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

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.