The question is asked of almost every prospective parent: "Would you prefer a girl or a boy?"
Now, doctors at Houston's Baylor College of Medicine are conducting a "sex selection" study that will allow couples to make that wish come true -- letting them actually pick their baby's gender.
"We want to know whether using this technology for elective non-medical reasons is a good idea," said Dr. Sandra Carson, director of Baylor's Assisted Reproductive Technology program.
Doctors often analyze embryos for genetic defects, some of which are more common in boys or girls. But in the Baylor study, up to 200 couples going through in vitro fertilization will be allowed to pick either male or female embryos, so researchers can better understand their motivation.
"Before we make the procedure available in a routine, clinical way, I think it's a good idea to get actual facts from couples who are actually doing it," said Carson.
Couples must answer detailed questions about why they want a boy or a girl and how their expectations may differ between having a son or daughter.
The whole idea of picking a baby's sex is so controversial, it took nine years for researchers to get permission to conduct the study.
The practice, known as "social sex selection," is banned in many countries, including Britain and Canada. It is opposed by major medical organizations in the United States.
"Once you say it's OK to screen for gender, there's nothing that you can say that it's not OK to screen for -- whether it's eye color, hair color, trivial issues," said Boston University ethicist and legal scholar George Annas.
But one recent survey conducted by the University of Illinois at Chicago found 59 percent of women would not use sex selection even if it were free.
"I would never opt for this procedure," one woman told ABC News. "I think it's [childbirth] one of the world's greatest surprises."
According to many ethicists, that's the way it should stay.
ABC News' John McKenzie filed this report for "World News Tonight."