SANTA ANA, CALIF., AUG. 14 -- A surrogate mother carrying a couple's test-tube baby is suing for custody of the child in a case that could redefine parenthood.

"There's nothing negotiable about it. This is my baby," declared Anna Johnson, 29, who filed suit in state court Monday for custody of the child on grounds that the biological parents would not provide a good home.

Mark and Crispina Calvert provided the sperm and egg to create the embryo that was transferred from a lab dish to Johnson's womb under a $10,000 agreement with Johnson. The baby is due in two months.

Johnson's effort to pursue custody of a baby that has no biological relation to her is unprecedented, said the Calverts' attorney, Christian Van Deusen.

The case differs from the landmark Baby M custody case in New Jersey. In that case, the child was conceived with a surrogate mother's egg and the sperm of a man hiring her. The man's wife had no biological ties to the child.

Van Deusen and Johnson's attorney, Richard C. Gilbert, agreed the Johnson case will focus on what constitutes parenthood. Although California law presumes the birth mother is the legal parent, a judge has leeway, Gilbert said.

Johnson, a single parent of a 3-year-old, maintained today on ABC's "Good Morning America" that she has biological and maternal bonds with the fetus. "The baby, while it's growing inside me, has my cells and my blood nurturing this child, maintaining its life," she said.

Johnson, who is on disability because of pregnancy complications, also seeks child support and damages for emotional distress. She said she decided to seek custody because she believes the Calverts showed disregard for her complications and gave the impression they might not want the baby.

The Calverts denied Johnson's allegations that they ignored her medical needs, failed to make timely payments or lost interest in the pregnancy.