What can cause 3-week-old kittens to suddenly start dying off one by one?

I had a litter do exactly this...and I didn't find it out until too late that the babies were starved because their moma's milk had dried up.

In that case...we had lost a few, and then for some reason I checked her teats by squeazing them gently and no milk came out...but by the time it was discovered, it was too late, the "surviving" kittens were already too weak and too starved to accept our intervention.

They will still nurse a 'dry well' so to speak...it's their instinct...so start giving kitty formula to the ones living every 2 hours, and get them all to the vet ASAP tomorrow morning!

If mom is up to date on shots, then a likely cause is incompatable blood types between mom and kitten. Pedigree cats have found that some blood types are not compatable (never mate a A blood type to a B blood type).

The kittens can start dying within a few weeks. I would take everyone to the vet to see if there is something else involved. You cannot do anything if its caused by the blood types.

Please get her spayed ASAP.

Clarice might be onto something with her answer! It sounds like you are concerned? Reality check(not being a ********),sometimes these situations are beyond our control. You never did say how many kittens were born! Unfortunately the more in the litter, means the strong will prevail,and I am sorry to say that you are there to see the other half. Point being when the weak ones fight for the tit of mom, the weak ones get caught in the struggle and what Clarice said is one possibility! Hope this Q. is on the level? Had 2 bst friends (my felines) for almost 20yrs. All my best to your situation.

I am at the moment hand rearing a kitten, but when i spoke to the vet they adviced me of a condition called fading kitten sydrome..its when they are doing really well but then suddenly start to fade and die for no reason at all. Its like SIDS in children...If this is the cause its nothing you or mummy cat as done wrong its just nature..Look up fading kitten sydrome on your internet and see if they are having any of the symptoms...Good luck

There are too many things it could be for us to provide you with an answer - distemper, FeLV, other viruses, something wrong with the mom's milk, genetics - any one of those things and more will cause litters of kittens to die. You need to get mom and the remaining kittens to the vet, to see if they can determine what's wrong. It's very often a genetic thing, something that mom has passed on to the kittens. Get mom spayed, to avoid more heartbreak.

Take them to the vet. They could have fleas. thats what killed my cats last set of kittens.

How many died?

I've seen a mother cat accidentally kill her kitten by laying on top of it, suffocating it.

Please have her spayed.

Please take them to the vet right away! You can't save them by yourself if you cant find a reason why they're dying

Are you sure she actually has milk?