CHICAGO - The latest advance in prenatal genetic testing purports to offer parents more detailed information than ever about the child they are expecting. But for some, the new answers could lead to another round of questions.

The technology allows doctors to detect small or subtle chromosomal changes in a fetus - such as missing or extra pieces of DNA - that could be missed by standard tests.

Most parents will get results confirming a normal pregnancy. But some will learn that their baby has a birth defect, a developmental problem or other medical condition, and in a small number of cases the test will detect things that no one knows quite how to interpret.

The information can allow parents to prepare for early intervention and treatment, but it also could raise questions about terminating the pregnancy or lead to nagging worry over uncertain results.

The Reproductive Genetics Institute in Chicago, which has helped pioneer the rapidly developing field of prenatal diagnosis and testing, recently began offering the procedure - array comparative genomic hybridization, or array CGH for short - to any pregnant woman who wants it.

"The technology has been available for a number of years . but it has almost never been used prenatally," said Dr. Norman Ginsberg, an obstetrician specializing in prenatal genetic testing at the institute. "We think this is the beginning of the next generation of how we'll look at things."

Other medical experts see the technology as promising but have concerns about using it as a first-line test because of the potential drawbacks and the lack of published research. The availability of array CGH also raises fundamental, sometimes delicate, questions for parents.

How much do they want to know about their child's genetic makeup before he is born? How will they deal with the uncertainty of some test results, such as detection of chromosomal changes that have not been associated with diseases? Should the technology be used to identify diseases in their children that would not emerge until adulthood?

"This technology is giving genetic counselors and physicians a challenge in that there is more to discuss with patients, and it gives patients a lot more to think about in terms of what kinds of information they want to know about their baby prior to delivery," said Jennifer Hoskovec, director of prenatal genetic counseling services at the University of Texas Medical School at Houston.

Array CGH is just one of the newer microarray technologies expected to become widely available to parents.

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Prenatal genetic test offers more information, raises questions

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