There are two schools of thought on whether or not to worm a pregnant cat. While the general opinion is that it is not recommended, there are certain wormers that are considered safe, and certain situations that may merit the use of a wormer on a pregnant feline.
For decades, it was thought that you should worm a pregnant cat before she is pregnant, twice during pregnancy and two weeks after giving birth. More recent information states it isn't safe to worm a pregnant cat unless absolutely necessary.
The only wormer indicated by the Food and Drug Administration (FDA) as safe to use in pregnant cats is pyrantel pamoate. It is effective in treating roundworms and hookworms, but not tapeworms.
A pregnant cat should be taken for regular vet check-ups. If any unusual behaviour or symptoms develop, a visit to the vet is recommended.
Other Safe Wormers
Piperazine is also indicated as being OK to use, but is not preferred due to problematic side effects.
Natural herbal remedies for worming should not be used on a pregnant animal. These remedies are not regulated by the FDA, and many solutions contain wormwood, which is known to induce abortion.