Some commuters don't give up their seat for pregnant women because they fear offending someone who is just overweight

The BBC has this insight:

It's a minefield of mixed signals, indecision, guilt and offence. All played out painfully in public on a crowded bus or train.

Some people are just selfish, yes, but the average commuter would probably give up his or her seat for a pregnant woman, with good grace. It's just not that straightforward.

For a start, he might not have noticed her, and is instead lost in a book or World Cup supplement. Few people repeatedly scan for those more in need of a seat at every stop. And where does his area of responsibility end - shouting distance?

Then there's that nagging doubt - is she pregnant, fat, or just wearing a baggy top?

Whatever the discomfort of offending a pregnant woman by staying seated, is it preferable to the excruciating awkwardness of effectively telling a woman, within earshot of about 20 people, that her tummy is so inflated it looks as if there's a baby inside? . . .

No wonder some passengers are frozen by agonising indecision. A survey by gurgle.com, a website owned by Mothercare, says 84% of pregnant women regularly have to stand - and one of the reasons under discussion on its messageboard was that seated commuters don't want to offend the non-pregnant. To help make things clear, Mothercare sells "Baby on Board" badges. . . .