The Grand Ayatollah Sistani answered some questions regarding abortion. According to Shafaqna the questions and answers are as follows:
Question: Is a mother allowed to abort the feotus, if she does not want it while the soul has not yet entered it and there is no serious danger to the mother’s life?
Answer: he is not allowed to do that, except if the continuation of the pregnancy would harm her health or put her in an unbearable difficulty.
Question: Sometimes the doctors reach the following conclusion: This foetus is afflicted with a very serious disease; it is therefore preferable that it should be aborted because if that child is born, it will be deformed or will die soon after birth. Is it, therefore, permissible for the doctor to abort the foetus? Is it permissible for the mother to agree to the abortion? And who of the two will become liable for indemnity?
Answer: Just the fact that the child will be deformed or that it will not live for a long time after his birth does not ever justify the termination of the pregnancy. Therefore, it is not permissible for the mother to consent to the abortion just as it is not permissible for the doctor to go ahead with the procedure. And whoever performs the abortion will become liable for the payment of indemnity.
Question: What is your ruling on aborting an “unwanted pregnancy” before 4 months into the pregnancy?
Answer: It is not permissible.
Question: My wife seems to be one or two weeks pregnant and we already have four children. We don’t want any more children. Under what circumstances is an abortion allowed?
Answer: Abortion is not allowed after the implantation of the [fertilized] ovum [on the lining of the womb], except if the mother’s life is in danger or the continuation of pregnancy will cause difficulty for her that is not normally bearable and there is no other solution but abortion. In this case, it would be permissible to abort the foetus as long as the soul has not entered into it; after the entering of the soul, it is not permissible at all.
Question: What is the ruling on abortion for a pregnant woman who is infected with AIDS?
Answer: It is not permissible, more so after the soul has entered the feotus. Of course, if continuation of the pregnancy poses a danger to the mother, it is permissible for her to abort it before the entering of the soul in the feotus, but not after it.
Source: Ayatollah Sistani