Carla,
Wow! That sounds really rough - so sorry about the pregnancy.
I'm 41 years old and was very conflicted about whether to get a tissue or mechanical valve. Ultimately, I chose mechanical (you can use the "Advanced Search" under my username to see in detail why, but the bottom line is that for me, I preferred the risks and lifestyle associated with anticoagulation therapy to the prospect of a reoperation. On the average, according to at least one study I read, tissue valves don't last quite as long in younger folks than in folks over 65. My research led me to believe that I would likely need another valve replacement in about 12 years if I got a tissue valve. So I went cyborg
But, if I were a woman and having children were important to me, and a tissue valve greatly simplified that, I could see having made a different decision. Everyone on the site will tell you it's a personal decision. My wife said if she were me, she would have gotten a tissue valve (and believe me, she had all the same information I had). For her, that would have been the right decision, in part because she is terrible about remembering to take pills. I'm more type-A, so I wasn't as worried about forgetting to take my coumadin. The good news is that both options (tissue or mechanical) are VERY GOOD! I don't think you can make a wrong choice here - either way, you will be infinitely better off I think. I asked a lot of people who didn't need new valve what they would do if they were me. I got a whole spectrum of responses. Some liked tissue better because "it's more natural and works more similarly to the way the body already works". As far as the prospect of a valve-in-valve (balloon) replacement down the road, the technology definitely seems to be advancing on that front. Right now, it's only used in folks who have a high surgical risk, but someday it may be commonplace. I think most on the site would tell you that there are no guarantees, but that advancements related to both tissue (last longer; possible valve-in-valve in the future) and mechanical valves (lower-risk anticoagulation; valves that don't need as much anticoagulation) are being made at a steady pace. So the future looks bright for both. My surgeon even advised me to get a tissue valve. He believes that the new tissue valves will last even longer than the ones in most people today (search for posts by Norm-of-the-North - he did his homework and picked a great valve - he's also a case study in a journal paper now). Eventually, my surgeon agreed to give me a mechanical valve when he realized I had already successfully self-managed coumadin for another previous issue. But he installs 99% tissue. The nice thing about tissue is that for many people, once it is in, you forget about - and life goes on. A key bit of wisdom I got from this site is that there are no guarantees with either valve. With a tissue valve, you might end up needing coumadin anyway (if you get atrial fibrillation, for example). And with a mechanical valve, you might end up needing a reoperation anyway (due to pannas growth, for example). So with either valve, you are placing a bet. But they are both good bets. And if you still want to have a child, the decision may be determined primarily by that. I think others on the site would be much more knowledgeable than me on that point.
Anyway, sorry for rambling on, but by posting here you have done a wonderful thing for yourself - you've opened yourself up to a very supportive and knowledgeable community. I don't know what I would have done without them. You still have to think for yourself and make your own decisions, but there are smart and caring people who have been through every angle of this stuff that you can imagine, and they want to help you get through this.
Best of luck and welcome,
pem