Allison is suddenly upon me like a sunburst, hurling herself into my lap, throwing her arms around my neck. "My mommy," she says to no one in particular. Before I can return her hug, she is off again, racing to the slide in a blur of swinging limbs and pigtails.

Along with the usual rush of love, gratitude, and exquisite pleasure that such a scene evokes in me, I feel a tug, a gnawing worry in my gut. Allison has just turned three years old — that age when kids suddenly know everything, the age when they're putting it all together, the age, so I'm told, that she might ask if she grew in my tummy.

She's used to the word "adopted," of course. "Read the Allison book!" she commands, pointing to the small photo album on her shelf. The first picture shows my husband, Jay, and me in full wedding regalia. "Mommy and Daddy loved each other so much they decided to get married," I say. "They were very happy except that they didn't have a baby." (Sigh, pause, turn to the picture of Allison at four days.) "Then, they adopted Allison! And they kissed her and hugged her because she was their little girl!" It continues with pictures of Baby Allison with relatives who are overjoyed to welcome her into the family.

The book leaves out a few things — like how she had a birth mother and father, a whole biological family tree. She did grow in a mother's tummy; it just wasn't mine. She was someone else's baby for nine months in utero and three days in the hospital. In some ways, she will always be someone else's daughter as well as mine: in the angle of her cheek or the golden softness of her hair — even in aspects of her dazzling personality. I find myself worrying about how it will be when it dawns on Allison that I am not her mother in quite the same way that other children's mothers are.

What am I afraid of exactly? I guess I worry that her budding understanding of what it means to be adopted will somehow alter the way she sees me. Right now, "Mommy" is the name on her lips as she falls asleep, the one she calls as she awakes, the one she shouts, with a running leap into my arms, when I come to pick her up from preschool.

Will it be a shock? Will she study my face when she thinks I don't see and long for that other who gave her life but could not stay to watch her grow? Will she shout at me, in the heat of adolescent rage, "You're not my real mother!" as my friend Marci, an adult adoptee, once said to her mother? Am I only the interim caretaker until the day, amid tears and applause, that she meets her birth mother on Oprah and waltzes off with her, arm in arm into the sunset?

And then I think of the evolution of my feelings for my daughter, Allison. It wasn't that long ago that the thought of adopting a stranger's infant plunged me even deeper into the despair that was my constant companion during my losing battle with infertility. And even when I realized that it was more important to me to love and nurture a child than it was to give birth, some part of me still protested.

"She has her father's chin," said Allison's birth mother as she, Jay, and I looked through the nursery window at her tiny daughter, soon to be ours. "I want a baby with Jay's chin!" was the rebel wail I choked back down my throat.

A few weeks later, emerging from that new-parent time warp when you wouldn't notice war breaking out, I knew that I was hopelessly smitten and forever changed. Yet the thought came to me, unbidden and slightly shameful: "I'm mothering someone else's baby." Sometimes I felt myself an imposter. "Your baby looks just like you," someone would say. "Isn't that something?" I'd reply. "She's adopted."

Then came that watershed moment when her birth parents were due in town for a court appearance to relinquish their parental rights. My fantasies ran wild, and I woke up in a cold sweat. "She is meant to be with me!" I shouted at the night demons. The moment I allowed myself to think of something going wrong with the adoption was the moment I realized how fully I felt myself to be Allison's mother.

And now my attachment is so fierce it takes my breath away. I have rocked her for a thousand hours, kissed 10,000 boo-boos, answered a million "whys." We have giggled uproariously at funny things and snuggled together until we fall asleep. We have survived the terrible twos, and we will survive the terrible tweens. She is my daughter. While I still feel a pang when I hear a woman tell her labor and delivery story, I jump right in when the talk turns to the intensity of the mother-child bond.

Perhaps an adoptive parent faces sooner what every parent must face eventually: Our children are not ours; they belong to themselves. What will keep them visiting us joyfully when they are grown is the quality of our relationship, not biology. And so it comes to me with a soothing simplicity: I should trust my bond with Allison. To adopt means "to take as one's own." If I can love another woman's child as my own, why would I think it might be different for Allison?

"Your daughter looks just like you," someone stops me in the street to say. "Thank you," I answer.

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