When I was 130lbs my bra size was 34B. Now I am 220lbs and I wear 40D. Will my breast size reduce with weight loss?

A large
amount of weight gain or weight loss as you’ve described will affect the size
of your breasts.  Breast size can
fluctuate with hormonal changes, weight gain or weight loss.  Should you lose weight your breasts will
become smaller but may not be as small or have the shape they once had.  I would suggest reaching your goal weight before
deciding on any surgical procedure.  You
may need a reduction or even a breast lift depending on the amount of weight
you lose.  Be sure to consult with a
Board Certified surgeon to discuss your surgical options in detail.

It is likely that your breasts would become smaller if you lost weight as they were smaller when you did not weight as much.

Your breast size will get smaller if you lose the amount of weight you are describing. I would wait on any breast surgery until you have lost the weight and are stable at your new weight. You may need just skin removed or some breast tissue. Only time will tell.

You will certainly have reduction in the size of your breasts if you lose the 90 pounds to get back to 130.  However, your breasts will probably not be what they were before your weight gain.  The shape will have suffered from the stretching, and you will likely need a mastopexy.

Every woman's breast is a mixture of glandular tissue and fat all intermixed.  The ratio of gland to fat is diiferent in different people and also varies throughout life.  Breasts have a higher proportion of fat with aging.  Breast size changes as your weight goes up and down.  If your breast is composed of a higher percentage of fat , your breast size will change more with fluctuations in weight.  Very dense, glandular breasts may show less change with the ups and downs of body weight.