregnancy, for whom fasting is harmful or for the child she carries. For every day, however, she should give one mudd (750 grams) of food to poor. In both the cases, she has to give qadha for the fasts which are left out. Also, if a woman who is not in an advanced stage of pregnancy but fasting is harmful or unbearably difficult, fasting is not wajib on her. She must keep the qadha later and there is no kaffara on her. In both case, if a woman fails to observe the Qadha of the missed fast until next Ramadhan, she must, as an obligatory precaution, give another kaffara because of delaying the Qadha.
Ayatollah A. Sistani sistani.org Q&A #25357 other marjas may differ
Use the fidya calculator to compute the staple-food equivalent for your situation.
For Makarem and A. Khamenei muqallids: the rule is structurally similar but with refinements. Makarem distinguishes harm-to-fetus (fidyah owed) vs. harm-to-self (no fidyah owed); A. Khamenei adds a separate “kaffāra of delay” if the qada itself is then delayed past the next Ramadan without excuse. Tuhr’s app handles each marja’s variant.