(CNN) -- Matthew and Beth Mandolesi told their doctor that they would be happy with a boy or a girl but wondered if there was a way to increase the odds that it would be a boy.Five years later, they are the parents of two boys, Antonio and Angelo.The Mandolesi family is part of a growing trend called "family balancing" that allows couples to choose their baby's gender, fertility doctors around the country say."A few years ago I had a couple of clients asking every month; now it's at least two or three a week asking seriously about it," said Dr. Kevin Winslow of the Florida Institute for Reproductive Medicine.There are three methods of gender selection. The cost, technology and price vary.The first and the oldest type is sperm separation, which has been used since the 1970s. The method that Matthew and Beth Mandolesi chose gave them about a 60 percent chance of having a boy, according to their fertility doctor.A sample of Matthew's sperm was spun in a centrifuge. The spinning separates the Y sperm that creates a boy from the X sperm that creates a girl. The Y sperm was used to fertilize Beth's egg.The couple paid $250, in addition to the cost of an in vitro fertilization procedure. The average sperm sorting costs $400 to $600 today, Winslow said.A more sophisticated type of sperm sorting is based on staining and separating sperm. MicroSort, from the Genetics & IVF Institute of Fairfax, Virginia, has been in clinical trials since 1995, hoping to gain approval from the Food and Drug Administration. It claims 76 percent accuracy for boys and 91 percent accuracy for girls.Right now, couples are enlisting in the trial and paying around $2,500 to use this unapproved technology.The newest and most controversial method is called pre-implantation genetic diagnosis, or PGD, and is based on embryo examination.This method requires in vitro fertilization. It's 99 percent effective and costs up to $19,000, said Dr. Jeffrey Steinberg of the Fertility Institutes, whose clinics in Los Angeles, California; Las Vegas, Nevada; and Mexico provide sex selection through various methods, including PGD.PGD was first developed and is used primarily to find genetic mutations linked to about 200 genetic diseases such as Tay-Sachs and cystic fibrosis.Eggs are taken from the woman and fertilized with sperm to form an embryo. Doctors then take one cell out to analyze its DNA. The healthy embryos are selected, and then female or male embryos can be chosen.Some ethicists and doctors say they are troubled by PGD being used for elective, nonmedical reasons.Dr. Mark Hughes, a pioneer in PGD and director of the Michigan-based Genesis Genetics Institute, says that 70 percent of patients who are using PGD for gender selection wouldn't have needed in vitro fertilization in the first place.That means healthy, fertile couples are choosing this higher risk, expensive, sometimes painful process when they could conceive otherwise, Hughes said.Just like the controversy associated with embryonic stem cell research, there are concerns over what happens to the unused embryos created by PGD."It probably isn't an ethically good thing to do because you're creating embryos when you know you won't use half of them," said Winslow of the Florida Institute for Reproductive Medicine.Bioethicists say they also are concerned about the use of the technology as an instrument of gender discrimination."In China now, there are 117 boys for every 100 girls. In parts of northern India, it's 140 boys for every 100 girls," says Michael Sandel, a Harvard University professor and member of the President's Council on Bioethics.Bioethicists say they are concerned the preference of one sex over the other, in this case boys over girls, will create a future imbalance of population and power.Many European countries and Canada have banned sex selection in cases unrelated to any health purpose for some of the same concerns. The American Society of Reproductive Medicine has, in past statements, discouraged the use of PGD solely for sex selection.Most reproductive endocrinologists will not provide PGD unrelated to any medical purpose. It's only available at a small number of fertility clinics around the country.Despite the ethical concerns and the relatively limited availability, the use of PGD for sex selection continues to grow."We've just been handed a road map to the human genome, and what we're doing is taking a ride through the city learning about the terms and intricacies of where we want to go," said Steinberg of the Fertility Institutes, who waives concerns about sex discrimination, saying a little more than half of his clients request boys.Matthew and Beth Mandolesi said they are happy with their decision."At the time we did it, we didn't really think about the ethical part ...," Matthew said. "We've heard both sides since then. ... If we had to do it all over again, we would do it again."