`Iddah or a woman’s post marital waiting period, is the period in which a woman waits before she may remarry to verify that she is not pregnant, or out of mourning for her deceased husband. (See: Ahmad ibn Naqeeb Al-Misri, The Reliance of the Traveler)
Wisdom of Its Legitimacy:
1- To discern whether the woman is pregnant or not.
2- Shari`ah has ordained the period of `Iddah to avoid any confusion of lineage which may result from the woman’s pressing need of marriage.
3- The period a woman spends in `Iddah whether short or otherwise sheds light on the seriousness of marriage and how far it is a sacred bond.
4- It allows the man and the woman to think twice before breaking up the family tie, especially in cases where divorce is revocable.
Rulings Pertaining to `Iddah:
As for the widowed woman whom her husband dies while leaving her pregnant, her waiting period ends with the delivery of her baby. Allah Almighty says, “…And for those with child, their period shall be till they bring forth their burden…” (At-Talaq: 4)
However, if the widowed woman is not pregnant, her waiting period ends after completing four months and ten days. Allah Almighty says, ” Such of you as die and leave behind them wives, they (the wives) shall wait, keeping themselves apart, four months and ten days…” (Al-Baqarah: 234)
As for a divorced woman, her waiting period ends when three intervals between menstruations have finished, if she is not pregnant. Allah Almighty says: “Women who are divorced shall wait, keeping themselves apart, three (monthly) courses. And it is not lawful for them that they should conceal that which Allah hath created in their wombs if they are believers in Allah and the Last Day. And their husbands would do better to take them back in that case if they desire reconciliation. And they (women) have rights similar to those (of men) over them in kindness, and men are a degree above them. Allah is Mighty, Wise.” (Al-Baqarah: 228)
If the divorced woman – like the widowed one – is pregnant, her waiting period ends with the delivery of her baby.
(`Abdul-Karim Zidan, Nazarat fi ash-Shari`ah al-Islamiyyah)