That depends on the type and size of hernia you're describing.  Most hernias represent a compromising of the strength of the abdominal wall.  With an impending pregnancy and the accompanying enlargement of the uterus, that weakness could become a problem.  The weight of a pregnant uterus could push other abdominal organs into the weakened pouch of skin or the uterus itself.  If there are any risks that are imminent, you mainly need to watch your cat closely for any sign that the hernia has grown suddenly.  If it has, your veterinarian should determine if attention is warranted.

Helpful buckeye