Daring new operations on fetuses in the womb appear safe for the mother without endangering her chances of having more children but so far have failed to help most babies survive, researchers said.

Surgeons at the University of California in San Francisco, who have pioneered the new techniques, said Tuesday an evaluation of the first 17 operations shows the procedures offer promise, although the long-term survival of the fetuses remains low.The procedures involve partially removing fetuses from the womb through incisions in the abdomen, surgically repairing defects in their diaphragms, kidney, spines and elsewhere and returning the fetuses to the woman's body.

Although two women developed complications, none of the women died and there appeared to be no adverse effect on the women's fertility, the researchers said. Seven of the the women went on to have normal pregnancies and deliveries, and an eighth was pregnant.

"We conclude that (the procedures) can be accomplished without unduly endangering the mother's life or her future reproductive potential," the researchers wrote.

The researchers cautioned that more research should be done to improve the procedures, which cost $10,425 each on the average.