Within twenty-four hours of Mother's Day this year, a California appeals court held that E.G., a woman who gave birth to twins conceived with her lesbian lover's eggs, was the sole legal parent of those twins.

The ruling came as a terrible disappointment to K.M., whose eggs had been used to conceive the twins. K.M. had petitioned to establish her parental relationship with the children, but the trial court, affirmed by the appellate court, dismissed K.M.'s petition. The court based its conclusion largely on a consent form that K.M. signed, waiving parental rights prior to the retrieval of her eggs.

The decision in this case exposes the complexity of defining the term "mother" as well as the discriminatory impact that traditional default rules can have on a nontraditional family. (In the law, "default" rules are those that apply if the parties do not otherwise stipulate.)

For the remainder of the column, to make it easier to follow the identities of the parties, I will refer to E.G. as "Birtha" (since she is the birth mother) and to K.M. as "Ova" (because her ova gave rise to the twins).

Birtha and Ova were a couple when they decided to use Ova's eggs to try to conceive a child in 1995. A doctor at the fertility clinic where both women had been treated suggested that they use Ova's eggs and Birtha's womb to have children, because each woman suffered from medical problems that prevented one from becoming pregnant and the other from becoming a genetic parent.

The result of the chosen arrangement would be children that would have biological connections to both women. (Notably, this would create a variant on the classic family in which one person -- the father -- contributes genetic material and the other -- the mother -- contributes genetic material as well as gestates and gives birth to the child.)

Prior to retrieving her eggs, the hospital required Ova to sign a consent form that included, among other things, a waiver of parental rights to any resulting offspring. She signed the form -- as so many of us routinely do on request when we go into the hospital. Doubtless, she believed that without her signature, the procedure could not go forward.

When the twins were born, the two women were living together and proceeded to share the work of raising the children, work that is traditionally associated with mothers and fathers. As so many married couples do, however, this couple split up and eventually found itself in litigation over respective rights vis-a-vis the children.

The standard egg donation consent form that Ova signed at the hospital emerged as a very significant document in this litigation. The form contained a waiver of parental rights with respect to children resulting from any retrieved eggs.

Ironically, Ova apparently signed the form in order to facilitate the creation of children for whom she would in fact bear responsibilities and to whom she would maintain rights. Ova said that she planned to adopt the children later to formalize their relationship, though this statement was considered further proof that she understood that she was not their legal mother absent adoption.

But Ova acted like the children's mother in countless ways, actions that suggested that she wanted to be their mother but did not understand the law to protect that desire without an official adoption.

Ova likely thought, moreover, that she would stay with Birtha and live as one of two mothers of the twins and that the issue of "legal parent" would never be as important as the reality of her connection to the two children.

Though perhaps naïve, this is all a far cry from Ova's intending to give up her parental rights.

The premise of the consent form that Ova signed is that if someone other than the genetic mother gestates a child, then either the genetic or the gestational mother (but not both) will be the "real" legal mother. The presumed situation is therefore that a woman is donating her eggs to another woman who will then become the mother.

In practice, these implicit assumptions foster discrimination against same-sex couples. Paradoxically, for example, to permit the IVF to proceed according to plan, Ova had to sign a form that included a declaration of her intention to do precisely the opposite of what she apparently intended to do.

The California appellate court, however, pointed to the terms of the consent form as evidencing Ova's intention that Birtha be the sole legal parent, possessing all parental rights that Ova might otherwise have had. "The ultimate determination of natural motherhood," asserted the court, "depends not upon the existence of a binding contract but rather ... upon the woman's intention to bring about the birth of the child to raise as her own."

But can the court truly infer the absence of such an intention primarily from a signed default consent form?

Imagine the analogous male/female situation. Husband and Wife are a couple that wants the woman to become pregnant. Unable to conceive through sexual relations, the couple undergoes a course of In Vitro Fertilization (IVF).

When the doctors prepare to collect Husband's sperm, they ask him to sign a default consent form, one under which he relinquishes paternity rights over any resulting children. He signs the form, which also contains provisions indicating his understanding of the process of preparing the sperm for fertilizing his wife's eggs and the potential risks involved. The man and woman raise the resulting child until the age of seven, when they divorce.

It would be strange to say here that Husband had explicitly manifested his intention to relinquish paternity rights. Both his relationship with his spouse and his interactions with his children belie any such intention.

Of course, the idea that a father would, as a default matter, have to relinquish his paternity rights as part of fertility treatment for his wife is preposterous. Our default rule is that there can be both a mother and a father, not only one or the other.

When Husband and Wife in the real world conceive and bear a child in the conventional way, the various meanings of "mother" converge, and it is accordingly unnecessary for the law or society to articulate exactly what features define the essence of maternal status. The mother in such a case is the person who conceives, bears, and cares for the child.

Once a family departs from this picture, however, it is no longer possible to avoid the question. Is the woman whose egg is fertilized the mother? Is the woman who gives birth to a child the mother? Or alternatively, is the woman -- or are the women -- who care(s) for a baby the mother(s)?

There are circumstances in which we would answer "no" to each of these questions, although all three together conventionally define motherhood.

An egg donor, for example, like a sperm donor, can intentionally and prospectively relinquish contact and relations with her genetic progeny: the problem here is that Ova does not really seem to fit the "egg donor" role.

Similarly, a surrogate can decide to bear a child for someone else.

Finally, there are people who care for others' children, either as part of a support network or extended family, or as paid childcare. While these people may be valued caregivers, they do not ordinarily occupy the special status of "mother."

We can thus isolate each respective component of motherhood and determine that it is not the essential component. What this means is that defining the "essence" of motherhood through an across-the-board rule may not be desirable or even possible.

In some ways, it may seem that the most reliable, predictable, and thus legally sound result in the Birtha/Ova case is to place a great deal of weight, as the appellate court did, on the consent form that Ova signed. The legal significance of such a form is clear and unambiguous, and no one forced Ova to sign it.

But common sense pulls many of us in a different direction. The behavior of the two women -- who were in a committed relationship with each other at the time of conception -- supports an intention by both to become parents to the children to come.

To ignore this context and rule as the appellate court did, is to exhibit insufficient respect for the connection between the parties in this case. It is also to focus far too much attention on the very common willingness among many people to waive rights that they are asked to waive and that most people imagine will never be called into question because they trust their life partners.

It appears, based on the facts of this case, that Ova is a mother to the twins for whom she has cared with Birtha. Her desire to fill that role now must therefore come as no surprise to anyone following her story.

The case may ultimately go up to the California Supreme Court. And though a fact-sensitive inquiry is less neat and clean than the path taken by the appellate court here, it is nonetheless the wiser course.

It would be tragic to define "mother" by reference to oral or written waiver agreements (and, in this case, to some isolated comments by Ova that seem consistent with such an agreement -- comments that are concededly balanced by others that are flatly inconsistent with it). The injustice of proceeding in this fashion, moreover, would profoundly affect not only the person who has mothered the children in the past and wishes to do so in the future but also the children, who stand to lose as much in these legal battles as the named parties to the litigation.