How to choose baby's sex

  • Lifestyle
  • Monday, 04 Oct 2010

Want a boy or a girl? Diet, when you have sex and what position you take are all factors.


It is illegal to use medical methods to choose the gender of your baby. In addition, it is unethical to choose the sex of your baby.

Nonetheless, a couple who has three girls and wants to try conceiving again would love to have a boy this time. And, vice versa for a couple who has all boys.

There are old wives' tales, pregnancy kits and even various methods that claim to help couples choose the sex of their baby. Just Google “gender selection” and you'll find various options.

What is the truth and which of these are just empty promises, lies and outrageous claims?

Obstetrician & gynaecologist and fertility specialist Dr Ng Kok Chong tries to clear the air on the issue.

He begins by asserting that gender selection is indeed unethical.

Dr Ng: 'We normally don't encourage it.'

“We normally don't encourage it but for those who already have three girls or three boys and want a baby of the opposite sex, then we can help advise them,” says Dr Ng.

Couples must firstly understand a few important facts about chromosomes and fertility.

Men have the XY sex chromosome while women have the XX sex chromosome. When the Y chromosome from the man mixes with the X chromosome from the woman, a baby boy is made. And, when the X chromosome from the man mixes with the X chromosome from the woman, a baby girl is made.

The Y chromosome is lighter than the X chromosome. The spermatozoa can carry either an X or a Y chromosome. Because the Y is lighter, the spermatozoa carrying it swims faster than other spermatozoa carrying the X chromosome.

Although lighter and faster, the Y chromosome is not as resistant as the X chromosome and spermatozoa carrying the Y chromosome tends to die faster.

Confused yet?

In simpler terms, there are male and female sperm. The male are faster and lighter than the female but tend to die faster. The female may be slow and heavier but they last longer.

When to have sex

Dr Ng advises those wanting to have a baby boy to have sexual intercourse after the wife ovulates. This is when the male sperm swim quickly to the egg, find it and fertilise it. X + Y = baby boy.

To have a baby girl, try having sex before ovulation. In such a situation, the male sperm may arrive first but they will find no egg and die waiting. By the time the egg emerges, the female sperm would have arrived in time to fertilise it. X + X = baby girl.

“To put it simply, your chances of getting a boy are higher if you have sex after ovulation and if you want a girl, your chances are better if you have sex before ovulation.

“It's not 100% accurate but your chances are better; possibly about 60% success rate,” explains Dr Ng.

Acidic and alkaline food

Your diet also matters. This is not an old wives' tale; there is a scientific explanation.

“The male sperm likes an alkaline environment while the female sperm likes an acidic environment. If the woman eats more fruits and vegetables the pH for the vagina is more alkaline. So the chances of getting a boy are higher.

“If you want a boy then the man needs to take more acidic food like meat while the woman needs to take more alkaline food like vegetables and fruits.

“If you want a girl, then the woman needs to eat more meat and the husband needs to take more vegetables. Then the environment of the vagina is more acidic and the chances of getting a girl are higher,” explains Dr Ng.

Again, he reminds couples that the success rate is only about 60%.

Take your position

Another element to help in gender selection is the sex position. Positions that offer deep penetration make it easier for the sperm to get to the egg quickly and, because of that, the chances of getting a boy are higher.

However, if there is shallow penetration, then the sperm need to swim farther and by the time they get to the egg, the male sperm would have died. So, the chances of getting a girl are higher.

Medical methods

There are also medical methods to get a boy or girl but these are only done if the family members are afflicted with serious genetic conditions, such as haemophilia or Down Syndrome.

In such cases, the male and female sperm can be separated during an IUI (intra-uterine insemination) procedure.

One method is called the swim up method where we put the semen in a test tube with some chemicals. The sperm will swim up the tube and the male sperm swims faster so it will be at the top of the test tube. Then we will remove the sperm at the top of the test tube, wash it and inject it into the wife's womb. So the chances of getting a boy are higher.

The IUI method for gender selection can only be done to have boys. You can't take the sperm from the bottom of the test tube because the sperm there is not as active and the chances of getting pregnant from that are not very high.

The final method is via PGD (preimplantation genetic diagnosis). This is done in concert with IVF (in vitro fertilisation) treatment where the woman's eggs are removed after ovarian stimulation for fertilisation with the man's sperm outside the body.

“The fertilised eggs are nurtured in an incubator until they go through a process called cell division, which is when they become embryos.

What we do is that once the embryo reaches the eight cell stage, we remove one cell and do a chromosome study on it.

“The embryos that are healthy and which contain the genetic characteristics that are desired by the couple are then transferred into the woman's uterus,” says Dr Ng.

According to him the PGD method is almost 99.9% accurate.

These two methods can only be conducted for medical reasons.


* Having sex more often gives you a girl and less often gives you a boy. - Not true, says Dr Ng.

* Chinese birth gender chart. – Dr Ng says he doesn't think this is accurate.

* One-year chart of when to have intercourse to get a boy or girl. - Dr Ng says it is highly unlikely that a chart for one year can be accurate. “How can it be accurate when your ovulation dates depend on when you have your period and how long each cycle is? It's very difficult to be accurate when giving dates for a whole year,” he says.

* The wife douches with sodium bicarbonate and water to get a boy. - Dr Ng says this may not be safe or clean. “Some people believe that douching with sodium bicarbonate to wash their vagina before sex creates a more alkaline environment. They do this if they want to have a baby boy. We don't advise douching as a means to clean the vagina, so this is definitely not recommended anyway.”

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