In the 1960s, an idea started to form and made very popular by Dr Shettles and Rorvik in their book How to Choose The Sex Of Your Baby.
In this book, Dr Shettles claimed to have noticed that there were two distinct populations of spermatozoa and concluded that the ones with the smaller heads had the Y chromosomes, while the ones with the bigger heads contained the X chromosomes.
The following year, he reported that the ones with the smaller heads could move more rapidly that the bigger heads and invariably fertilize the eggs in the fallopian tube more often.
Immediately after this research, people started to believe that the Y sperms swim faster than the X sperms and began to research on sperm separation.
So, what did they find?
- There were no differences in the appearances of the X and Y sperms
- Y sperms do not swim faster than X sperms
What do these things mean?
Here are a few things to note:
- A chromosome is simply a piece of genetic material, it contains genetic information
- The woman’s eggs contain the X chromosome
- The sperms contain either the Y or the X chromosome
- To make a boy, you need X egg to meet the Y chromosome
- To make a girl, you need X egg to meet the X chromosome
During ejaculation, between 40-150 million sperms are released into the vagina. Some carrying the X, others carrying the Y, swimming to the egg in the fallopian tubes of the woman.
Out of the millions that are released, only a few hundred comes close to the egg, the rest are lost along the way, some are killed by the immune system of the woman, others die when their energy sources become worn out.
The egg makes it way from the ovaries: what is called the egg bank and makes its way to the fallopian tubes, they know that they have to meet halfway if they want to get fertilized.
Remember the egg only has only the X chromosome waiting for whatever sperm is coming around, usually the first to get to the egg. Now the sperms are racing to meet it!
The idea behind this is, if you have sex close to your ovulation, you are more likely to give birth to a boy because your Y sperms are faster and die faster, while if you have sex away from the ovulation, the X sperms that live longer will be the ones to fertilize leading to a baby girl.
However, two studies in the 1970s found very small shifts in this study, showing that having sex close to ovulation resulted more in girl-child and sex on either side of ovulation resulted more in boys.
These findings made Shettle’s theory shaky leading people to cast doubts on it. Remember Shettle made his findings with inferior technology so it is possible that his findings are faulty.
Since then, there has been mixed evidence, but the findings are still disputing any effect of timing on sex selection. Perhaps the most high profile study, published by American epidemiologist Allen Wilcox, found no evidence to suggest that the timing of sex around ovulation led to a significant change in the sex of babies.
What New Research Says
There is a technology, however, for sex selection of embryos, where a number of embryos are fertilised outside, and the desired sex is put back into the womb to develop, and it is only legal for medical reasons. For instance, if a family has a disease that is peculiar to a particular sex (sex-linked diseases), this can be recommended.
Yet, it is illegal in some countries such as India as this can cause people to tilt towards a particular sex.
The truth is, boy or girl, we all matter and until technology evolves further, we will continue to learn how to determine the sex of our kids.
Good luck on your next pregnancy and may you have the child of your dreams