A: There are a number of methods used by couples eager to choose the sex of their child. However, the financial, emotional and physical costs of these methods vary considerably.

The sex of your baby is determined by a sex chromosome that is carried in sperm. When a sperm carrying an X chromosome fertilizes an egg, a female offspring is conceived. When a sperm carries a Y chromosome, a male is conceived. The Y sperm contains slightly less genetic maternal than X-chromosome sperm. Y sperm are slightly lighter, travel faster and may be more fragile than X-chromosome sperm.

One method that some couples use to select the sex of a child is called the Shettles Method, which is based on the timing of intercourse. Because the Y-chromosome sperm swim faster, some people believe that timing sexual relations close to the time of ovulation may be more likely to produce a male child. Having sex two to four days before ovulation may increase the odds of having a girl. Though some doctors advocate this non-invasive technique, a study in the New England Journal of Medicine reported that there is no relationship between the timing of intercourse and the sex of a baby.

Other methods for sex selection rely on attempting to separate X and Y sperm prior to conception. These methods can increase the chances of conceiving a baby having the sex of your choice, but they are not fail-safe, require artificial insemination and may lead to disappointment a fair amount of the time.

The Ericcson Method uses a process of filtrating and centrifuging (spinning) sperm to encourage X and Y sperm sorting. The sperm are washed and separated in a laboratory at the time of ovulation, then placed by a doctor within the uterus using a small catheter. This is reported to be successful 70 percent of the time.

Another sperm separation technique uses a fluorescent dye to stain the sperm before sorting, and again places the sperm artificially within the uterus. Using this technique, researchers found that 65 percent of the cells sorted for boys had the Y chromosome, and 85 percent of the cells sorted to produce girls had the X chromosome.

An even more invasive and expensive method utilizes “preimplantation genetics.” Using in vitro fertilization techniques, doctors orchestrate the production of several embryos. This requires costly medication and invasive procedures. Each embryo can be then tested before implantation to determine its genetic sex. Only the embryos with the desired chromosomes will then be placed within the uterus. This technique is extremely involved and expensive, yet it is the most reliable.

You are your partner will need to decide how far you are willing to go to increase your chances of having a boy. With the exception of preimplantation genetics, these techniques are not fool-proof, and you should be prepared to embrace a child of either sex.