My husband and I became pregnant before we were married. We went through the proper repentance and were sealed in the temple a year after we were married. The baby was stillborn (I was full term). She was not sealed to us in the temple sealing, will she still be ours in heaven? What about miscarriages, are those unborn babies still sealed to us?
The spirit enters the mortal body at some time before birth. That time has not been revealed in the scriptures. If the spirit had possessed the body of the stillborn infant, then that child will be resurrected and grow to maturity in its immortal state. If a miscarriage occurred before a spirit possessed the body, then no new life would have been created.
Membership records are normally not made out for stillborn children. If they are given names, they would be recorded in the family records rather than in the records of the church. To determine whether or not it would be possible to have the stillborn child sealed by proxy to the its parents, I would suggest that you consult with the president of the temple in your district.