Babies Update

Just thought I'd share an update on the babies from this mornings ultrasound appt with the high-risk Dr.
(TMI alert!--so there, you've been warned :) ):
The babies are looking good! Everything looks good on the ultrasound (they're both very active!) and they're heart rates are perfect. They are both definitely GIRLS, so no more mystery there. :) And the Dr. said that they came from a single egg and sperm (not sure how he can tell that; and it's a little confusing because the ultrasound tech at my OBs office said they were from 2 different eggs, though that was several weeks ago), and judging by the thinness of the membrane between the babies and the fact that they share a placenta, they are almost positively IDENTICAL as well (heaven help me--I'm crossing fingers for a birthmark now ;) ).
The downside of the membrane being so thin is that there is a slight possibility that blood might be transferred between the babies through the membrane, causing there to be too much blood in one baby and too little in the other. However, they're currently measuring the same size (13 oz) and my cervix is double the normal size/thickness, so for now, things look good and the babies aren't going anywhere. The high risk Dr. is just going to have me come in regularly (my next appt is in 3 weeks) to check and make sure that the babies and my cervix still look good.
 The Dr. also said that HALF of twins are born before 34 weeks, so if we get to 34 weeks that's great. So, I guess there's a very good chance these little ones will come in December and we'll just shoot to have everything ready for them to come in the next month or so. Anyways, bottom line, the babies look good right now and so do I, and we'll just be keeping a close eye on everything.