When I was 4, my mom announced that she was pregnant. I was ecstatic -- finally I'd have the little brother I'd always wanted. There was no doubt in my child-mind that the baby would be a boy. My parents already had a girl, so why would they need another one? I just assumed they would ask the baby gods for a boy and be granted their wish.

Needless to say, when my sister was born, I was devastated. I had been replaced by a gurgling bundle of joy who, by all accounts, had the rosy cheeks and ringlets of an earthbound angel. I couldn't hack the competition. I packed my suitcase and tearily headed out the door, a self-proclaimed orphan.

I eventually got over my replacement complex and learned to love my little sister. A natural selection was made and now I can't imagine life without her. But for those older siblings -- and parents-to-be -- who want to challenge nature, a formidable weapon is at hand. Last week, doctors at the Genetics & IVF Institute in Fairfax, Va., led by Dr. Edward Fugger, announced that they can sort sperm in such a way that will allow couples to choose the sex of their babies. But how ethical is gender selection, and is it safe?

Couples who entered the trial either wanted to prevent sex-linked disorders or simply wanted to do a little gender balancing within the family. In fact, 90.5 percent of the study's participants had already given birth to two or three sons and wanted their final child to be a daughter.

Using a process called flow cytometric separation -- branded MicroSort -- doctors were able to increase the number of X-chromosomes (female) in any given sorted sperm sample to 85 percent, vs. the approximately 50 percent contained in a normal sperm specimen. That means that couples who use a sorted sperm sample are five to six times more likely to have a female child than a male child. A total of 29 pregnancies by intrauterine insemination (IUI), in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) resulted during the trial. Of the 14 pregnancies in which the gender of the fetus or child has been determined, 13 are female. That's a 92.9 percent success rate. The Amazon women's lost civilization has a chance at resurrection yet.

For couples who run the risk of passing on genetic, sex-linked diseases to their children, gender selection is a boon. Disorders like hemophilia and muscular dystrophy, two diseases most prevalent among males, could be avoided by tilting the content of a man's sperm to favor the X chromosome. Here the request for sex selection is justified for health reasons. But for people who simply desire to give birth to one gender over another, the ethical lines become blurry. If you're religious, fooling with nature goes against the domain of God; if you're not, you might get a thrill out of cheating Lady Luck. While it might seem fun to predetermine the sex of your baby, the bottom line is that sex selection could theoretically lead to the demise of the human race. If too many people choose one gender over another, we could be in big trouble.

But it depends on how many people really want to select their child's gender, says Dr. Alan DeCherney, chairman of the Department of Obstetrics and Gynecology at UCLA. His feeling is that not a lot of people really want to interfere with nature, at least not in the United States. But what about people in other countries, like China, where male babies are historically more valued than female ones? Well, the MicroSort study won't be of much use to Chinese couples since the only conclusive data shows that sperm can be sorted for female selection, not male. Unpublished data shows that the MicroSort technology can increase the average content of Y-bearing sperm to 65 percent from the normal 50 percent. However, this theory has not been fully tested.

In addition to the ethical questions surrounding gender selection, there's also the issue of whether the flow cytometric separation of sperm cells is a safe process. To date, the only way to tell the difference between living X- and Y-bearing sperm is by their total DNA content: X chromosomes have 2.8 percent more DNA content than Y chromosomes. In order to sort the sperm, fresh and frozen samples are liquefied, then evaluated for volume, count, motion, development, viability and percent of abnormal cells using World Health Organization standards. Samples are then extended, centrifuged, resuspended and filtered through glass wool to remove debris and bum cells (good thing they don't do this while the sperm's still in its natural environment). They are then stained with a fluorescent substance that finds female chromosome-bearing sperm cells according to their weight and marks them with a pink spot. To see the different sperm, the sample is exposed to ultraviolet rays and passed through a fluorescence activated cell sorter.

The potential danger lies with the process of staining the sperm and then exposing them to a laser. Some geneticists are concerned that the substance used to mark sperm cells could cause genetic mutations in those cells. And piercing sperm with a laser might nick the DNA. While this is the first time the MicroSort technology has been applied to humans, according to the report, all the resulting births so far have been of normal, healthy babies. Now we can finally join the illustrious ranks of the bovine, swine, ovine and rabbit, all unwitting test subjects in the name of human sex selection. More than 400 normal offspring were produced by these four animal species before the process was used with humans.

So if you're a mom who loves her little boys but yearns for a daughter, you might be interested in undergoing the MicroSort treatment. In that case, get ready to pay up. The Genetics & IVF Institute is currently the only place where the process is available, and it charges approximately $1,600 per cycle, according to DeCherney. A cycle is defined as an attempt to become pregnant via IUI, IVF or ICSI. The number of cycles it takes any one individual to conceive depends on several factors, including age, type of insemination procedure and quality of the semen specimen. The average age of the couples in the study was 33.9 years and the most successful method of insemination was IUI. Just make sure your stud doesn't deplete his sperm count by wearing tighty-whiteys, and a daughter is practically guaranteed.