Suddenly, it seems the biological clock of motherhood may keep on ticking forever. "Women bear babies after menopause," announced the headline. Historic, exclaimed the pundits. Now, women can be more like men and presumably have children well into their dotage.

For many women, especially those who are just seeing their children take their first steps out of the nest, this is not necessarily a cause for rejoicing. But for a growing group of older women who desperately want a baby, the news is nothing short of a medical miracle. Until now, menopause has been an insurmountable barrier to fertility. It is a time, usually starting in their forties, when the ovaries stop releasing eggs and women are at last free or bereft -- depending on the viewpoint -- of the possibility of giving birth. But now, the New England Journal of Medicine tells us, older women can get pregnant and deliver a child.

In the journal's study, four of seven menopausal women gave birth to healthy babies. They did it by using standard in vitro fertilization techniques, getting eggs from younger fertile women. The donor eggs were mixed in the laboratory with sperm of the husbands of the menopausal women and then implanted into the older women.

One of the immediate problems here is that by this technique the mothers were not genetically related to the infants. They were simply birth mothers, or "host uteruses" in the jargon of high-tech procreation. They were pregnant all right, but the pregnancy came about through the use of another woman's egg.

This oddity of high-tech-manipulated nature is a medical miracle for some, but it is a legal nightmare for others. Just how nightmarish was revealed last week in California. An Orange County Superior Court judge denied a woman parental rights and custody of the child she had carried in her womb and to whom she had given birth. She, too, was a birth mother and used the same techniques that enabled menopausal women to become mothers -- but the judge decided that motherhood belonged to the egg donor, not the host uterus.

In this case, Anna L. Johnson, 29, had an embryo implanted in her uterus, and on Sept. 19 she delivered a 6-pound, 10-ounce baby boy. The egg came from Crispina Calvert, 36, and it was fertilized by Calvert's husband, Mark. Like the menopausal moms, Johnson has no genetic link to the infant she produced.

But unlike the menopausal moms, Johnson was paid to be a surrogate and agreed to carry the Calverts' child for a price. Similar to the wet nurse in times past, Johnson was hired as a kind of fetal nanny to take care of another woman's fertilized egg until it was ready to leave the womb.

This is not exactly what the conventional stork had in mind about having a baby. But there is nothing conventional about high-tech procreation. In the decade since the first test-tube baby was born, medical advances have scrambled beyond recognition the boundaries of parenthood and family relationships.

In the courts, new-age reproductive techniques have resurrected Solomon's ancient question: Who is the baby's real mother? In the 1988 case of Baby M, the surrogate mother, who was artificially inseminated with the father's sperm, was genetically linked to the child. Nevertheless, the New Jersey Supreme Court granted custody to the contracting parents while allowing the surrogate mother only visiting rights.

Now, the question of motherhood is further redefined: What happens when the egg comes from one woman, the uterus from another? Gene Mom vs. Birth Mom?

"It obviously poses all kinds of legal puzzles, which no one quite anticipated," says Daniel Callahan, director of the Hastings Center, a private bioethics institute in Briarcliff Manor, N.Y. "As the technology moves along, there'll be more cases. We are developing a different notion of parenthood."

It's not only in the courts that traditional family relationships are being turned on their head. Ricki Bingham of Hyattsville, Md., has already discovered just how different the notion of parenthood can be. At 40, she is undergoing premature menopause. She is also three months pregnant. Using the same techniques that enable other menopausal mothers to get pregnant, Bingham is carrying an egg fertilized by her husband. But in this case, she has some genetic connection. The donor egg comes from her younger sister, 30. "I was lucky," she says. "My three sisters offered eggs; two offered to be surrogates."

Even though it is all in the family, the "egg donor" and the "host uterus" and their husbands have had the benefit of counseling. "It's important if there are areas of concern or conflict that you deal with them early," says Bingham. What feelings or rights would the sister have once her eggs were donated to Bingham? If there were more fertilized eggs than needed, what would happen to these pre-persons-in-a-petri-dish? Would they be frozen? Discarded? What if the sister got pregnant during this period?

The questions don't stop at the birth of the child, whose aunt is also the genetic mother and whose mother is genetically an aunt. If Bingham's sister were pregnant, too, that child would be both a first cousin and half-sibling to the Bingham child.

The technology opens up a whole new medical arena of family responsibilities -- and family guilt. Just as relatives are now asked to donate lifesaving organs, such as a kidney or bone marrow, to relatives in need, are they now obligated to donate eggs to help others have children?

High-tech procreation is likely to continue. Young women planning to combine a career with having a family might well freeze their eggs now -- when the eggs are at their peak -- and implant them later.

It all comes down to a passionate longing for a baby. "I wanted a child," says Bingham. "I wanted to be pregnant. I was willing to go to whatever length to do this. The technology happened at the right time. Five years ago, I wouldn't have had a chance."