Once they decided to have children, Michel and Carl Meissner tackled the next big issue: Should they try to have a girl?

It was no small matter. Michel's brother had become blind from a hereditary condition in his early 20s, and the Meissners had learned that the condition is a disorder passed from mothers to sons. If they had a boy, he would have a 50% chance of having the condition. A girl would be unaffected.

The New Hampshire couple's inquiries about gender selection led them in 1999 to Fairfax, Va., where a new sperm-separation technique, called MicroSort, was under investigation. The couple's first attempt at artificial insemination, using sperm sorted by sex chromosome, was a failure. But on the second attempt a few months later, Michel became pregnant and gave birth to a daughter. They will try to have a second daughter using the technique later this year.

"I probably would not have had children if not for MicroSort," she said. "This was pretty much our only option for kids."

The technique separates sperm into two groups—those that carry the X-chromosome which leads to a female baby and those that carry the Y-chromosome which produces a male baby. The process was developed in the early 1990s by the Genetics & IVF Institute in Fairfax, and last week's opening of a MicroSort laboratory in Laguna Hills marks the company's first expansion.

"We believe the number of people who want this technology is greater than those who have access to it," said Dr. Keith L. Blauer, the company's clinical director.

The expansion brings with it not only a seemingly effective way to select a child's gender it also highlights a host of ethical and practical considerations that accompany sex selection, especially for the majority of families who use the technique for non-medical reasons.

The Laguna Hills clinic, which is a joint effort with the Huntington Reproductive Center of Southern California, offers sex selection for two purposes: to help couples avoid passing on a gender-linked genetic disease and to allow families who already have a child of one gender "balance" their families by having a baby of the opposite sex.

Blauer said that company has had an impressive success rate: 91 per cent of the women who become pregnant after sorting for a girl are successful, while 76 per cent who sort for a boy and get pregnant are successful.

The technique separate sperm based on the fact that the X-chromosome is larger than the Y-chromosome. A machine is used to distinguish the size differences and sort the sperm accordingly.