newborn in hospital

You may have heard that the odds of conceiving a boy or a girl is about 50-50. But have you ever wondered if it’s possible to influence the odds when it comes to the sex of your baby?

It may be — and there’s some science to back this idea. Some couples swear by what’s called the Shettles method. This method details when and how to have sexual intercourse in order to conceive either a boy or girl.

Let’s dive into this theory!

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The Shettles method has been around since the 1960s. It was developed by Landrum B. Shettles, a physician living in the United States.

Shettles studied sperm, the timing of intercourse, and other factors, like sexual position and the pH of body fluids, to determine what might have an effect on which sperm reach the egg first. After all, the sperm that fertilizes the egg is ultimately what determines the sex of the baby. (More on that process in a minute.)

From his research, Shettles developed a method that takes all these factors into account. As you can imagine, this information was in high demand. So, if you’d like some in-depth reading, you might consider picking up Shettles’ book “,” which was last updated and revised in 2006.

How sex is determined during conception

The sex of your baby is determined in the most basic way at the moment when the sperm meets the egg. A woman’s eggs are genetically coded with the female X chromosome. Men, on the other hand, produce millions of sperm during ejaculation. Roughly half of these sperm may be coded with the X chromosome while the other half carry the Y chromosome.

If the sperm that fertilizes the egg carries the Y chromosome, the resulting baby will likely inherit XY, which we associate with being a boy. If the sperm that fertilizes the egg carries the X chromosome, the resulting baby will likely inherit XX, meaning a girl.

Of course this depends on the most general understandings of and how it is defined.

Male vs. female sperm

Shettles studied sperm cells to observe their differences. What he theorized based on his observations is that Y (male) sperm are lighter, smaller, and have round heads. On the flip side, X (female) sperm are heavier, larger, and have oval-shaped heads.

Interestingly, he also studied sperm in some rare cases where men had fathered either mostly male or mostly female children. In the cases where the men had mostly male kids, Shettles discovered that the men had far more Y sperm than X sperm. And the opposite also rang true for the men who had mostly female kids.

Ideal boy/girl conditions

In addition to physical differences, Shettles believed that male sperm tend to swim more quickly in alkaline environments, like in the cervix and uterus. And female sperm tend to survive longer in the acidic conditions of the vaginal canal.

As a result, the actual method for conceiving a girl or boy via the Shettles method is dictated by timing and environmental conditions that help favor male or female sperm.

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According to Shettles, timing sex as close to or even after ovulation is the key to sway for a boy. Shettles explains that couples trying for a boy should avoid sex in the time between your menstrual period and days before ovulation. Instead, you should have sex on the very day of ovulation and up to 2 to 3 days after.

The method claims the ideal position for conceiving a boy is one that allows the sperm to be deposited as close to the cervix as possible. The position suggested by Shettles is with the woman being entered from behind, which allows for the deepest penetration.

Douching is another suggestion made by Shettles. Since the theory says that male sperm like a more alkaline environment, douching with 2 tablespoons of baking soda mixed with 1 quart of water may be effective. However, Shettles explains that douches need to be used before each timed intercourse.

Speak to your doctor before you try douching, as it’s generally by many doctors and the American College of Obstetricians and Gynecologists. Douching can change the balance of flora in the vagina and lead to infection. It may even lead to more serious health issues, like pelvic inflammatory disease, a complication of which is infertility.

Even the timing of orgasm is a consideration. With Shettles, couples are encouraged to have the woman orgasm first. Why does this matter? It all goes back to alkalinity.

Sperm are naturally more alkaline than the acidic environment of the vagina. So, if a woman orgasms first, the idea is that her secretions are more alkaline and may help the male sperm swim along to the egg.

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Swaying for a girl? The advice is basically the opposite.

To try for a girl, Shettles says to time sex earlier in the menstrual cycle and abstain in the days immediately before and after ovulation. This means that couples should have sex starting in the days after menstruation and then stop at least 3 days before ovulation.

According to Shettles, the best sexual position for conceiving a girl is one that allows for shallow penetration. This means missionary or face-to-face sex, which Shettles says will make the sperm have to travel farther in the acidic environment of the vagina, favoring the female sperm.

To add more acidity to the equation and favor the female sperm, Shettles suggests a douche made from 2 tablespoons of white vinegar and 1 quart of water can be used. Again, the douche should be used each time couples have sex to be the most effective. (And again, talk to your doctor before you give this specific douche a try.)

What about orgasm? To avoid adding more alkalinity to the environment, the method suggests a woman should try to refrain from orgasm until after the male has ejaculated.

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You can find plenty of people who will say that the method worked for them, but does the science support that?

Blogger Genevieve Howland at is one who says that the Shettles method helped her sway for a girl with her second pregnancy. She and her husband timed sex 3 days before ovulation and the pregnancy did result in a girl. She explains further that with her first pregnancy, they had sex right on the day of ovulation, which resulted in a boy.

This one case study aside, Shettles claims an overall 75 percent success rate in the current edition of his .

Not all researchers agree that things are so cut and dry, however.

In fact, a refutes Shettles’ claims. In those studies, researchers also took into account the timing of sexual intercourse, as well as markers of ovulation, like shift and peak .

The studies concluded that fewer male babies were conceived during the peak ovulation time. Instead, male babies tended to be conceived in “excess” 3 to 4 days before and in some cases 2 to 3 days after ovulation.

A more recent refutes the idea that X- and Y-containing sperm are shaped differently, which goes directly against Shettles’ research. And an older explains that sex 2 or 3 days after ovulation doesn’t necessarily lead to pregnancy at all.

The science is a bit murky here. Currently, the only guaranteed way to is through preimplantation genetic diagnosis (PGD), a test sometimes performed as part of in vitro fertilization (IVF) cycles.

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If you’re looking to get pregnant, experts recommend having sex every day to every other day, particularly around ovulation. Make an appointment with your doctor if your efforts don’t result in pregnancy after a year (sooner if you’re over age 35).

If you have your heart set on a girl or boy, trying the Shettles method won’t necessarily hurt — but it may make the process of getting pregnant take a bit longer. You’ll need to be in tune with when you ovulate and — most importantly — mentally prepared if your efforts do not end in your desired result.