Is it obligatory to observe ‘iddah for a woman who has had her uterus removed (hysterectomy)?
Question

                Is it mandatory for a woman to observe Iddha period who actually doesnt have a womb ( operated and taken away due to some health problems)? If so , why?.
Praise be to Allah.
    What is required by this 
    woman if her husband dies is to observe an ‘iddah of four months and ten 
    days, because she comes under the general meaning of the verse in which 
    Allah says (interpretation of the meaning):

    “And those of you who die 
    and leave wives behind them, they (the wives) shall wait (as regards their 
    marriage) for four months and ten days”

    [al-Baqarah 2:234].

    In the event of divorce, she 
    must observe an ‘iddah of three months, because she does not menstruate. 
    That is because of the general meaning of the verse in which Allah says 
    (interpretation of the meaning):

    “And those of your women 
    as have passed the age of monthly courses, for them the Iddah (prescribed 
    period), if you have doubts (about their periods), is three months, and for 
    those who have no courses ((i.e. they are still immature) their Iddah 
    (prescribed period) is three months likewise, except in case of death)”

    [at-Talaaq 65:4]. 

    Shaykh Ibn ‘Uthaymeen (may 
    Allah have mercy on him) said: If she has ceased menstruating for some 
    reason and she knows that her menses will not resume, such as if her uterus 
    has been removed, she comes under the same heading as one who has passed the 
    age of monthly courses (i.e., post-menopause), so she should observe an 
    ‘iddah of three months.

    End quote from Fataawa 
    Islamiyyah, 3/311 

    Although removal of the 
    uterus means that we may be certain that she is not pregnant, it does not 
    mean that observing the ‘iddah is not obligatory in her case, because the 
    wisdom behind the ‘iddah is not limited to ascertaining that there is no 
    pregnancy. 

    Ibn al-Qayyim (may Allah have 
    mercy on him) said in I‘laam al-Muwaqqa‘een (2/51): The purpose of 
    the ‘iddah is not only to ascertain that there is no pregnancy; rather that 
    is only one of its aims and wisdoms. End quote. 

    He also mentioned some of 
    these wisdoms in the same book (2/50, 51) where he said: There are a number 
    of reasons behind the prescription of the ‘iddah, one of which is to 
    ascertain that there is no pregnancy, so that the water (semen) of two or 
    more men will not be present in one womb, lest lineages become mixed, 
    leading to negative consequences that are prohibited by sharee‘ah and 
    wisdom. One of these aims is to highlight the importance of this contract 
    (marriage contract) and show how great and honourable it is. Another is to 
    give a lengthy period of time in which a man who has divorced his wife may 
    take her back, because he may regret it and decide to take her back, so he 
    will have enough time to so. Another purpose is to fulfil the rights of the 
    husband (in the event of his death) and highlight the impact of his loss in 
    the prohibition on adorning herself. Hence the prescribed period of mourning 
    for the husband is longer than that for a parent to a child. Another purpose 
    is to protect the rights of the husband and the interests of the wife, the 
    rights of the child and the rights of Allah that He has enjoined. There are 
    four rights that are acknowledged in the ‘iddah. End quote. 

    And Allah knows best.