So, experienced moms... how much bigger will they get? Through pregnancy, through breastfeeding? Will they stay that way?
I'm sure there's a range, but I'm curious! I generally wear a 32FF and have found a 34G is already more comfortable. Which means I've effectively grown 2 cup sizes so far, though, admittedly, that's a drop in the bucket for me. 
What say you?
With DS, I started with an A, went to a C when my milk came in, and then back to a B through breastfeeding (he just weaned at 26 months). But it definitely depends on the person!
IIRC, that's pretty much how it went for my mom... A to C with me, then B after pregnancy/breastfeeding (she only BF'ed us for 6 weeks each), then B to D with my brother, back down to a C after all was said and done*. I obviously don't get my boobs from my mom...
I should ask about shoe size, too. I have heard that some women stay the same, but lots grow a 1/2 size or more per pregnancy... I wonder if that's due to increased actual length, or accommodating increased width? Because wearing a 6.5 Wide, I'd rather my feet got longer than wider!
*Of course, now I know she was wearing the wrong size all that time, because her skinny self was in a 34-36 band (I sell bras)-- so with my help, she now wears a more properly fitting 32DD or so. But the principle is the same.
My boobs actually don't change a WHOLE lot. They grow a bit, but it's hard to tell at this point if it's just weight gain overall or actual boob growth. When nursing they're up and down all over the place but through pregnancy, my rib cage expands but I don't think my boobs grow that much. I go from a 34 band up to a 36-38 but my cup size can stay the same or even go down a bit. I use those band extenders, they're a great alternative (for me!) to buying new bras.
I'm sure you know this, but if your cup size stays the same, then your boobs are actually getting bigger. 
The cup volume on a 34D, for example, is larger than a 32D (the cup volume of a 34D ~ = the cup volume on a 32DD). But it sounds like yours don't get a whole lot bigger, in any event.
Right, I do know that :-) There's just a pretty big variance between brands, is all. So pre-pregnancy I typically wore a 34F, but during I can go to a 36DD (which is nice because they actually sell those in the stores here) in some models. Since I don't like underwires while I'm pregnant, I did go and buy some new bras (and got some donated by friends). The 36Ds are pushing it, but the DDs fit ok still.
Post-pregnancy, nursing, is hard to say at this point because I had such a bad hemorrhage with DD that my milk never "came in". I didn't get engorged at all until I went on domperidone weeks later and then it only happened at 4 am when DD slept for a long stretch, at which point I wasn't wearing a bra. And I had different nursing bras anyway, and they were of the "S-M-L" variety rather than cup sizes.
For me, I always went up a size during pregnancy and they pretty much stayed the same through out breastfeeding. Like, pre-preggo I am normally a 34D, and then go to a 34DD while preggo and also while nursing. As soon as I wean, I go right back to a 34D. I'm pretty predictable!
I should probably correct my last post a little. I was a 34DD pre-preggo this time (for some reason they sort of suddenly became DD's in the past year and I only gained about 10 pounds in that year, so I'm not sure what's going on with them.), and have moved to a 34F. And in saying that... it's not any fun. My boobs are soooo heavy! Of course DP just loves it, and says the booby gods are blessing him (or me!)! Ha! He doesn't have to carry these cannon balls around! I think if he had to he wouldn't think they were so grand... or he would never leave the house because he wouldn't be able to stop touching them! LOL!!
Gotcha, spughy!
babytoes, LOL... Unfortunately for both of us-- and my boobs, which will probably venture into UK GG or H territory (US K cups!)-- DH is not even a boob man. He likes them fine, but he's more of a butt and hip and leg guy... luckily I have plenty of those, too. 
My feet never grew with DS. And I hope that it is the same this time (I like my small feet)
I'm sure you know this, but if your cup size stays the same, then your boobs are actually getting bigger. The cup volume on a 34D, for example, is larger than a 32D (the cup volume of a 34D ~ = the cup volume on a 32DD). But it sounds like yours don't get a whole lot bigger, in any event.
I actually didn't know that..I always though cup size was the difference between the circumference of your chest right below you breasts, and the circumferance at your breast (the biggest part). If you have 1 inch difference, than you're a A cup, 2 inches, B cup, etc.... Am I getting it wrong? I'm confused!
