Beta doubling?

[jennl]

Hello ladies, (also posted on November board)
I had beta #4 on Saturday and will be going in for #5 before work in the morning. This is through my obgyn -- my RE thought my numbers were fine and didn't want to repeat any more blood work. I'm scheduled for an u/s with him on Sunday morning. However, with 2 m/c my obgyn went ahead and ordered blood work up until I see her this Wednesday. So far I've been at 12dpiui 147; 15dpiui 527, 18dpiui 1889. (About 39 hours doubling time) The nurse said to call tomorrow afternoon to get both sets of results but I'm thinking I may call in the morning to get the Saturday update. My question is this: at what point do the numbers stop doubling in 48 hours? I'm worried that I'll get a "less than double" and freak out, even though it might be completely normal. I asked the nurse and she said that the numbers should still be doubling for the next few weeks, but she also said that we wouldn't be able to see anything on u/s until the numbers hit over 25,000 -- isn't that a little high??? I thought you could see the sack at 1000?? or maybe she's NOT talking about a vaginal u/s?? In any case, if you could give me some insight I'd really appreciate it. I am afraid to say it, but I actually have a pretty good feeling about this one, unlike the last two. The numbers are definitely looking better and we are wondering if there might even be more than one little bean in there! I'm just so anxious to have some confirmation that everything IS going well....Thanks for your help --
Jenn