Hi W. - congrats on being a mom-to-be and for planning to breastfeed! The benefits are soooo numerous that I couldn't even list them all here, but the gigantic benefits include decreasing your cancer risk AND your child's cancer risk (and the longer you breastfeed, the more protection you continue to accrue), a drastic decrease in your child's risk for obesity, and increased protection against illness (thanks to amazing, living immunological factors that your breastmilk provides!) for your child *as long as* you are breastfeeding him/her.
Breastmilk is always healthy, ALL the time. It doesn't suddenly lose it's nutritional value, no matter how young or old the baby is who is nursing -- and that's a medical fact. Some people will try to tell you that when your child reaches a certain age that breastmilk all of a sudden becomes "worthless" after a certain date, but that's a complete lie! Whoever tries to feed you such misinformation is clearly NOT well-educated on breastmilk & breastfeeding!!!
Now onto weaning. If you are really concerned about weaning, here's a fantastic web page with lots of different resources - you can read about weaning techniques, different approaches to weaning, etc:
http://www.kellymom.com/bf/weaning/index.html
OK, so that's one good place to start your research on weaning. However, rather than worrying about weaning your little baby-to-be before you've ever even started breastfeeding, I would like to suggest that you focus on first things first: setting yourself up for a successful start at breastfeeding. :)
Would you be open to refocusing your energy on reading reliable resources like Dr. Jack Newman's "Ultimate Breastfeeding Book of Answers" (by J. Newman, MD and Teresa Pitman) and attending non-profit mother-to-mother support meetings that are supportive of breastfeeding now while you're pregnant and after the baby comes (like LLL http://www.lllusa.org/web/ClevelandOH.html and DFB http://groups.yahoo.com/group/ClevelandDiaperFreeBaby )? Doing things like this will help you breastfeed successfully - you can worry more about the weaning after you've gotten the breastfeeding working!
As far as breastfeeding goes, I think it's really important to take the experience as it comes instead of forming too many expectations about how long you want to do it, when or how you want to wean, etc. I'm only saying this because of my personal experiences with breastfeeding --> I had to work really hard at and fight for being able to breastfeed both of my babies, which I didn't expect. The first 8 weeks for each of my babies was a real challenge in terms of our getting breastfeeding well established, and I'm SO very glad and grateful that I hung in there, reached out for support, and stuck it out through the learning stage of breastfeeding (because even though it might be natural, it is definitely a LEARNED skill and was challenging for us)!
Please give yourself & your baby a good 6-8 weeks to truly give breastfeeding an honest, devoted effort - and I cannot stress enough how important it is to seek out the support and help you might need BEFORE your baby arrives. Unfortunately, most pediatricians and hospitals (nurses, etc.) are not good at providing accurate breastfeeding support or info. It is *so* important to get the name & number of a good lactation consultant who is an IBCLC, AND to get in touch with a breastfeeding support group like La Leche League. These resources are solely focused on breastfeeding information, research, and support - it's their expertise. Having the IBCLC and LLL contact info at your fingertips (and USING THEM if something doesn't seem to be working just right) will help you nurse successfully! Also, double and triple check any info you get about breastfeeding from your doctor or nurse - accurate breastfeeding information exists, but misinformation is sadly still much more common.
More on weaning... If you're interested, I'll share with you how my daughter weaned (if not interested, you don't have to read any further!). Her weaning was not difficult for either of us - in fact, it was so subtle and gradual, I can't even tell you the date she last nursed. Breastfeeding just slowly faded out. She is my 1st child (now 3.5 yrs old), and she weaned at around 2.5 yrs old while I was pregnant with my 2nd child (who is now 10 months old and thankfully still loves to nurse). My 1st had a very gentle weaning, led a little bit by both of us - we each had needs and were able to work together over time, making small adjustments all along the way, so that breastfeeding & weaning was pleasant for both of us. Sometimes I did put limits on nursing, and sometimes she did. Anyway, I plan to go this same route with my 2nd baby. Stopping nursing suddenly is just not at all appealing to me (engorged breasts, no thank you!) nor is it appealing to my babies (too sudden, too confusing, a bit unsettling to say the least).
Breastfeeding/weaning is a process, a dance between mother and child that evolves over time. For us, breastfeeding has been such a fantastic experience, even through the difficult beginnings and any temporary frustrations (teething, for example, can cause a temporary nursing strike or a change in nursing frequency) - overall I just cherish the times between me and my children that were spent cuddling and nursing together.
Best wishes for a gentle, empowering birth and a wonderful breastfeeding relationship with your baby that is surrounded by support and encouragement!