'HAPPY MOTHER'S DAY," chimed the nurse as she woke me for temperature and blood pressure readings instead of breakfast in bed.

I cringed. They had forgotten that although I was on a maternity floor, I was not a mother yet. I was eight months pregnant, to be sure, and, if that weekend's tests turned out a certain way I might become one that week. But the babe-to-be was still hiccuping in my belly instead of crying in my arms -- and that was all the difference.

But was the nurse really off base? When the afternoon visiting hours came, Ted my 11-year-old stepson, arrived with a card and a baby book he and his father had picked out downstairs. "Happy Mother's Day," they said, and we celebrated as long as the hospital would allow.

After they left, I opened the book to study it more closely. They still drew family trees, I noted, with only two squares for each set of parents and grandparents. That's all I needed for this one, but in Ted's case, one set of his grandparents had divorced and remarried and dotted lines and new squares had had to be sketched into his baby book. A dotted line and square for my name had not been added.

The book, which his mother had maintained with great care, had passed to his father when he was awarded custody of his five-year-old. The handwriting shifts for the first grade report, as his father noted briefly that his mother had moved to Tampa and that Ted was doing well in school and seemed to have adjusted to the divorce.

I joined their household two years later, long enough for a strong friendship to be forged between father and son. We were married six months later, waiting until Ted returned from summer vacation with his mother so that he could serve as best man.

He called me "Sara" at the start. His father felt it was important to refer to his mother as "Mom," to keep her as a real person in his life, and I agreed.

But it was hard at the start. You think of 7-year-olds as little people still growing up -- which they are -- but move in with one and you'll find that they're pretty set in their ways. You can chisel off the rough edges of the manners that annoy you, shape the rules to try to provide some sort of harmony for everyone, give them praise and punishment, love, and, maybe, get some in return. But the bottom line is that he will always be someone else's child, someone who carried him, bore him, breastfed him, stimulated those little brain cells, responded to his cries. Someone who could take him away if your spouse should die.

In some ways, I can enjoy him more because of that. With less of my own ego tied up in his genes, perhaps the bumps don't come as hard, perhaps I don't push him as hard as I might otherwise.

Yet I would get a small sense of pleasure when I would hear the little boy tell his friends, "My mom did this." And I smile now remembering the time he broke up an argument between my husband and me by saying, "Don't fight, you two. I don't want to have to visit two mothers every summer."

Before Steve was born two years ago, I suggested to his father that it might be time for him to start refering to me as "Mom" when he was talking to Ted. I was afraid my toddler's first words might be "Sara" rather than "Mama." The message got to Ted, who now calls two women "Mom" to their face (and Lord knows what behind their backs).

But what does that word mean anyway? I have but one mother to remember today -- but in these days of "significant others" and "yours, mine and ours," who's to say who should really get the cards and flowers and breakfasts in bed? I will always be Steve's mother: I carried him and bore him and breastfed him and have changed countless dirty diapers. But maybe I should take the day to salute the wonderful women who have watched him since I returned to work, the one who witnessed what was probably his first step, the one who taught him to give kisses when asked in Spanish. I'll always agonize over what my working has meant to him, just as Ted's mother probably agonizes over what her departure has meant to her son.

I don't remind Ted about Mother's Day -- I consider that a bit of a conflict of interest. But I'm often the one who ends up reminding him that his mother's birthday is coming up.

After all, what's a mother for?