You ate so much, you feel as if you're pregnant. Also, your stomach sticks out massively.

"allow it" means to just leave something alone, or don't worry about it. People in West London say this quite often.

when you eat so much, that your stomach looks pregnant

After a very large meal, when your stomach bulges a little with food, and you can kinda pretend you're pregnant, but the baby inside is only actually food.

When a person, typically a thin one, indulges in a large amount of food which makes their stomach stick out from the fullness as if they're pregnant.

after you eat, the fattyness in the lower abdominal area. can be mistaken for 3-4 monthes pregnant

A kind of belly that you get after eating a ton of food, where to the point where your belly is like a woman's child in the womb, where the term gets it's name. This fortunately is temporary, considering you shit all of the food away in the end of the process.