Girls genetically are meant to be over 200lbs. Anything under that and they are anorexic and will produce weak offspring. That's been scientifically proven.
How about that she can't probably walk up a flight of stairs? Physics can apply to health as well.
Where is your proof that a 200lb lady births healthier babies than a >200lb woman.
You aren't even taking height into the equation. To give weight only makes your whole theory bunk.