This is a very common saying that people make about soon-to-be mothers. But is it really true? Can you tell what the gender of a baby will be based on how the mother's belly is shaped?
From your source:
Like any unscientific gender test, it's accurate about half the time
50% isn't much, you might as well flip a coin.
Also from your source:
Many things factor into the shape and size of the belly during pregnancy, though gender does not make the list as far as medical science is concerned.
So even your source admits that this is not based on scientific fact. I haven't found any papers actually analyzing this "test", which isn't really surprising, but the BBC has an article explaining why it will not work:
Two variables determine the nature of a pregnant woman’s bump. The first is the size of the baby. It is true that on average baby boys weigh more at birth than baby girls, and so this could make the bump for a boy slightly bigger. But this small difference in weight does not change the shape of the bump.
The second is the position of the foetus in the womb. If it has its back alongside the mother’s front this makes her belly stick right out. If the baby’s back is parallel with the mother’s back the result is that the abdomen looks flatter. And as the position the developing baby adopts is not dependent on its sex, it is a myth that the shape indicates whether it is a boy or a girl. source
There is also an article on WebMD about this myth:
"How you carry simply has to do with the tone of your muscles and the position that the baby is in," Beard says. These factors, along with your body shape and how much weight you gain during pregnancy -- not the baby's gender -- will determine how low or high your belly sits. source