By Baby Center:
No. When it comes to breastfeeding, there's no debate — bigger isn't better. Breast size is irrelevant.
The size of a woman's breasts is mostly determined by how much fatty tissue they contain. But this tissue doesn't have anything to do with the quantity or quality of her breast milk.
When it's time to produce milk, hormones — triggered by the baby's birth as well as by nursing — stimulate the mammary glands in the breasts to secrete milk and push it into milk ducts under the nipple and areola (the dark area around the nipple). When a baby sucks, the milk flows into her mouth.
A nursing mom's breasts do get larger as they fill with milk — and even during pregnancy, as her mammary glands prepare for the job ahead. But the amount of milk she produces is dictated by her baby.
It's a nifty system: If a baby sucks more, her mom produces more milk. If a baby sucks less, Mom's milk production drops off.