The likelihood of conceiving either a boy or a girl is roughly even.
But, to be accurate, the World Health Organisation puts it slightly in favour of male births (105 males born per every 100 females).
However, is there any way to swing the chances in favour of either sex?
The Shettles Method
Dr Shettles, a US physician in the 1960s, believed it was possible to influence the sex of a baby at conception. He studied sperm and drew conclusions about the differences in sperm that produced males versus the sperm that produced females.
He based his advice on his own research and suggested sexual positions to ensure the desired gender of the baby. For example, he advised couples who wanted a son to opt for a “doggy-style” position.
Solving X and Y
There is very little evidence supporting the Shettles Method, but what we know to be true is that sperm determines the sex of a baby.
A woman’s eggs are genetically coded with only the female X chromosome. Whereas roughly half of a male’s sperm has an X chromosome and the other half a Y. Upon fertilization of an egg and a sperm, an XY union will produce a boy and an XX, a baby girl.
What do the scientists believe is the best position?
Luckily, the smartest scientists are not spending their time advising who should be on top. Rather, they are positioning themselves in a much more exciting space.
The latest research has discovered that Y- and X-bearing sperm have relatively different characteristics i.e., they have a slightly different shape, size, motility pattern and electrical charge to each other.
Scientists can now take a sperm sample and spin it at exactly the right speed in a centrifuge, which separates the two sperm types along the depth of a tube. The X-bearing sperm are ever so slightly denser and will settle at the bottom of the tube.
Whereas the lighter Y’s will float on top. Then, using a pipette, scientists can carefully, with almost perfect precision, select the desired fraction of the tube – either at the top to collect male-producing sperm, or at the bottom, for female-producing sperm.