Heard from a very trusted friend of mine who reared many cats,
including a couple of dogs.
On one of his cat feeding rounds, he stumbled upon this pregnant
female (obviously) cat. My friend immediately took a mental note to
remind himself to include this feline in his daily set dinner
around the blocks.
A few weeks later, the cat was nowhere to be seen.
Another week pass, he heard a soft mew during one of his daily
round and saw the same cat, delivered but weak. My friend places
the food and it ate voraciously.
A week or two later, he found the cat wondering around... searching
for its kittens... which is nowhere to be found. After some time of
searching and findings, he concluded the following:
1. The kittens were placed in a side drain alley
2. Whenever it rains, the mother cat would carry one by one to a
safe place
3. Whenever the mother forage for food, the kittens were left
alone
Thus...
The litter were killed when the rain comes heavily and at least one
was washed away. Secondly, whenever the mum was away, rats would
come and drag off one of the kittens, easy meal.
In the end, all the kittens were gone. 
-------------------------------------
The next time it was pregnant, my friend brought it home and gave
it a warm box(I think). Now it is a happy mother of a wonderful
litter. FINALLY! 