Anyway, I went from a 34B to a 36C during late pregnancy and when I was exclusively b-fing DD. They went back down pretty quickly after about 12 months, when I was really feeding only 3-4 times a day.
This time around though, at 15 weeks, my 34 B bra is beginning to feel really snug. I should probably go shopping, but I don't really feel like it!!!!
I went from an A to a B in pregnancy, then to a C when my milk came in. Slowly over time while I was nursing one went back to a B and one went back to an A. :( I've been really hoping that somehow this pregnancy will make them go back to being the same size, but no luck so far.
I didn't know this until I was 30 years old-- I don't think most people do.
But guess what? Both things are true! The 1-inch, 2-inch, etc., difference rule is basically true, and cup size also varies based on band size. How can this be the case? Well, I wish my old fashion blog were still accessible (virus), because I had two huge posts on this. First, if you want to confirm that an A cup is not just a standard "A" volume pasted on to a smaller or larger band, all you have to do is look at a 32A and a 40A the next time you're bra shopping. Not just the band size, but the actual cup is MUCH larger (wish I had my comparison photos handy!)
So how does the 1" difference thing still make sense? I spent a while breaking it down on my blog so that it didn't seem so complicated (I used a cake and frosting example, LOL), but the short answer is-- geometry. We're not 1- or 2-dimensional, we're 3-dimensional. So an additional 1" in circumference/perimeter (1" longer perimeter around the bust than the underbust) translates into a larger volume (3 dimensions) when your underbust is larger. For a more extreme example-- imagine you have a golf ball and you wrap a tape measure around it. Then you add an extra 1" to the measured circumference. Imagine how many cotton balls would fill the gap you've created, between the golf ball and the tape measure. 1 or 2, maybe? Then take a beach ball and wrap a tape measure around IT and add an extra 1" to the measured circumference. Now imagine how many cotton balls you'd have to add to that gap to fill it-- more than 1 or 2, I can guarantee that! You could imagine extending a tape measure an extra 1" around the entire world, another sphere, and you would create a much bigger gap... YKWIM? I know it's hard to picture, but it really does pan out.
Now for an irresistible math interlude...
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Going with my original cake example, if you had a Cake X that measured 8" on all sides (a weird, cube-like cake!), then the perimeter (as if you wrapped a tape measure around it one way) would be 32" (8+8+8+8). Now you frost the cake so that the sides are now 10" high, you have a perimeter of 36" (8+10+8+10). The difference in perimeters is 4".
Take another unfrosted Cake Y that is 9" on all sides, and the perimeter is 36" (9+9+9+9). Then add a layer of frosting so that it's 11" high on the sides, and the new perimeter is 40". The difference here in perimeters (unfrosted vs. frosted) is also 4".
Okay, so far, so good. Cake X is sorta like a 32D, and Cake Y is like a 36D, right?
But what's the difference in frosting volume?
For Cake X, we take the original volume of the unfrosted cake (8*8*8) and subtract it from the volume of the frosted cake (9*8*8-- because only the height of the cake changes-- the width and depth stay the same). That's 576-512, or 64 cubic inches of frosting, LOL.
For Cake Y, it's frosted (11*9*9) - unfrosted (9*9*9) = 891- 729 = 162 cubic inches of frosting.
That's a big difference in frosting. 
Of course, we're not cubes, so this is not an exactly accurate representation, but you get the idea. It really is confusing, and stymied me for a while, too, but it makes sense when you do the math.
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I do think that's one reason (knowing the 1" rule) people think that cup volume is a static thing. Well, that and the fact that American bra manufacturers in particular are terrible about making many sizes outside of 32-38 A-D (maybe DD)-- cheapskates! That encourages you to identify with a cup size-- KWIM? Like we all "know" that an A cup is small, a B-C is/looks average, a D is big, DD is huge and anything bigger is ginormous... But actually, since cup volume is based in part on band, a 30D or 32D doesn't look super big (I mean, not "flat," because it's on a petite person, but not "like a D cup" either). In fact, a 32D is approximately equivalent in actual volume to a 34C, a 36B or a 38A. Not so big. But it's hard to tell a woman who would be more comfortable in a 32D that she wears a D cup if she thinks of herself as a "B" cup type of gal. And it can induce tears to tell a woman she'd be much perkier and more comfortable in a G-cup! Ask me how I know!
