I just thought I would share my story because I had the same questions that I see on this forum frequently when I started pumping. Your mileage may vary! My LO is 16 weeks and is in daycare 5 days a week from 7:15 a.m. to 5:15 p.m. She switches back and forth from breast to bottle easily. Although lately she is distractible and can be a little fussy
I knew before my LO was born (Nov. 2010) that I would have to leave her for an entire day when she was 5 weeks old to attend a work-related conference, even though I was still on maternity leave, and that I would have to go back to work when she was 8 weeks old. So when she was 3 weeks old, I started pumping an ounce and letting DH give it to her in a bottle, and then nursing her, once a day. Fortunately she took the bottle without a problem (although she did look at DH like, hey, what's going on here, LOL).
I had to figure out how much pumped milk to have on hand for the day of my conference, so I checked out the charts in A Nursing Mother's Companion to get a rough idea. I figured out she would need about 10 ounces, if she ate from the bottle at the same "rate" that I nursed her (which she didn't do, and I understand most babies don't). So that gave me 2 weeks to save up 10 ounces of BM, since I started pumping when she was 3 weeks old. But I also decided I had to leave her with 16 ounces, not 10, because I was not going to be the mom who got stuck in traffic or something and not have anything extra at the house to give her. It was so hard in the beginning, because I would pump after nursing and only get 1/2 an ounce or a few dribbles. What really helped was pumping at night, because she would wake up, nurse from one side, then fall back to sleep, and I would pump the other side, getting maybe 3/4 of an ounce to an ounce. I froze what I got. I think at one time I had maybe six or seven containers with a little BM in them in the freezer. I treated it like gold!
Conference day came and I had my 16 ounces of frozen BM. She actually ate about 9 ounces that day. I had to take my pump with me and pumped standing in a restroom stall with the pump hanging off the purse hook, using the battery pack. Fortunately I was able to take breaks when I needed them but I could only pump twice and got about 7 ounces. This is the first time I pumped without nursing her either before or after. So I freaked out and thought there was something wrong with me that I could not get 10 ounces and that I would never be able to go back to work. I thought I had a low storage capacity because my breasts were small. I thought the only reason I produced enough milk for her was because she was nursing every 2 hours.
I continued to pump at night until I went back to work because I was convinced that I could not pump enough during the day for her. And at first, I didn't. I sent her to daycare with 4 3-ounce bottles, of which she would eat 3, and I would freeze the 4th. I had to pump four times a day to barely get 10 or 11 ounces. Then a few weeks in, a few things clicked. First, pumping four times a day was not sustainable. I was getting no work done, and spending all my time going to the (single-user) restroom to pump. Second, my LO was not content with 3 3-ounce bottles (or at least my DCP thought she was not content) and my DCP asked me to put a little more in each bottle. She did not want to give her the 4th bottle because it was too close to the time I picked her up.
So, I just thought, I am going to have to pump only three times a day and make the best of it. It turns out that by pumping for a full 15 minutes 3 times a day I was able to get more milk than pumping for 10 minutes 4 times a day. Another thing I did (which many people cannot do) was to "inform" (not ask) my boss that I would be pumping in my office with the door closed (we have kind of an open door policy) three times a day but that I would be available by email and phone during those times. I put a sticky note on the door and sent my colleagues a one-time email telling them what I was doing so they would take it seriously. I also put a chair in front of the door just in case someone doesn't see the sign. I work while I pump.
So now I pump 3 times a day and get about 14 ounces a day (my production increased a little). I get to work 15 minutes early and pump first thing in the morning (after nursing LO at around 6:30 a.m. and taking her to DC at about 7, my first pump is around 8:15). Then around 11:30, then around 3. I send 3 4-ounce bottles a day, and don't fuss with an "emergency" bottle because it is too stressful to try to produce an extra bottle a day. In reality, my LO has two parents capable of picking her up so it would be a true emergency if neither of us could get there on time. Am considering asking my DCP to store some BM in her freezer in case that ever happens. Don't know why I have not yet done so. I freeze the few extra ounces I get. I nurse LO as soon as I get home, around 6 p.m. I have found drinking a LARGE glass of water in the morning with breakfast and plenty of water and food throughout the day really helps with the pumping-- I usually get almost 5 ounces on the first pump. Five ounces!! From someone who thought she would only ever be able to pump 3.5 ounces at the very most!
So I guess I'm posting this to say if you are nervous about pumping once you go back to work or for building up a freezer stash, try to be little relaxed about it for a few weeks because you will figure out what works for you and your LO. Also, now I leave my pump at work because it is so darn heavy. I take it home on the weekends and at home I also have a manual pump for the (rare) occasions LO sleeps longer than 4 hours at a stretch. Another thing-- it's DH's job to wash the pump parts and the bottles every night-- I'm not doing it. We also have two sets of horns/valves just in case we are super busy.
I hope this helps someone. Wish I had found this forum before I had to start figuring it out myself.