That is just ridiculous, it just defies common sense!
My MIL swears by this myth but I feel it is ridiculous. She totally beleives and says that a baby can be born at 7 months but can not be born and survive at 8 months. I don't understand why and how did this even get started?
The longer the baby stays in the womb, the better, yes.
Can a 7-month-old baby survive? Yes! But their chances of having fewer problems (with their heart and respiration and brain development, eye development, etc.) are greater the longer they stay. There's a reason pregnancy is 40 weeks. Lung development is one of the LAST things to take place, usually in those last couple of weeks.
I'd have to say this is a ridiculous myth. Ever visit a NICU?? Come see the difference between a 28wker and a 32wker and u tell me which is better.