|This article is about an older version of DF.|
A pregnant female dwarf will can have a miscarriage under extreme circumstances, including being dehydrated or starving while pregnant. This causes a strong negative thought, the same as losing an existing family member. With many other factors, your dwarf might snap which in most cases will almost always cause some fun.
Keeping women out of the military can help mitigate this (along with babies being carried into battle), as can ensuring that your food and drink stockpiles are kept sufficiently full. Jailed or otherwise incapacitated dwarves may still be at risk, though, due to the seemingly low priority of "Give Food" and "Give Water" jobs.
Due to a bug, the game checks the dwarf's current Hunger instead of her Thirst to determine if she is dehydrated, resulting in a miscarriage if she merely becomes visibly Hungry.