Are you thinking of trying the Shettles Method to conceive a particular sex?
It might be a fun thing to try, but here’s why not to put too much weight on a theory from the 1970s that has been disputed many times in more recent research studies.
My YouTube video goes into more detail on debunking the Shettles method. I also touch upon my own experiences using the Shettles method:
I first heard of the Shettles Method whilst chatting to my group of mum friends when our first babies were around 9 months old.
Some of the other mums planning baby number 2 had heard a popular theory on how to influence the sex of your baby. Apparently, if you have sex up to 3 or 4 days before ovulation, you were more likely to conceive a baby girl. Whereas, having sex as close to ovulation as possible increases your odds of having a baby boy.
My first thoughts were that the Shettles method was a ridiculous theory. If the Shettles method held any weight, wouldn’t the whole world be aware of this magical solution to gender selection? And wouldn’t the world’s population have way more girls that boys? Because surely far more conceptions happen with sperm that have been hanging around the reproductive tract for while? The window for one try on the same day as ovulation is very narrow.
Then I looked into the Shettles Method a bit more, and discovered it was actually a real method, and it kind of made some sense…sort of.
What is the Shettles method?
In 1970, physician Dr Landrum Shettles published a book called “How to Choose the sex of your baby”. Dr Shettles had a theory that boy sperm and girl sperm had differing characteristics.
Looking at sperm closely under a microscope, Dr Shettles discovered that there were two types of sperm: Larger, slower-swimming sperm with a longer life span, and smaller faster sperm with a shorter life span. Dr Shettles assumed these two different sperm types were boy sperm and girl sperm cells.
How does the Shettles method work?
OK so, let’s start with some biology basics: we all know that the egg has an X chromosome and that the sex chromosome of the successful sperm determines the baby’s sex. If a Y chromosome sperm is first to reach the egg, a baby boy is conceived. If an X chromosome arrives at the egg first, it’s a girl baby. Statistically, the odds of conceiving a boy or a girl are almost the same.
Based on the different characteristics Dr Shettles identified between X and Y chromosome sperm, the basis of the Shettles method is simple. If you have sex close to ovulation, the faster male sperm have more chance of reaching the egg first. If you have sex earlier in the menstrual cycle, up to 3 or 4 days before ovulation, the male sperm with the shorter life span will die out by the time of ovulation. This leaves the slower but sturdier female sperm to win the race to the egg.
According to the Shettles method, The different sperm characteristics meant that different sex positions were optimal for conceiving a specific gender. A deep penetration sexual position like doggy style would be optimal for getting the male sperm closer to the egg to give them a head start. The Shettles Method recommends the shallow penetration of missionary position when attempting to conceive a baby girl.
What is the Shettles method success rate?
Dr Shettles boasts a 75% success rate. There are many positive online reviews and message board stories of sex selection success using the Shettles method.
Anecdotally, you are likely to hear from people for whom the Shettles method has worked. You are less likely to hear from people who secretly had a desired sex and found the Shettles method didn’t work. Bear in mind that this tends to skew the idea of the Shettles method as successful and accurate.
Did the Shettles method work? Or is the fact really that there is a 50/50 chance of conceiving a boy or a girl, meaning that around 50% of people will be ‘successful’ in conceiving a specific gender.
How accurate is the Shettles method?
And now for the twist in the tale. The Shettles method is not at all accurate. In fact, the Shettles Method has now been widely debunked. Let me tell you why.
Dr Shettles thought he was looking at male and female sperm. But numerous more recent studies have conclusively found that there is not actually any difference in shape between X sperm and Y sperm, and there was no evidence of Y sperm being faster swimmers.
Perhaps Dr Shettles was looking at capacitated and uncapacitated sperm (more on that in a minute). Whatever his findings, it was clear that the two types of sperm he thought he had identified were not male and female sperm.
So, it turns out that the Shettles method is possibly the biggest misconception when it comes to conception theories.
