Sex position and baby's gender

 In the 1960s, physician Landrum B. Shettles studied sperm behavior and came up with a theory called the “Shettles method.” He then wrote a best-selling book called How to Choose the Sex of Your Baby. Shettles claimed both sex position and having sex at specific times during your cycle could influence the resulting baby’s gender.

Shettles based his theory on the belief that Y-chromosome-carrying sperm was lighter and swam faster than X-chromosome-carrying sperm, because the X chromosome is larger and contains more genes than the Y. And because X-bearing sperm is larger and “hardier,” he theorized, they were more able to survive acidic conditions, like the conditions of the vagina.

He wrote that having sex face-to-face (missionary position) with shallow penetration forces the sperm to travel farther in the acidic environment of the vagina, favoring sperm that would conceive a girl. Alternatively, to conceive a boy, Shettles wrote that having sex from behind, encouraging deep penetration, will deposit the sperm closer to the cervix, favoring male-producing sperm.

Shettles also claimed that which partner orgasmed, and in which order, could affect the baby’s gender. To conceive a girl, Shettles says the male partner should orgasm first, and vice versa if you are trying for a boy. Again this comes down to alkalinity, as Shettles believed female orgasm secretions were alkaline.

But is this true? Can certain positions really help you choose the sex of your baby? Probably not — or at least not reliably. Later studies, assisted by enhanced sperm analysis technology, found that Y-carrying sperm don’t swim faster, nor are they smaller or lighter than X-carrying sperm (multiple studies show no morphological differences between the two).

And further sperm studies found that the pH of the fluids to which sperm is exposed doesn’t seem to have a different effect on female-producing sperm, compared to male-producing sperm. In general, sperm is most motile in a neutral to slightly alkaline environment, between pH 7 and 8. The pH of the vagina is typically acidic, but shifts to neutral or alkaline just before ovulation, as a result of hormones that surge at that time. This helps facilitate fertilization.

The bottom line? There’s no robust evidence that sex position can influence your baby’s gender — so keep doing it in whatever way feels best for both of you. Learn more about sex while trying to conceive.