A 12-day-old baby, who had developed in his mother's abdomen instead of her uterus, has died, a hospital spokesman said yesterday.

At a press conference three days after the Sept. 5 birth at D. C. General Hospital, physicians had said they were optimistic about the infant's chances of survival, although it was having breathing difficulties.

But on Sept. 17 the baby died, apparently of a severe inflammation of the intestinal tract and bleeding, said hospital spokesman Mark Baron.

It is extremely rare for babies who developed outside the uterus to be born alive, and even rarer for them to be carried to term, as was this baby.

Physicians at the hospital said they had no idea, until about a week before delivery, that the 3-pound 7-ounce baby was not being carried in the normal manner.

Such pregnancies usually occur when a fetus begins to develop in a fallopian tube, rather than in the uterus. As the fetus grows, the tube expands, eventually bursting and expelling the developing fetus into the abdominal cavity.

In rare instances the sac surrounding the fetus then becomes attached to some part of the cavity and establishes a blood supply for the fetus. In this case, the sac was attached to one of the mother's ovaries.