We just got back from the second ultrasound. The embyro is doing well, measuring 7 weeks 5 days and with a heartbeat of 154. There is a slight sac separation, which our doctor doesn't think is a cause for concern, and there is still the second empty sac, ditto. I'm still a little bummed about not getting twins this time around, but I'm really happy about the good measurements. My body seems to have a one-baby-per-pregnancy rule or something. We have officially graduated to a regular OB.