It's a King Solomon tale with a 21st century twist -- two women battling in court over the same children.

Science says both women are the biological mothers of 7-year-old fraternal twins -- one provided the eggs, the other carried the girls to term. And the women raised the twins as a couple until they broke up nearly two years ago.

While science sees it one way, the courts see it another and so far have awarded parental rights and custody solely to the birth mother.

But come January, the issue lands in the lap of the California Court of Appeal, and observers say the court's ruling could have far-reaching implications for lesbian rights, in vitro fertilization and parental custody laws.

The appeal stems from a ruling in October, when Marin County Superior Court Commissioner Randolph Heubach found that the egg donor had made an express promise before the babies were born that her partner would be the sole mother.

She even signed a hospital document waiving her right as a parent. For that reason, Heubach ruled that the donor, identified in court records only as K.M., had no standing. (To protect the privacy of children, family court does not release the full names of parties involved in cases.)

K.M. is challenging that ruling to the First District Court of Appeal in San Francisco. And Dr. Marcelle Cedars, director for the Center for Reproductive Health at UC San Francisco, where K.M. and her partner E.G. were patients, is closely watching to see what the appeals court does.

"It's unfortunate that one of the problems with our specialty is that it presents complex issues without a societal road map," she said. "The outcome of this case may better prepare us for these types of issues in the future."

On a day in 1995, K.M. sat in a reception room at the UCSF clinic waiting to have her eggs harvested for the in vitro procedure. An administrator handed her a clipboard with a few routine documents, including information about her medical history, to sign. At the bottom of the stack was a form waiving her right as a parent. K.M. says she unthinkingly signed it.

Her partner had been trying to get pregnant for some time and couldn't produce eggs, K.M. said. Because of fibroid cysts on her uterus, K.M. wasn't able to carry a child. So the women's doctors suggested that E.G. consider in vitro fertilization with her partner's ovum, said K.M.'s attorney, Jill Hersh of San Francisco. And the women agreed.

"We were so involved in the process that when you're told to sign something, you do it," K.M. said the other day, referring to the waiver. "We were planning our life with children and not thinking that we would ever break up."

The women met in 1992, moved in with each other two years later and registered with the city of San Francisco as domestic partners. By the next year, they were turning the dining room in their one-bedroom flat into a nursery, painting baby furniture and picking out wall colors. They were also searching for a larger house to buy for their new family, which they eventually purchased in Marin County.

When the babies were born four weeks prematurely, the couple stayed with them in the hospital around the clock, K.M. said. On one of those days the women managed to break away for a few hours, walked over to the gift center and purchased wedding rings. They exchanged them on Christmas day.

"It was the most significant time in our relationship," said K.M. , a 42- year-old president of a nonprofit organization. "We were having a family, and were bringing our girls home."

During the next six years, the girls grew up in Marin County surrounded by friends and family. They collected American Girl dolls, watched the television show "Lizzie McGuire" and called both women "momma." But by 2001, the relationship had grown rocky and the birth mother, who declined to be interviewed for this article, moved with the twins to Massachusetts.

"Slowly but surely she began limiting my contact with my daughters," K.M. said.

After she sued to be recognized as a legal parent and lost, K.M.'s contact with her daughters was curtailed. Her former partner, E.G., disconnected her phone in Massachusetts, K.M. said. Even when she is allowed to have brief visits with the girls, K.M. said, the meetings are painful.

"From the moment we're together, we have to anticipate saying goodbye," she said as her eyes welled up with tears.

But the birth mother's attorney, Diana Richmond, tells a different story. Richmond says that at least two months prior to the pregnancy, E.G. and K.M. agreed that her client would be the sole mother. During the trial in Marin Superior Court, the birth mother testified: "I told her that I would not be willing to consider an adoption until five years after the children were born because I didn't know her well enough. The relationship was too young. I didn't want to be in a custody battle."

Richmond acknowledged that her client wants to limit the relationship between K.M. and the twins, who will turn 8 this month. K.M. has gone back on her word, the lawyer said, and "there is no trust left."

In some ways, K.M. blames the clinic for the mess. She says the couple's doctors knew they were in a committed relationship, yet no one told her about the waiver form or counseled her on its ramifications.

"Because my client is in a nontraditional relationship, she wasn't the institutional center's idea of a traditional parent," said Hersh, K.M.'s attorney. "That's why we're here today."

Hersh argues that even if the law holds the consent document as a binding contract, K.M. should share legal rights because she helped raise the children from birth until the breakup.

The National Center for Lesbian Rights agrees. Lawyers for the organization have filed a legal brief arguing on behalf of K.M.

"What governs the legal parentage of a child born as a result of a medical procedure is the actual intent of the people involved," said Courtney Joslin, an attorney with the group.

She says the fact that K.M. remained in the home and reared the girls wipes away any contract she may have signed.

Cedars, who was not at the fertility center when the women were patients there, said that even if K.M. had signed away her rights to her children before they were born, it only stands to reason that she would want those rights back. It's not just a biological issue, she said, but an emotional bonding. Cedars said that in the 2 1/2 years she has been at the clinic, it has not required lesbian couples to sign the donor form that K.M. was given. And if she had been there when K.M. and E.G. were patients, she likely would have turned them away.

"I would have problems with a donor who signed away her rights but had an intent to rear the children," she said. "It's a disconnect. I think if it's your eggs and you reared the child for nearly seven years, who can say who has the greater legal bond."

Hersh says she's optimistic that the higher court will rule in their favor.

"We're hoping the ruling advances the law so that the children of gay families have the same legal protection as the children of heterosexual families."

In the meantime, K.M. hopes for the best but is prepared for the worst.

"I know that for nothing else the girls will turn 18 in 10 years, and I will keep this up until then," she said. "I know that in their heart of hearts they know that we will be reunited at some point."