I had a friend who had liver damage that was so severe she looked a full 9 months pregnant from the fluid backing up. She was an alcoholic and refused to see a Dr until it was too late to save herself. She wouldn't leave her house the last few months before she died because she knew she'd be asked if she was pregnant every time. She was very skinny otherwise.

There are many reasons not to ask a woman about it. She may have a medical problem and doesn't want to have to explain it. She may have just had a miscarriage or have found out that the baby's life isn't viable. It totally outweighs any benefit of asking without knowing the situation ahead of time.