A New Jersey judge has ruled that a gestational surrogate who gave birth to twin girls is their legal mother, even though she is not genetically related to them.

The ruling gives the woman, who carried the babies in an arrangement with her brother and his male spouse, the right to seek primary custody of the children at a trial in the spring.

The case illustrates the legal complexities of gestational surrogacy, in which a woman carries unrelated embryos created in a petri dish. A gestational surrogate in Michigan recently obtained custody of twins she carried, but courts in several other states have upheld the rights of people who contracted with gestational surrogates.

Prof. Charles P. Kindregan, an expert in reproductive technology law who teaches at Suffolk University Law School in Boston, said the New Jersey ruling, which was made Dec. 23 but released to the parties in the case this week, could expand the rights of gestational surrogates if it stood.

“;If it's upheld, that suggests that gestational surrogacy is not as different from traditional surrogacy as we've always interpreted it to be,”; Kindregan said.

Kindregan has worked with an American Bar Association committee in an effort to standardize surrogacy laws across the country.

In the New Jersey case, the surrogate, Angelia G. Robinson, agreed to have the children in 2006 for her brother, Donald Robinson Hollingsworth, an accountant in Manhattan, and his spouse, Sean Hollingsworth. The embryos were created from anonymous donor eggs and fertilized with sperm from Sean Hollingsworth.

The girls were born in October 2006 and went to live with the Hollingsworths at their home in Jersey City. But in March 2007 Robinson filed a lawsuit seeking custody, alleging that she had been coerced into the arrangement.

Judge Francis B. Schultz of Superior Court, who ruled in the case in Hudson County, N.J., relied heavily on the precedent established by the New Jersey Supreme Court in 1988 in the case of Baby M. The surrogate in that case, Mary Beth Whitehead, carried her own genetic child for another couple after artificial insemination with the man's sperm. After Whitehead decided that she wanted to keep the baby, the court ruled that her maternal rights could not be terminated against her will.

“;The surrogacy contract,”; the Baby M court found, “;is based on principles that are directly contrary to the objectives of our laws. It guarantees the separation of a child from its mother; it looks to adoption regardless of suitability; it totally ignores the child; it takes the child from the mother regardless of her wishes and maternal fitness.”;

Citing that passage, Schultz wrote, “;Would it really make any difference if the word 'gestational' was substituted for the word 'surrogacy' in the above quotation? I think not.”;

Robinson, of Keansburg, N.J., issued a statement calling the decision “;one more step in helping to insure stability and peace in the lives of our girls.”;

Robinson was represented by Harold J. Cassidy, a Shrewsbury, N.J., lawyer who also represented Whitehead. In a statement, Cassidy applauded the decision and called surrogacy “;an exploitation of women.”;

Alan S. Modlinger, the lawyer for Sean and Donald Hollingsworth, said the case was of importance to gay men and lesbians because of their reliance on reproductive technology to have children.

Since 2007, the twins have shuttled back and forth between the Hollingsworths' home and Robinson, who has three parenting days a week. A final decision on custody is expected after the trial this spring.