A 20-year-old District of Columbia woman gave birth Tuesday to a baby carried full-term through pregnancy in her abdomen rather than her uterus-- the first such birth ever recorded at D.C. General Hospital.

Dr. John Gleason, acting chief of obstetrics and gynecology at the hospital, said such a condition may be as rare as one in every 15,000 pregnancies and all but 5 percent of those end in the death of the fetus.

The hospital refused to release the name of the woman, but said she is in good condition. Her 3.7-pound son is in "guarded condition," hospital officials said, but is improving.

Dr. Mehmur Abedin, who is in charge of the baby's care, said the infant's breathing is being augmented with a respirator, and he has some problems with his blood sugar level.

The baby's head is slightly misshappen, but physicians say they don't know at this time whether that results from the unusual pregnancy or a congenital problem.

"It's estimated that 50 percent of these babies have congenital malformations," said Gleason.

Particularly unusual was the woman's apparent lack of pain or discomfort until a week before her due date.

Doctors said it was impossible to determine precisely how and why the woman's particular pregnancy occurred.But they said in most such cases, conception occurs in a fallopian tube, rather than in the uterus. The embryo then attaches to the interior of the tube, and when the fetus becomes too large to remain in the tube, the tube bursts.

The fetus, inside the amniotic sac, is then expelled into the abdominal cavity, where it usually dies because it lacks a blood supply.

In this case, however, the sac attached to one of the ovaries and obtained a blood supply. For the remainder of the pregnancy, the baby lay in the right side of the abdominal cavity, outside the uterus. It was delivered by cesarean section.

Gleason said the woman's condition was not diagnosed until the last minute because she never complained of pain and there was no reason to suspect anything was wrong. The fact that she is "chunky," said Gleason, made an accurate diagnosis even more difficult.