The idea of pushing a blue or pink button and popping out a baby of choice is way off the mark. The biotechnology dictating how nature takes its course is much more complex, amazing, and flawed. Here's a look at what science has developed so far.
Preimplantation Genetic Diagnosis
WHAT IT IS: A technique that uses fluorescent color to identify the male and female chromosomes on embryonic cells.
HOW IT WORKS: Charles Strom, M.D., Ph.D., director of medical genetics at Illinois Masonic Medical Center, in Chicago, explains the procedure: "The woman takes a medication that causes her to make multiple eggs, which are then suctioned by needle from her ovaries. The eggs are placed on tissue culture plates, where they are fertilized with sperm -- usually the husband's -- a routine procedure for in vitro fertilization. Then the embryos are grown in a test tube until they have multiplied to five to ten cells, which takes about two days. A single cell from each embryo is analyzed, using a technique that attaches fluorescent probes to specific DNA sequences. If it's a male, you have one green strand and one red strand of DNA; if it's a female, both strands are green." Once the sex has been determined, the doctor implants two or three embryos of the chosen gender into the woman's uterus.
SUCCESS RATE: Determining the sex through this procedure is close to 100 percent reliable. There is no guarantee, however, that implantation will work.
WHO IS ELIGIBLE: This method is only available to couples who have a hereditary disease in the family.
COST: $10,000 for in vitro fertilization plus $2,500 for preimplantation diagnosis per menstrual cycle (it can take at least two or three menstrual cycles for a woman to conceive).
RESOURCES: There are approximately 30 centers in the world -- about a fifth of which are in the United States. Go to www.genetests.org.
Flow Cytometric Separation
WHAT IT IS: A sperm-sorting technique, also known as MicroSort, practiced at the Genetics & IVF Institute, in Fairfax, VA.
HOW IT WORKS: Prospective parents submit a sperm sample to doctors at the clinic, who stain the sperm with a fluorescent dye. Individual sperm carry either X or Y chromosomes; since X (which determine that the baby will be a girl) have slightly more DNA than Y (which determine that the child will be male), they absorb more dye. After a machine sorts the sperm, doctors perform intrauterine insemination (injecting the desired sperm into the uterus through the cervix).
One concern among doctors wary of this technique: Though the dye used to stain the DNA is considered nontoxic, its long-term effects are still unknown.
SUCCESS RATE: This method is still considered an experimental procedure, but statistics from the ongoing clinical trial at the Genetics & IVF Institute show promise. "Ninety percent of the girls and seventy percent of the boys born are the sex their parents desired," says Susan Black, M.D., a medical geneticist at the Institute.
WHO IS ELIGIBLE: Married couples with at least one child who are interested in "balancing" their families. For families with a hereditary disease, however, the child requirement is waived. The Institute does a phone interview and asks participants to have screening tests done at a lab near their home. The procedure takes place in Virginia at the Institute. There is a waiting list of several months.
COST: $3,200 per menstrual cycle (it can take at least three tries on average).
RESOURCES: The Genetics & IVF Institute, in Fairfax, VA. Call or go to www.microsort.net.
Albumin Filtration Method
WHAT IT IS: Developed by Ronald Ericsson, Ph.D., and popularly known as the Ericsson Method, this technique, separates X- and Y-bearing sperm by spinning them in a centrifuge.
HOW IT WORKS: The lighter Y-bearing sperm rise to the top and the heavier X-sperm sink. Once the sperm are isolated and collected according to the desired sex, they are inserted by intrauterine insemination. If the couple is trying for a girl, Ericsson also recommends that the woman take the fertility drug clomiphene citrate, which is generally taken to increase the production of eggs. Although he can't explain the correlation, Ericsson notes that in his experience the drug has seemed to increase the chances of couples conceiving girls.
SUCCESS RATE: According to studies published by Ericsson, the albumin filtration method has a success rate of more than 80 percent for parents wanting boys and 73 percent for those wanting girls, figures that he says have been confirmed in more than 40 clinics worldwide that use his technique. Other doctors of reproductive medicine, however, say that other scientists have been unable to reproduce Ericsson's results.
WHO IS ELIGIBLE: Anyone who can afford it.
COST: $500 to $1,000 per menstrual cycle (it can take at least two or three menstrual cycles to conceive).
RESOURCES: Ericsson's website, www.childselect.com, lists all clinics licensed to perform his patented technique.
WHAT IT IS: Named after Landrum Shettles, M.D., Ph.D., a former associate professor of obstetrics and gynecology at Columbia University, this method proposes that the timing of intercourse and the use of specific positions can help determine a baby's sex.
HOW IT WORKS: Noting that the X-bearing (female) sperm are hardier and slower moving than Y (male) sperm, Dr. Shettles advises couples wanting a girl to have sex two or more days before ovulation. When the egg finally arrives, Dr. Shettles believes that there's a better chance that only the female sperm will remain to fertilize it. Other directives for conceiving a girl include using the missionary position, which deposits sperm farther from the cervix, thereby making the robust female sperm the odds-on favorite for surviving the longer trip. He also suggests that the woman avoid having an orgasm, as it increases the alkaline secretions that he says tend to favor male sperm.
Conversely, to have a boy, Dr. Shettles says that intercourse should occur as close to ovulation as possible to give the male sperm a fighting chance. He also maintains that the rear entry position is preferable because the sperm would be deposited closer to the cervix. And, in this case, he advises that the woman climax.
SUCCESS RATE: Many doctors claim there is no scientific basis for these techniques. "Methods for sex selection such as timing of intercourse, using certain positions, adopting a certain diet, and the like are quackery," says Dr. Stillman. But Dr. Shettles and David Rorvik, his coauthor of How to Choose the Sex of Your Baby, claim that readers who follow their advice have at least a 75 percent chance of conceiving the child of their choice.
COST: $13 -- the price of the book.
WHO IS ELIGIBLE: Anyone willing to follow the procedures.
RESOURCES: The book.
WHAT IT IS: This sex-selection technique, named after author Elizabeth Whelan, is centered around the timing of intercourse.
HOW IT WORKS: Unlike Dr. Shettles, Whelan claims that the best way to increase the odds of having a boy is to have sex four to six days before you ovulate and for a girl, to abstain from intercourse until two or three days before ovulation. Her advice is based in part on studies done by Rodrigo Guerrero V., M.D., a physician studying at the Harvard School of Public Health in the late 1960s, who charted outcomes of couples who timed their conceptions.
SUCCESS RATE: Whelan claims her success rate is 68 percent for boys and 58 percent for girls. Like Dr. Shettles' method, Whelan's isn't universally accepted by doctors of reproductive medicine.
COST: $5.99 -- the price of her book, Boy or Girl?
WHO IS ELIGIBLE: Any woman with a calendar, a thermometer to pinpoint ovulation, and a regular menstrual cycle.
RESOURCES: The book.