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Expert Q&A

	By Craig Sweet, M.D. Reproductive Endocrinologist

I have three boys already. Is there anything that I can do to increase my chance of having a girl? I have heard wife's tales, but I was wondering if there is anything more scientific available.

In general, the chances of having a girl as the fourth child after having had three boys is only about 44 percent. Call it unfair, but those are the odds. The following website provides detailed information on the topic:

http://www.in-gender.com/XYU/Odds/Gender_Odds.aspx

Couples have been trying to select the sex of their children for thousands of years. In the past, it was thought:

• Males developed on the right side of the uterus and females on the left. (5th Century B.C.)
• An orgasm by the woman before the man selected for male offspring. (Talmud, Leviticus 12:2)
• The child's sex was the same as the sex of the most active partner during the procreative process! (Aristotle) [This explanation is my personal favorite!]
• Copulation with the heads of the couples pointed north favored the birth of a male child.

In the more recent past, the selection of the child's sex was supposedly accomplished by manipulating the timing and intercourse techniques. It was thought that the Y-bearing sperm (male) were smaller, more streamlined and a bit quicker. By withdrawing slightly at ejaculation making the overall distance greater, the streamlined Y-bearing sperm would cross the finish line first. Too bad it didn't work.

Any reproductive facility that touts the use of routine sperm washing techniques as a bona fide method of sex selection should be questioned carefully. It should also be remembered that about 51 percent of all births in the US are male, so a very small natural shift for uncertain reasons towards a male delivery is generally seen.

Two techniques actually work. One is called Microsort. This process separates the X- and Y-bearing sperm, although it is a bit better at selecting out the X-bearing (female) sperm. When sorting for the X-bearing sperm to produce a girl, 88 percent of the sperm will be carrying the X chromosome. The technique is not quite so accurate for the Y-bearing sperm (73 percent) since the Y chromosome is so much smaller than the X, and it doesn't "light up" as well during the separation process. My facility has been part of this FDA-approved study for a number of years. Additional information may be found on the following web sites:

• http://www.microsort.net/
• http://www.dreamababy.com/sex-selection.htm
• http://www.dreamababy.com/microsort-process.htm

In reality, however, the process of pre-implantation genetic screening (PGS) is even more accurate, hovering around the 95 to 98-percent rate. In this technique, eggs are removed and fertilized by the partner's sperm, creating embryos via in vitro fertilization (IVF). The embryos are grown to the third day wherein a single cell is carefully removed from the seven- or eight-cell-stage embryo and sent for genetic analysis. Not only is the single cell screened for excess chromosomes (i.e., Down syndrome) and missing chromosomes (Turner syndrome), the embryos are also screened for gender. While not perfect, the accuracy is really quite amazing. In general, only one or two of the gender-preferred embryos are then transferred on the fifth or six day of growth. This technique is the most expensive of the options, but yields the highest and most accurate success rates in the shortest period of time. While rare, one must be prepared that none of the embryos will be of the desired gender. In our practice, we have asked that the embryos not "gender desired" be donated or used for stem cell research but that they not be destroyed.

A friendly visit to your neighborhood reproductive endocrinologist is in order to get additional details, and don't be shy about the costs as well as as the success and failure rates of any procedure being considered.

Good luck!

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