One Maybe Two

We had our first ultrasound last week and I'm still a little in shock.  We had 2 sacs, but could only see 1 baby and 1 heartbeat in one of the sacs.  The empty sac looked a lot smaller than the other one.  We are not sure if it's a sac that didn't develop or we just couldn't see anything yet because it's so early.  I would have been about 6 weeks and 3 days at that point.  So the doctor said there is a 50/50 chance we are having twins!  I didn't expect that, but I'm excited.  It took a few days for the news to settle in and next week we'll know for sure if it's twins or just one.  I was relieved to see at least one heartbeat but am a little concerned about the empty sac.  This is going to be a long week waiting for the next ultrasound.