The science behind sex selection

Can we choose the sex of our child?

Fertility specialists have the ability to create and identify embryos of either sex. But it's illegal to choose your baby's sex in Australia, unless there's a medical reason for it.

You can legally choose your baby's sex if you have a serious genetic condition that you risk passing on to your children (HFEA 2009a). Only pre-implantation genetic diagnosis (PGD) has been approved as a technique that does this.

So you can't medically intervene with conception just to balance your family, or for social or cultural reasons (HFEA 2009a, 2012).

There are some cheap, safe techniques that you can try in the privacy of your own home, although they're fairly unreliable. You could experiment with sex-selection kits or try folklore methods, such as eating more meat if you want a boy!

What would qualify us for sex selection?

You'll only qualify for pre-implantation genetic diagnosis (PGD) if you have a serious genetic disorder such as haemophilia or cystic fibrosis. PGD reduces the chance of your baby suffering from the same condition, partly by testing for the genes that carry it.

Your fertility specialist and a geneticist will decide if you qualify for PGD. In Australia, there's no national body that monitors these requests. Instead, controversial requests will be discussed by the ethics board of the medical group your doctor belongs to.

PGD is an in vitro fertilisation (IVF) technique. At the fertility clinic, embryos are created from your eggs and your partner's or donated sperm. After these are screened, a specialist will implant one embryo in your uterus (womb).

Sex as well as genes can play a part. Duchenne muscular dystrophy, for example, only affects boys. A disease such as haemophilia almost always passes from mum to son. In these circumstances, your doctor would just use a girl embryo. He wouldn't need to test for specific genes as well.

Your clinic will probably offer to freeze any spare embryos. You can then use these if you have a miscarriage, or if you'd like to have more children later on.

Some experts claim that the success rates for frozen embroyos are now almost equal to fresh transfers, with the added bonuses of reducing the need for more invasive testing and lower costs.

PGD, however, is expensive. Each IVF cycle costs an average of $4,000 after Medicare reimbursement, while PGD costs close to $4,000 more per cycle. Most fertility clinics can offer PGD.

What is sperm sorting?

Sperm sorting is when doctors try to separate male from female sperm. Sperm sorting is not available in Australia, but the service is offered, for a considerable fee, in some other countries (HFEA 2009c).

The most-used technique is flow cytometry, which is thought to be about 92 per cent accurate for girls, and 82 per cent for boys.

Flow cytometry works by adding a fluorescent dye to your partner's sperm sample. Experts can then tell male from female by seeing how the dye binds to the genetic material in the sperm.

Once sorted, you can then be implanted with the chosen sperm using relatively cheap intrauterine insemination (IUI).

There's no guarantee of success with sperm sorting. And IUI is not as effective as in vitro fertilisation (IVF).

Can timing intercourse decide my baby's sex?

There are two methods that claim to be able to achieve this: the Shettles method and the Whelan method, both named after the person that devised them. Bear in mind that these methods are theories rather than proven techniques.

You may decide to try one method if you understand your cycle well enough. But bear in mind that, whichever method you try, you always have a 50:50 chance of conceiving a baby of the sex you'd like.

The Shettles method
This is based on the idea that male sperm move faster, but don't live as long as female sperm.

So if you want a boy, you should aim to have sex as close as possible to ovulation (Shettles and Rorvik 2006), as the boy sperm will beat the girl sperm in the race to the egg. If you want a girl, you need to have sex two to four days before you ovulate.

Shettles claims that it's 75 per cent effective for girls and 80 per cent effective for boys (Shettles and Rorvik 2006).

The Whelan method
The Whelan method partly contradicts the Shettles method. It suggests that biochemical changes earlier in your cycle favour boy-producing sperm.

So if you want a boy, you should have sex four to six days before your basal body temperature goes up, or when your ovulation predictor kit (OPK) says you're about to ovulate. If you want a girl, you should have sex two to three days before you ovulate.

There may be more in this, as experts have found that male sperm have an advantage over female sperm at the very beginning and the end of your fertile window (James 2008, Jongbloet 2004). They also suggest that male sperm can survive longer than female sperm (van Dyk et al 2001).

Do sex-selection kits work?

DIY kits that claim to help with sex selection are based on the Shettles theory. Separate girl and boy kits can be ordered online and cost about $200. They generally include instructions, a basal thermometer, ovulation predictor test sticks, supplement tablets and douches that are supposedly sex-specific.

The US manufacturer claims a 96 per cent success rate, but many fertility experts say there's not enough evidence to support this claim.

Discover what the folklore says about choosing your baby's sex.