Why the Shettles method is not true
A possible explanation for why the Shettles method is simply not true is that Dr Shettles was looking at uncapacitated sperm VS capacitated sperm. Not boy sperm and girl sperm. Dr. Shettles developed his timing theory in the 1960s, before the capacitation process had even been discovered.
Capacitation in a nutshell: Capacitated sperm have lost the protective cap at their tip. They are smaller and speedy because they’re ready to fertilize an egg. Capacitated sperm don’t live too long after they lose their cap
Uncapacitated sperm are bigger and slower because they still have their protective cap. In time, they will shed their caps and become smaller and more agile. However, it’s important to note that they are both X and Y sperm.
Simply put, there may be factors that influence the sex of your baby at conception. But the Shettles method is not accurate. With advances in research since the 1960s when Shettles was developing his gender selection theory, we now know that there are no discernible differences when it comes to the size, motility, or life span of male VS female sperm.
Have there been any studies on the Shettles method?
There are many examples of scientific research disproving the Shettles method:
The clinical relevance of sex selection techniques
This 1989 study actually found the opposite of Dr Shettles theory. The Shettles method suggests that intercourse close to ovulation increases the odds of conceiving a boy, whereas sex in the 3-4 days before ovulation gives the best odds of conceiving a girl.
However, this study found that more females are conceived when intercourse occurs relatively close to ovulation, and more males are conceived when the sperm or egg is in the reproductive tract for a relatively longer time before conception.
This conception theory is similar to the Whelan method for gender selection. The fact that there are at least two opposing methods of gender selection in relation to the timing of intercourse suggests that there are no conclusive answers or guarantees if you are looking to attempt to control the sex of your baby.
Despite a slight increase in odds to the opposite of the Shettles method, it is worth noting that this study concluded that the influence of intercourse timing on the sex ratio is overall quite subtle and is not a practical method to alter the sex ratio for individual couples.
Natural family planning and sex selection: fact or fiction?
A 1991 study disproving the suggestion by Shettles that the selection of male offspring by intercourse around the time of ovulation is possible.
Timing of Sexual Intercourse in Relation to Ovulation
A 1995 study of 221 women in the New England Medical Journal found that the timing of sexual intercourse in relation to ovulation has no influence on the sex of the baby.
Sex ratio associated with timing of insemination
A 1998 study of 947 births found that the sex ratio did not vary consistently or significantly with the estimated timing of intercourse relative to the day of ovulation. This study suggests that manipulation of the timing of insemination during the cycle cannot be used to affect the sex of offspring.
New Biological Insights on X and Y Chromosome-Bearing Spermatozoa
Studies in the early 2000s and more recently in 2013 used the advanced technology of atomic force microscopy to look closely at X and Y sperm.
These studies suggest negligible or no differences between these spermatozoa in terms of ratio, shape and size, motility and swimming pattern, strength, electric charge, pH, stress response, and aneuploidy. In opposition to the findings of the Shettles method, this scientific research found that the only difference between X and Y spermatozoa lies in their DNA content.
Can you choose the sex of your baby?
Sex selection theories aside, there is really only one proven way to choose the sex of your baby. That is with in vitro fertilisation using PGD.
Pre-implantation genetic diagnosis can determine the XX embyros from the XY, and implant only those with your desired gender. PGD is a highly costly method of IVF, and is only allowed in certain countries.
Determining your baby’s sex at conception is something that we, as humans, like to think we can influence. But following the Shettles method to achieve the preferred sex of your child is the equivalent of a lucky win on a coin toss.
The reality is that the sex of your baby comes down to very simple 50/50 odds whether you conceive a boy or a girl.
More on family planning and gender
The flipside of attempting to influence the sex of your baby is potentially dealing with some big feelings if it doesn't work out how you thought it might.
Read my personal experience having four boys, how I coped with gender disappointment and why I think gender disappointment needs a new name.
All about the ridiculous and intrusive comments I receive as a parent of boys
