There should be some reason, such as life of mother, or child has risk of birth defect, or some other reason. However even without such reason abortion before 16 weeks is not a crime.
There is broad acceptance in the major Islamic schools of law on the permissibility of abortion in the first four months of pregnancy. Most of the schools that permit abortion insist that there must be a serious reason for it such as a threat to the mother's life or the probability of giving birth to a deformed or defective child. However, as the Egyptian booklet."(The Arab Republic of Egypt published a booklet called "Islam's Attitude Towards Family Planning.") says: "Jurists of the Shiite Zaidiva believe in the total permissibility of abortion before life is breathed into the fetus, no matter whether there is a justifiable excuse or not." That would be a pure form of what some call "abortion on demand."
The majority of orthodox Muslims (following the Hanafi school) in later centuries, allowed abortion until the end of the four months. According to them, a pregnant woman could have an abortion without her husband's permission, but she should have reasonable grounds for this act. Most of the Maliki jurists (legal scholars) described abortion as completely forbidden. In their view, when the semen settles in the womb, it is expected to develop into a living baby and it should not be disturbed by anyone. According to Ibn Jawziyyah, when the womb has retained the semen, it is not permitted for the husband and wife, or one of them or the master of the slave-wife, to induce an abortion. After ensoulment, however, abortion is prohibited absolutely and is akin to murder.
The Hanafi school (prevalent in Turkey, the Middle East and Central Asia) allows abortions to take place principally until day 120; some jurists restrict this provision to “good cause”, e.g. if the mother is still nursing an infant and fears that her milk may run out during the new pregnancy. In aborting up to day 120, the woman commits a mere moral transgression, not a crime. The Shafi school (dominant in Southeast Asia, southern Arabia, parts of East Africa) allows abortions to be performed up to day 120. For the Maliki school (prevalent in North and Black Africa) an abortion is permissible with the consent of both parents up to day 40; it is no longer allowed after that. For the Hanbali school (predominant in Saudi Arabia and United Arabic Emirates) abortions are principally prohibited from day 40 onward.
http://www.islamawareness.net/FamilyPlanning/Abortion/abortion3.html