A woman is born with a finite number of ovum (why? It's just a cell) and burns one each month, every month, until age say 45. Chicken are descended from the asian red jungle fowl, which does that but when the bamboo conditions are right and there's easy access to food everywhere, they go through their monthly cycle every day, laying an egg daily.
The GSC's big win here is that (and this is Headcanon that connects boths of yours) GSC-treated females can gestate multiple hybrids per month. Beginning at 12, which is the average, at triple speed per month they'd run out of ovum at 23, because they used 33 years worth of ovum in 11 years.
That way, a GSCbreeded has finished her duty by age 23 and is free to war about. I guess that what I'm saying is>TFW NO GSC PREGNANT-WITH-MUSCULAR-ARMS WARRIOR WAIFU ;__;