All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
According to the reliable opinion of the Shafie School, it is forbidden to abort a pregnancy in all stages of growth. Although, the degree of prohibition varies according to the different stages of growth, it is sinful to undergo abortion in any of these stages. In case of abortion, the Shafie School obligates offering Kaffarah (Expiation) of murder. Al-Ghazali (May Allah have mercy on him) pointed out: "When man`s sperm enters the womb and mixes with the woman`s ova, this represents the beginning of human life, and the more advanced the pregnancy the greater the wrong." {Ehyaa` Ulum Al-Deen, vol.2/pp.51}.
This is the reliable opinion of the jurists except the Shafies. The evidence is that abortion is a transgressing against a human growing in his mother`s womb. In principle, it is forbidden to transgress against the living, even if life wasn`t breathed into it (Embryo). Having a feeble body or nursing doesn`t justify abortion and it isn`t permissible to hide behind such invalid excuses.
However, if the doctor decided that keeping the baby endangers the mother`s life, then it is permissible to abort it even after 120 days, as decided by the Islamic Fiqh Academies, because the mother`s life is well-established while the baby`s isn`t. And Allah, The Almighty Knows Best.