Last night Chrissy Teigen made her family plans very clear: After undergoing in vitro fertilization (IVF) treatment and giving birth to a girl last April, she's now ready for a boy. "Oh my God, a little boy is next for sure!" she said in an interview at the Screen Actors Guild Awards. During her previous pregnancy, Teigen said that she specifically chose a female embryo with the hopes that it would foster a special father-daughter bond with her husband, John Legend. This time around, though, she hasn't specifically said she'd like to pick the sex of her next child — it's just that the embryo they have left is male. (And she isn't pregnant yet, to be clear.) So how does that whole sex-selection process actually work? The basis of any IVF procedure is that eggs are fertilized with sperm outside of the uterus. Then, once the embryos begin to develop, they are transferred into the patient's uterus. Traditionally, your doctor would take a look at cells from the embryos to decide which ones have the best chance of creating a successful pregnancy before they're implanted. But now, with the addition of an extra screening step that has become more and more popular in the last few decades, he or she can also look at a variety of other factors. That includes examining the chromosomes for any potential health issues. And during that additional screening, the sex of each embryo is revealed (XX or XY). “If more than one embryo is normal, and there happen to be both males and females, we don’t impose on patients which one they should use,” Avner Hershlag, MD, chief of the Center for Human Reproduction at North Shore University Hospital told Health. “If all other things are equal, it becomes their personal choice.” However, this kind of screening poses both a financial and ethical dilemma for some. For one thing, that extra step does not come cheap — clinics often charge around $4,000 to add PGD or PGS screening to the overall IVF total. Then there are concerns among some bioethics experts that the procedure may actually hurt the embryo or be subject to a gender bias. But other experts don't believe that there's anything unethical or dangerous about the procedure, despite the controversy it tends to bring. Teigen faced a fair amount of criticism for saying she explicitly chose a female embryo last year. But, you know, we're in favor of people making decisions about what goes on in their own uteruses.