Can You Increase Your Odds Of Conceiving A Girl?
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If you're trying to get pregnant and want to conceive a girl, there's a lot of sketchy advice out there — like suggestions that you eat more oranges, have sex in front of a space heater, or make sure you don't have an orgasm (great). But is there actually a scientifically sound way for parents-to-be to pick their baby's sex?

"Mother Nature has already tipped the scale a little in favor of boys," gynecologist Dr. Renee Allen tells Bustle. "According to data from the National Center for Health Statistics, approximately 105 boys are born for every 100 girls." However, she says, many people choose to manipulate the odds, through both scientifically proven and slightly more questionable means.

Whatever future parents are trying today, they're in a better positions than past generations. Today, we know how a fetus's sex is determined (all eggs carry only an X chromosome; sex is determined by whether the sperm that fertilizes it contains another X chromosome, which would make the fetus female, or a Y, which would make it male). But in that past, it was all guesswork. Medieval physicians were convinced that the right testicle produced boys and the left produced girls, which led to some interesting arrangements. For example, compensation for having your left testicle removed by accident in medieval Ireland was much lower than for the right one, because people were so focused on producing male heirs. Other lore held that you could ensure a male fetus by having sex facing the east, eating the heel of a loaf of bread, and dropping breast milk into water, but it was obviously all based on myth instead of fact.

As science marches forward, we've become more astute at understanding what happens when we get knocked up, and what kind of influence we can exert in the process.  There is, of course, the question of whether it's ethical to pick your child's sex, or to invest this much energy in the sex your child is assigned at birth, since this may not end up matching their gender. But if you're curious about the pure science, here's what we now know about increasing the odds that you'll conceive a girl.

Age, Stress, And Family History Can Be Factors

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The lives of parents-to-be seem to have a surprisingly direct impact on the sex of their kids. For instance, it was suggested in a 2011 study that the amount of stress the mother is under could influence the sex of her child; if she worked a high-stress job, the statistics indicated, she was more likely to have a girl.

Age is another factor: the odds of conceiving a girl increase slightly as the mother or the father age. Parents who have already given birth to other children also experience increased odds of becoming pregnant with a girl. (Though the impact of both of these factors are small.)

And some of it might be in your genes. A 2008 study, for instance, revealed that men inherit genetic tendencies to have a certain predominance in their sperm; if they come from a family with many girls, they're more likely to produce female children themselves.

Your Eating Habits & Chemical Exposure Could Play A Role, Too

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Though many myths hold that a baby's sex can be determined through eating certain food, one study showed that food can play a role in determining a baby's sex — just not in the way you might think. A study by Exeter University in 2008 found a distinct link between nutrition and the sex of fetuses: mothers who ate a high number of calories per day before and in the early stages of their pregnancy had a 56 percent chance of conceiving a son, while mothers who ate a lower calorie diet only had a 46 percent chance. The lead author, Dr. Fiona Matthews, explained at the time that "If a mother has plentiful resources then it can make sense to invest in producing a son because he is likely to produce more grandchildren than would a daughter. However, in leaner times, having a daughter is a safer bet.”

This may be the force behind something that puzzled scientists for quite a long time: why the male-female birth ratio in industrialized, wealthy countries from Denmark to Canada has been skewing slightly towards females for decades. Technically speaking, the healthier diets and better socioeconomic circumstances should mean more males,  but Matthews and her fellow scientists wonder if perhaps low-carb diets and the emphasis on low body weight among women in Western culture may mean they have more daughters. None of this is to say that cutting down your calorie intake in pursuit of a female fetus is a good idea — it's recommended that pregnant women increase their caloric intake for health reasons.

And, in less appealing options, exposure to environmental toxins may also play a role. Dioxin, a toxic chemical that is an industrial by-product and was once present in many herbicides, has been found to influence sex. Men who worked jobs that caused them to come in contact with herbicides containing dioxin have been shown to be less likely to father male children, as are guys who have had contact with a compound called 1,2-dibromo-3-chloropropane (DBCP) that kills worms. And exposure to contaminated rice that had dioxin-like properties in it had the same impact on male workers in Taiwan.

The Time Of The Month That You Have Sex Could Influence Things

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The idea that sperm of different chromosomal make-ups swim at different speeds is disputed, but it's also the foundation of one of the most famous (and scientifically questioned) baby-selecting methods, the Shettles Method. This method recommends that couples wanting a boy should have sex close to the moment of ovulation, because Y sperm supposedly swim faster, while those wanting a girl should wait 2-3 days before ovulation to allow the allegedly slower X sperm to meet up with the egg.

