Australian doctors report the first successful human pregnancy using eggs that were deep-frozen, thawed and fertilized in the laboratory, an approach that could have major implications for "test-tube" baby programs around the world.

Dr. Christopher Chen, of Flinders University of South Australia in Adelaide, said that a previously infertile 29-year-old patient is now more than six months pregnant with twins after using his experimental method.

The pregnancy is "progressing satisfactorily," he wrote in the April 19 issue of the British medical journal Lancet. His colleague, Dr. Warren Jones, said last night in a telephone interview that the pregnancy is going "normally" and that the babies are due in early July.

Chen predicted that the availability of a successful approach for freezing and thawing eggs could eventually lead to egg "banking" for women, much as male sperm banking has long been available.

"If this can be reproduced reliably, it's a major breakthrough because of the advantages it offers in protecting the moral sensitivities of our society while giving improved medical services to infertile couples," said Dr. Gary Hodgen, scientific director of the Jones Institute for Reproductive Medicine at the Eastern Virginia Medical School in Norfolk.

He said that the ability to freeze and thaw eggs could help improve the short-term options for infertile women and allow new reproductive opportunities for others, such as women who want to postpone pregnancy for career or medical reasons but to have children later.

For instance, he said, a young woman undergoing treatment for cancer or other illnesses that might damage her eggs could elect to store them for a possible later pregnancy.

Chen also noted that the handling of fresh and frozen human embryos in the laboratory has led to "complex ethical, social, legal, moral and religious issues" that could be overcome with the use of frozen, unfertilized eggs. There was widespread publicity in 1984, for example, about the uncertain fate of frozen embryos left behind in Australia by an American couple who died.

Since the birth of the first test-tube baby in England in 1978, Hodgen estimated that more than 3,000 babies have been born worldwide, including 199 in the well-known Norfolk program, using "in vitro fertilization" techniques. Most involve the use of drugs to stimulate production of eggs in a woman's ovaries, removal of the eggs, fertilization in the laboratory and implantation of resulting embryos in her uterus.

Since about seven eggs can be removed at a time, doctors have faced a dilemma about how to handle surplus ones. If too many are fertilized and implanted, there is a greater chance of difficult multiple births -- triplets or even quadruplets. But there is also concern about what to do if they are not implanted.

Australians, particularly a team at Monash University in Melbourne, have pioneered frozen embryos as one option, but this too has run into technical and ethical difficulties. Hodgen said that about 15 babies have been delivered and about a dozen pregnancies are in progress worldwide resulting from thawed embryos.

In the United States, the first such birth is expected in a few months at a University of Southern California hospital, Hodgen said. The Norfolk group has not attempted freezing techniques thus far, he said, and has instead opted for a new program in which patients donate surplus eggs to other patients.

Freezing human eggs has long been considered desirable, said Hodgen, but the eggs have proven far more fragile than embryos and have generally been destroyed in the freezing process.

Chen wrote that his approach, involving slow freezing and rapid thawing of the egg, appears to be successful for both mouse and human eggs. He acknowledged concern about potentially damaging effects on the offspring, but said that most of the eggs survived thawing and appeared to fertilize normally.

In the Australian pregnancy, three eggs were thawed six hours after freezing and later fertilized and put in the patient's uterus. Heart activity indicating "a healthy twin" pregnancy was confirmed by ultrasound, the Lancet report said.

Jones said last night that the patient had declined to undergo genetic testing on the unborn infants, but that doctors were reassured by animal tests that the procedure did not appear to pose developmental problems.