found heart beat for twin A but not twin B

HI, WENT TO THE DOCTORS 3 WEEKS AGO MEASURED 4 WEEKS 5 DAYS AND SHE SAID THERE WAS 1 SAC, TODAY (EXACTLY 3 WEEKS LATER)I WENT AND SHE FOUND TWINS!BABY A WAS MEASURING 7 WEEKS 2 DAYS AND HAD A HEARTBEAT BUT BABY B WAS SMALL AND SHE COULD NOT FIND A HEART BEAT OR POLE OR YOLK SAC, SHE SAID IF BABY B DOESN'T REABSORB BABY A WILL MISCARRY TOO.COULD BOTH MY BABIES LIVE?HAS THIS HAPPENED WITH A GOOD OUTCOME OF TWINS and  found a heartbeat later)?

[AnnieBrooke]

If they are identical twins, the outcome is more problematic than if they are fraternal twins.  Identicals can be connected to each other in some ways and have no protection against something called twin-to-twin transfusion.  If they were fraternals, one can fade and the other will not be affected, as each has its own sac and placenta, and they are not connected to each other in any way.  

At this point, if they are identical and twin A has a heartbeat and twin B does not have a heartbeat, pole or yolk sac, there is no possible heartbeat to come for twin B.  The difference in development shows that (if they are identical, and therefore began at exactly the same time) twin B is done developing.  There would be no sudden leap to catch up or anything -- embryos add so many millions of cells a day that this much of a gap means it is all over for twin B.  I'm sorry.

The good news is, if the second twin is larger by that much and has a heart beat, it sounds like the two were not connected to each other that much even if they were identicals (or twin A would not be continuing now either).  If they were identicals but each had its own amniotic sac and its own placenta, the loss of twin B would not be so likely to harm twin A.  Given the differential of size and development, it sounds like (if they are identicals) twin A is not that affected by twin B, a good thing.

Google "twin to twin transfusion" for more information on how one identical twin can affect the other.  I lost twins due to this and it was very hard to become aware that one had been all right and the other's failure had caused its loss.  However, your scenario sounds a little more positive because you have one gone and the other going on.  If they are fraternals, your body does not in fact need to re-absorb the lost embryo for the other one to go along fine.  That is called "vanishing twin," and you can even go on for quite a while with the little separate sac and tissue showing up on your ultrasounds and it really does not affect the other baby at all.

Good luck and keep us posted.