Ok, now that I've got your attention, let me explain. :-P
It is a known fact that motherhood changes a woman's body. This includes her hips, her abdomen, and her breasts.
It is a myth that breastfeeding causes deflated, saggy boobs.
Pregnancy causes the changes in your breasts.
But, I know some women worry that breastfeeding will cause their breasts to sag and be deflated. And I know lots of women that breastfeed their first baby, even if only or a short time, and then wonder, "Breasts: What Just Happened Here?" This is because after weaning they suddenly feel like their boobs are a half-inflated balloon. But, I repeat, it is NOT breastfeeding that causes these changes. It is pregnancy and it is based on a wide array of factors.
Studies have shown that the following factors are most indicative as to whether a woman's breast will sag postpartum:
1) Age---So your breasts are more likely to sag if you are older. Go figure. So will the skin under your neck, on the backs of your arms, and your stomach. And breastfeeding doesn't have anything to do with those areas.
2) Higher BMI---Ok, I am NOT a fan of BMI, but I don't want to get into that right now. What I will say is that people with higher BMIs typically have more skin/fat that is capable of sagging. I myself currently have a BMI of 31, which is considered just over the edge into the obese range. And I certainly have some extra skin/fat hanging around. So it is only natural that I would experience more sag with a higher BMI than a person that is a size 2 with minimal body fat.
3) Higher Number of Pregnancies--- This one is a no-brainer. A woman with one pregnancy will have a lesser degree of sag than the person that had 10 kids. Here is a fun example. My grandma had 10 children. She breastfed the younger children, then used formula for the older children. I hate to say it, but she has a LOT of sag. My mother had 3 children and did not breastfeed any of them. She has more sag than my aunt that had 2 children and did breastfeed. And my aunt that had no children has never had a sagging issue.
So, to summarize:
0 children = minimal sag
2 breastfed children= some sag
3 formula fed children= more sag
10 children = why are my boobs by my belly button? (Sorry grandma, haha).
4) Larger Pre-pregnancy Breasts--- This is another no-brainer. Larger pre-pregnancy breasts means that you have more room for them to sag. If they were tiny, there would not be as much for gravity to affect and not as much skin to allow them to sag. To me, this is also related to "Higher Number of Pregnancies." I went up a cup size at least with each pregnancy. So I was more likely to sag postpartum when I was a size C coming in to my 3rd pregnancy than I was when I was a size A going in to my 1st pregnancy. Like I said, no-brainer.
I'm sure you can find other factors, but these seem to be the ones I hear most often. And genetics. I mean, if your mom's boobs sagged, her mom's boobs sagged, etc and etc....then you will probably sag to a similar degree.
You see, it is the biological chain of events that happen during pregnancy and immediately after delivery to prepare your body for breastfeeding that cause the changes in your breast. Whether YOU plan on breastfeeding or not, your BODY will still prepare for it. That means you will produce colostrum and your milk will come in, whether you choose to breastfeed or use formula. It is these biological changes that cause the changes in your breast, not breastfeeding.
So, after your baby is born, you will realize that your breasts have changed slightly. But if you breastfeed, they will feel more full and firm while you are breastfeeding. After weaning, you will REALLY notice the changes caused by pregnancy. Think about it. Even if you only nurse for a few months, that is a few extra months of having your breasts filled with milk, feeling heavier, full, and firm. And we all know how cleavage is enhanced when your milk comes in.
After weaning, your milk will dry up. They will no longer feel heavy, full, or firm because of the milk. But YOU will still be used to how they felt while breastfeeding. So the absence of milk will make them feel more saggy and deflated. In truth, they would feel that way if you had decided to not breastfeed. The only difference is that they would have had that saggy, deflated feeling in the weeks after delivery.
And remember that it takes around 6 months after birth or weaning for breasts to adjust and start to feel "normal" to you. I'm still nursing and Monkey is 12 months old. If we suddenly weaned right now, I would not expect my boobs to feel normal again until he is around 18 months.
So there you go. If you choose to breastfeed, don't sit there after you wean, look at your breasts, and try to figure out what just happened. Instead, sit there, look at your breasts, and think, "Hmmm. I've been wondering when this would take effect."