Every pregnant woman gets asked the same questions. It seems like there is some unwritten list of the traditional inquiries everyone must make of an expectant mother, whether or not they are appropriate. One such inquiry is, “Do you want a boy or a girl?” Usually this is met by a glowing smile and the so-diplomatic, “I don’t care as long as it’s healthy!” When I was sitting in the waiting room of my doctor’s office the other day, however, I heard a response that definitely piqued my interest. A pregnant woman, who looked to be in her late thirties, responded to this question with, “I want a girl, which is why we only had sex at the beginning of my cycle. That guarantees I’m having a girl.” The other woman stared at her for a beat, nodded, and returned to her magazine. I was utterly fascinated. Is the timing of sex really applicable to the sex of the baby you conceived? Was it really possible to custom design your baby that way?

There has been extensive debate in the medical community over whether there is any truth to the ability of a couple to determine the sex of their baby by a range of means. Many old wives’ tales exist, claiming parents-to-be can do anything from change their sexual position to eating a particular meal prior to sex in order to influence the sex of their future baby. These, of course, have been almost exclusively debunked, but there are still theories that are honored by many practitioners. One such theory is the concept of determining birth by the timing of sexual intercourse.

Research has shown X chromosome spermatozoa and Y chromosome spermatozoa respond to the pH balance of a woman’s vagina and cervix differently. While highly acidic situations are damaging and demotivating to all sperm, it seems Y chromosome spermatozoa is far more sensitive to an acidic environment, but thrive in an alkaline environment. This has led some practitioners to recommend specific sexual timing for couples wanting to give themselves the best chances of having one sex or the other.

Studies in this area have shown couples who wish for a girl have the most success when they have sex two days prior to expected ovulation and then abstain entirely for up to a week after ovulation. This is when the vagina is primed for accepting sperm and delivering it to the cervix and uterus, where it can wait for several days for a released egg, but is also at its most acidic, and therefore least hospitable for Y chromosome spermatozoa. Couples hoping for a boy should wait until the day of ovulation in order to take advantage of the alkaline environment. Some may even wish to use lubricating jellies designed to either increase or decrease the acidity of the vagina, therefore boosting the chances of one sex or the other.

Source: Mori, Takahide. Ethical Considerations on Indications of Gender Selection in Japan, Journal of Assisted Reproduction and Genetics, September 2002, Volume 19, Issue 9, pp 420-425.