However, a letter published in the British Medical Journal in 2006 explains that "so far, researchers have found no morphological differences between human X sperm and Y sperm. Neither mature sperm nor their precursors possess significant morphological differences between X and Y genotype; and Y bull sperm do not swim faster than X sperm."

So attempting to strike at the right moment might not have any effect whatsoever. Dr. Allen says that "many fertility experts question the value of natural sex selection strategies such as the Shettles method. The main consensus is that Shettles' ideas seem to make sense, but they're a little too simplistic and not based on scientific research to be taken seriously. Nonetheless, the Shettles method has reportedly been effective at least 75 percent of the time, with the rate slightly lower for girls than for boys."

But If You Want To Bee 100 Percent Sure, Head To A Lab

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Of course, if you absolutely want to ensure that your child is born a specific sex, there are scientific methods that will yield results — but they're often expensive and invasive. One method is called Preimplantation Genetic Diagnosis, or PGD; it was in the news recently because it was revealed that Chrissy Teigen and husband John Legend had used it to select a female embryo, created via IVF, to have their baby Luna after nine years of attempting a natural pregnancy.

PGD isn't designed purely for gender selection. It's actually a genetic screening process created to scan embryos created via IVF for inherited genetic conditions; discovering the embryos' genders comes as a welcome additional piece of information. Dr. Allen explains that it works by examining an embryo's chromosomes:

Once the tests are done, the embryos can then be chosen and implanted in the mother to become (hopefully) a viable, full-term pregnancy, and the rest frozen — which is why Teigen and Legend know that their next child will be a boy, as that's the gender of the remaining frozen embryo. The process is strongly successful — Dr. Allen predicts a 97 to 99.9 percent accuracy rate — but also expensive. "A single round of IVF with preimplantation genetic testing can cost more than $20,000," Allen says. "Specifically, the average cost of a single IVF cycle is $12,400, according to the American Society for Reproductive Medicine.  Preimplantation genetic testing adds another $5,000 to $8,000 to the tab."

There's another method of attempting to get involved in the fertilization process before embryos are even formed: discovering which sperm are X-sperm or Y-sperm, separating them off, and using the desired sperm for fertilizing the egg. (Obviously this can only be done in a lab, not at home with a sperm sample and a turkey baster.)

"These methods work on the premise that they separate the X and Y-sperm by use of centrifugation," Dr. Allen explains. "During centrifugation, controlled spinning causes particles in a sample to become sorted into layers according to density of those particles. Sorting separates the more dense X-sperm from the lighter Y-sperm."

But again, this kind of reliable sex selection doesn't come cheaply. "Sperm sorting is 78 to 85 percent effective when it comes to choosing boys and 73 to 75 percent effective for selecting girls," Dr. Allen says, but estimated the price at $600 to $2500 per cycle.

What Absolutely Doesn't Help You Conceive A Girl?

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But while whats does work is often still up for discussion, we do know what doesn't work.

One myth Dr. Allen wants to debunk is that sexual position influences conception. "The rear-entry position or having intercourse standing up is supposedly best for couples wanting a boy because it deposits the male sperm closer to the egg and farther away from the vagina's acidic environment," she notes, but the science of the method doesn't check out. Other old wives' tales include making sure women orgasm if they want to have a boy, because "it is thought that the contractions that accompany an orgasm also help move the male sperm into the cervix," a theory which has no factual basis. Another myth holds the baby will have the sex of the person who climaxes first. "I hypothesize that if this ridiculous theory was factual," she adds, "the world’s population would be 98 percent male!"

Other theories that sound more scientific are also, she points out, completely without basis. Moon monitoring (full moon for a girl, quarter moon for a boy), diets (potassium-rich diets for a boy, magnesium-high ones for a girl), and douching with either vinegar or baking soda to affect the vagina's pH are also out. "You will be hard-pressed to find an OBGYN in this day and age who recommends routine douching," she notes, "since this practice can change the natural bacterial environment of the vagina, which can lead to more vaginal infections."

So in the end, there's no truly reliable way to ensure your baby's sex without shelling out a lot of money and time to your local IVF lab. But, if you want to go on tons of Tinder dates with men who have lots of aunts, or have tons of sex right before you ovulate, well, go for it. Even if doesn't help you conceive a girl, it still sounds pretty fun.