Assalamu alaikum wa rahmatullahi wa barakatuh.
I care for over 20 stray cats and already have 12 kittens. However, due to severe financial hardship, I cannot care for more litters. Two female cats likely conceived after mating a few weeks ago, and if a vet confirms they are in the early stage of pregnancy, would it be Islamically permissible to spay them to prevent further suffering? Or should I wait until after they give birth?
Jazakum Allahu khayran.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Sterilizing cats for an overriding beneficial purpose is permissible. It is stated in Al-Muḥīṭ Al-Burhānī: "It is mentioned in the chapter on Uḍḥiyyah of Al-Nawāzil, concerning the castration of cats, that there is no harm in it if it serves a benefit or wards off harm from it." (End of citation)

Accordingly, it is permissible for you to sterilize these cats, whether before they give birth or after. Likewise, aborting the fetuses of animals is permissible if there is an overriding beneficial purpose for doing so, and this is not comparable to the abortion of a human fetus.

Allah Knows best.