Guide
How to conceive a girl or a boy: what the evidence says
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There is no proven natural way to choose whether you conceive a girl or a boy. The most widely followed approach is the Shettles method: intercourse two to four days before ovulation when hoping for a girl, and as close to ovulation as possible when hoping for a boy. Research has not consistently supported it, so treat it as a plan to follow, not a promise.
The honest starting point
Slightly more boys than girls are born worldwide, roughly 105 boys for every 100 girls. The sex of a baby is decided by whether the sperm that fertilises the egg carries an X or a Y chromosome, and no natural method has been shown to reliably change that.
The two routes at a glance
| Hoping for a girl (XX) | Hoping for a boy (XY) | |
|---|---|---|
| Shettles timing | Intercourse 2–4 days before ovulation | Intercourse as close to ovulation as possible |
| Vaginal environment (theory) | More acidic | More alkaline |
| Reasoning in the theory | X-bearing sperm are said to survive longer | Y-bearing sperm are said to swim faster |
| Genesyx programme | XX programme | XY programme |
Timing
Every timing-based method depends on knowing when you ovulate. Our guide to ovulation tests and your fertile window explains how to find it. Timing intercourse away from ovulation, as the girl route suggests, may make conception take longer.
Vaginal pH
The Shettles theory proposes that vaginal pH may affect X- and Y-bearing sperm differently. Genesyx includes at-home vaginal pH tests so you have readings rather than guesses. Never douche or use home remedies to change your pH; they can cause irritation and infection.
Diet
Some small studies have linked diet around conception with a baby’s sex, but the findings have not been reliably replicated.
What the research says
A widely cited 1995 study in the New England Journal of Medicine found no link between the timing of intercourse relative to ovulation and the sex of the baby. More on our evidence page.
Things to keep in mind
- If you have been trying to conceive for over a year (or six months if you are over 35), speak to your GP.
- In the UK, choosing a baby’s sex through IVF for non-medical reasons is not permitted.
Evidence for the Shettles theory is mixed. Genesyx helps you follow the theory consistently; no outcome is guaranteed. This page is general information, not medical advice.