From Creatures Wikia
A Painful Pregnancy may be experienced by female Creatures who suffer from a genetic mutation that causes their body to release pain whilst they are pregnant. Whilst not immediately life-threatening, painful pregnancies can be extremely uncomfortable for female Creatures, and may distract them from laying their eggs, further increasing their discomfort.
If a female Creature suffers from pain pregnancies, progesterone should be injected shortly after she has become pregnant in order to reduce the amount of suffering she experiences, or the Eggernator can be used to remove the egg from her body. It may be better, however, to prevent her from breeding at all, as chances are the mutation will be passed along to her offspring as this is an inheritable mutation.
Painful pregnancies can occur in all Creatures games, but are relatively rare. There is no cure for this mutation.