Whether you conceive a girl or a boy comes down to which sperm cell reaches the egg first. Every egg carries an X chromosome, while sperm carry either an X or a Y. When an X-bearing sperm fertilizes the egg, the result is an XX embryo: a girl. When a Y-bearing sperm wins the race, the result is XY: a boy. The father’s sperm determines the baby’s sex, and under normal circumstances, it’s roughly a 50/50 chance.
That said, couples have been trying to tip those odds for decades. The methods range from free, low-tech timing strategies to medical procedures that cost tens of thousands of dollars. Here’s what actually works, what probably doesn’t, and what the science says about each approach.
Timing-Based Methods
The most well-known natural approach is the Shettles method, based on the idea that X-bearing sperm (which produce girls) are slower but hardier than Y-bearing sperm, which are faster but die off sooner. Under this theory, having intercourse two to four days before ovulation gives the slower, longer-living X sperm a better chance of being the ones still around when the egg is released. Couples trying for a girl would avoid sex on the day of ovulation itself.
The Whelan method takes a similar but slightly different approach, recommending intercourse two to three days before ovulation. Women using this method track their basal body temperature each morning before getting out of bed, charting it across several cycles to pinpoint the day before a temperature spike, which signals ovulation.
Do These Methods Actually Work?
The evidence is genuinely mixed. The Shettles method originally claimed a 75% success rate for couples trying for girls and 80% for boys, based on data from the method’s creator. A 1979 study in The New England Journal of Medicine involving over 3,000 births supported the idea that intercourse timing affects fetal sex. But a 1991 study in The American Journal of Obstetrics and Gynecology produced the opposite result, finding fewer male births when conception happened during ovulation, which contradicts the Shettles model. Then a 1995 New England Journal of Medicine study refuted all timing claims entirely, finding no association between when couples had sex and whether they conceived a boy or girl.
Adding to the skepticism, research on sperm shape found no physical differences between X-bearing and Y-bearing sperm cells, undermining the core assumption behind the Shettles method. In short, timing your intercourse is free and harmless, but there’s no reliable evidence it shifts the odds in a meaningful way.
Sperm Sorting Techniques
A step up in complexity, sperm sorting attempts to separate X-bearing sperm from Y-bearing sperm before insemination. The Ericsson method works by placing a semen sample on top of a thick albumin protein solution in a glass column. Over about two and a half hours, sperm swim down through the liquid. Because Y-bearing sperm tend to move faster, they pass through first, leaving a higher concentration of X-bearing sperm behind. Those slower sperm are then collected and used for insemination.
A more advanced technology called MicroSort uses fluorescent dye and a laser to distinguish X sperm (which contain about 2.8% more DNA) from Y sperm. The Genetics and IVF Institute holds the licensing for this technology, and labs around the world use it. However, MicroSort remains under clinical trial oversight in the United States through an FDA investigational device exemption, which means access can be limited depending on your location.
Neither sperm sorting method guarantees results. They increase the proportion of X-bearing sperm in a sample, but some Y-bearing sperm remain. These methods are typically used alongside intrauterine insemination or IVF.
IVF With Genetic Testing
The only method that comes close to guaranteeing a girl is in vitro fertilization combined with preimplantation genetic testing. This is the same technology used to screen embryos for chromosomal abnormalities, and it reveals whether each embryo is XX (female) or XY (male). Your doctor then transfers only an embryo of the desired sex.
What the Process Looks Like
It starts with 10 to 14 days of injectable fertility medications to stimulate the ovaries to produce multiple eggs, with frequent ultrasound and blood work appointments during that window. Egg retrieval happens under sedation and takes about 20 to 30 minutes. The eggs are fertilized in a lab, and the resulting embryos grow in incubators for five to seven days until they reach the blastocyst stage.
At that point, a specialist removes a small cluster of cells from each embryo for genetic analysis. The lab examines the chromosomes to identify which embryos are XX and which are XY, while also screening for chromosomal abnormalities. Results take one to two weeks, so embryos are frozen during this period. Once results are back, you begin preparing for the transfer: estrogen builds the uterine lining over two to three weeks, with a few monitoring ultrasounds. The actual embryo transfer takes about five minutes.
Cost and Accuracy
The total cost for IVF with sex selection typically falls between $25,000 and $27,000, though it varies widely. Budget clinics may quote $11,000 to $12,000, while premium clinics can run $30,000 to $35,000 or more. The major cost components break down roughly as follows:
- Base IVF cycle: $9,000 to $25,000
- Genetic testing: $2,000 to $5,000
- Fertility medications: $3,000 to $7,000
- Frozen embryo transfer: $3,000 to $5,000
- Monitoring appointments: $500 to $2,000
Accuracy is very high. The American Society for Reproductive Medicine notes that diagnostic errors are rare, though not impossible. The bigger practical limitation is that you need at least one healthy embryo of the desired sex. If all your viable embryos happen to be XY, you’ll need to decide whether to transfer one anyway or do another cycle.
It’s worth noting that sex selection through IVF for non-medical reasons is considered controversial by medical ethics bodies. Some clinics won’t offer it unless there’s a medical justification, such as avoiding X-linked genetic conditions that primarily affect boys. Availability and willingness vary by clinic and by country.
Diet and Other Natural Claims
You’ll find advice online suggesting that a diet high in calcium and magnesium but low in sodium and potassium favors conceiving a girl. This idea has some basis in animal research. Studies in rats found that maternal diets high in sodium and potassium but low in calcium shifted the offspring sex ratio. Researchers have proposed that similar electrolyte effects could occur in humans, but the evidence in people is thin and far from conclusive.
Other popular suggestions include vaginal pH manipulation (the theory being that a more acidic environment favors X-bearing sperm) and specific sexual positions. None of these have strong scientific support. They persist largely because the 50/50 baseline means any method will appear to “work” about half the time, which is enough to generate convincing testimonials.
Realistic Expectations
Without medical intervention, your odds of having a girl are close to 50% no matter what you do. Natural timing and diet methods have not been reliably proven to shift those odds. Sperm sorting can nudge the probability higher but doesn’t guarantee an outcome. IVF with genetic testing is the only approach that lets you select with near-certainty, but it’s expensive, physically demanding, and not universally available for non-medical sex selection.
For most couples, the practical takeaway is straightforward: if you have a strong preference but aren’t willing to pursue IVF, the natural methods are harmless to try, just don’t count on them. If having a girl is a priority you’re willing to invest significant time and money in, genetic testing through IVF is the only method with the science to back it up.