Reference: Fataawa Ramadhaan – Volume 1, Page 374, Fatwa No.333
Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Fatwa No.10727
Question: For three years my wife has been giving birth at the beginning of the month of Ramadhaan and [as such] has not fasted three Ramadhaans. Advice us as to what is the expiation?
Response: It is obligatory upon her to hasten in making up what the outstanding fasts from the fasts of Ramadhaan for the previous three years, just as it is obligatory upon her to feed a poor and needy person for each [missed] day [of Ramadhaan] an amount equivalent to half a saa' of wheat or rice or that which is similar to them from the staple diet of the land. That is due to her delay in making up the fasts [from the previous Ramadhaan] until the arrival of the next Ramadhaan – [only] if she delayed making them up whilst she was able to do so.
And with Allaah lies all the success, and may Allaah send prayers and salutations upon our Prophet Muhammad (sal-Allaahu ‘alayhi wa sallam) and his family and his companions.
 One saa’ is equal to four mudd, and one mudd is equal to the amount held by cupping the two hands together. It is a measure by volume not by weight.