Misconception: Can you influence the sex of your baby?

Home » Rebecca Reilly » Misconception: Can you influence the sex of your baby?

7 March 2022

Reading Time: 3 minutes

If you’re about to try out an old wives’ tale, make sure to do your reading.

Wear your boots to bed. Have sex while facing your right side, or from behind. Eat lots of meat. All of these things have been proposed as ways of ensuring you have a baby boy. Want a girl? Try eating lots of chocolate, or pinching your partner’s right testicle while you’re doing the deed. Aristotle advised those wanting a boy to have intercourse when the wind is in the north.

There are tons of myths, stories, old wives’ tales and theories out there around fertility and conception. You might have heard (or experienced) people claiming to be able to tell the sex of your baby from the way you’re “carrying” when pregnant, for example.

Fertility is an area – much like nutrition, which I’ve talked about before – where there’s no shortage of unscrupulous marketers ready to part vulnerable people from their cash based on science-ish sounding theories and unproven claims. Sex selection – being able to predetermine the sex of your baby – is (pardon the pun) fertile territory for this.

Some of us might quite like to be able to “balance” our families by having a girl or a boy, depending on our other children. Or sometimes there’s the less savoury, but still existing, patriarchal pressure to produce a boy. All of this has given rise to an industry profiting from it. But, very few theories are backed by evidence.

To be clear: it’s possible to pretty accurately discern and ensure a male or female embryo via certain practices around IVF. There’s technological ways to separate out male and female sperm precisely, with a high success rate in the ensuing pregnancies producing babies of the desired sex. However, this – and any other procedure aimed at selecting an embryo based on sex – is illegal in New Zealand. The only exception is when parents are at high risk of gender-specific genetic disorders.

A still-popular theory to get your preferred sex is the Shettles Method, devised by the doctor of the same name in the 1970s. He proposed that having sex as close to the moment of ovulation as possible would increase the likelihood of having a boy. This was based on his determination that a Y-carrying sperm would swim faster and get to the egg first, due to it being a different shape to the female, X-carrying sperm. Shettles reckoned X-carrying sperm were more robust, and survived longer, so if you wanted a girl, you should have sex a few days earlier, with shallow penetration.

While this sounds plausible – and Shettles himself claimed evidence to support it – the Shettles Method has now been debunked by further study. By 2006, researchers could see there was not actually any difference in shape between X sperm and Y sperm, and there was no evidence of Y sperm being faster swimmers.

Other theories around eating certain foods, including increasing potassium, calcium and/or magnesium in the diet producing more girls, and a higher calorie diet favouring boys, don’t have solid evidence behind them, either. A 2018 review looking at maternal nutrition and its effect on sex concluded there hasn’t been enough research on the topic; the few studies have found many different and fairly underwhelming results.

So with this in mind, all we do know is there’s a 50 percent chance of having a baby of your preferred sex (if you even have a preference). But, there is a lot you can do to increase the chances of a healthy baby. That includes both you and your partner focusing on the big four: diet, exercise, sleep and stress. If you get all of those into the best possible shape before trying to get pregnant, there should be no weird positions or checking of the wind direction necessary.

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