But what happens is, if you don't know this (as I didn't!)... when a 34DD is too small in the cup, you move up to a 36DD because you "know" you "are" a DD cup and Victoria's Secret or whatever doesn't carry a DDD/E. Then, because a 36DD has a greater actual cup volume, it "fits"... But not really, because the band is too loose to provide great support. But you just keep on wearing a 36DD, because there "isn't" a 34DDD or whatever and you can't imagine "being" such a "huge" cup size. I wore a 38D for the longest time before a friend clued me in-- now I typically wear a 32FF (UK Size-- like a US 32DDDDD if it existed) when not pregnant, and I look much thinner and am waaaaay more comfortable.
I'll never forget, after having this same conversation with an older friend of mine (~65 years old), she bought new bras and was thrilled. Then we happened to be chatting with another 60+ year old friend of hers and my friend was extolling the virtues of her new bra size and sort of dropped a hint to her friend, like, oh, you probably wear a DD+, too. And her friend, was like, "No, you'd think so, but I'm a C!" Dude... This woman's boobs (in a bra) were in her lap. I'm sure she was wearing like a 40C and could have been wearing a 34DDD or more and been much happier. (Not that there's anything wrong with your boobs being in your lap, BTW, if you don't care or that's the look you're going for. But she might as well have not been wearing a bra at all.)
/end thesis
BUKO!!!! YOU are hilar! :D
Babytoes! Soo funny about your DP! My DH is not a boob man, but ended up with plenty! lol.
Now, to answer your question: I was a 36 D before I got pregnant with child#1. During pregnancy, I went up to a 36 DD. When Nursing, I expanded to a 36 DDD. The lady in the store thought I was crazy when I told her that that was the size i needed. ("There is no way you are a DDD!" she said. "Well, that's what I'd like to try on," I replied. She said, "you look more like a C cup." "I don't care what I look like," I said with some attitude as I had a 6 week old infant who would be up any minute waiting with my husband. "I am wearing a 36 D and am overflowing. I need to know if you carry 36DDD." I tried on that bra, it fit, I bought it and I left.) I was a 36 DDD when I got pregnant with child#2. By the time she was 6 weeks old, it was time to go bra shopping again and I was a 36 I. Yeah... I was shocked, too. There was a time where that size was a bit snug, but that was the largest bra I could find in a store and I have issues with buying something I will prob have to end up returning online. It fits fine now. I am afraid of what I will become when this one comes out and is nursing... lol. I went up 2 sizes with the first, and 4? I think with the second. So I am currently 6 sizes (or more?) sizes larger than my original prepregnancy size. Now... FOR SURE I will have to buy bras online when this one is on the outside. Not looking forward to that. I plan on having LOTS of kiddos, though and I am super curious about what I will be when alll is said and done. I thought I was too big at a D before #1 came into the picture. Now, there is no word to describe what I think of my boobs now that they are an I! Annoying, HUGE, a pain in the behind all come to mind!
I'm not an "experienced mom," as this is my first pregnancy, but I have to say, I started at a 34B (and had been fitted many times and was wearing the right size), and am already a solid 34D on my way to a 34E (or whatever you call the next size up), and I'm only 14.5 weeks. 
Oh my gosh, I was away at work for the weekend, and look at the hilarious thread that I was missing out on!!!
Buko-- WOW, what great info!!! I wish your blog was still up, too, I would definitely read it. :)
I went from 34A pre pregnancy to 36C while nursing the first few months to 36B after weaning.
My feet have grown a half inch in length since my first pregnancy. (your arches fall a bit from the relaxin hormone).
I was a 34C prior to pregnancy, now comfortably back in 36D from last pregnancy. During the first 6 months of breastfeeding they got bigger, likely a DD, but I wore mostly stretchy nursing bras that handled the fluctuation between post-nursing and 'oh my god child, you need to eat now!'. They stayed at 34D for a while, and then when I finished bfing at 2 years, they quickly shrunk back to 34C.
DP is a boob man, I think it's his favourite part of the pregnancy.
Buko, I am stealing your cake example when I teach volume-surface area ratio in cell biology!!! The kids don't really get it, they just smile and nod at me! (I am not, however, getting into the bra cup comparison with them, though basically it's the same situation!!!)
Regardless of what is happening to my cup size, my boobs are sore and heaaaavy!!!!
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