Assisted conception

IVF: influencing your baby’s gender?

It’s something every expectant couple will spend hours milling over. Will we be having a girl or a boy? The question may spark many discussions. Names, nursery colours, finding out now vs. waiting until the birth.

One thing is for sure; the mystery of it all is very exciting.

For couples lucky enough to have conceived with the help of in vitro fertilisation (IVF), the suspense is just the same. But – unlike couples who have conceived naturally – couples who have gotten pregnant through IVF may find that the sex of their baby is not shrouded in the same mystery.

During IVF, a woman’s eggs are collected and mixed with a man’s sperm in a lab. This allows fertilisation to occur and the healthiest looking embryo that’s produced is implanted into the woman’s womb where it can hopefully develop into a healthy baby.

But before the potential baby is transferred to the woman’s womb, it’s left to grow for a little while in the lab in a fluid rich with nutrients called a culture medium.

A research study carried out last month seems to show that the gender of babies born as the result of IVF procedures may be influenced by this fluid they are left to grow in whilst in the lab.

A selection of different culture media are available. Each is produced by a different company and has its own closely guarded secret chemical ingredient list. What’s more, clinics performing IVF procedures are free to choose whichever media they like. This means the chances of having a baby of one particular sex may differ from clinic to clinic.

Jinliang Zhu and his colleagues at Peking University Third Hospital in Beijing looked at over 4400 IVF births to see which one of four types of culture media was used in each procedure.

After looking for any patterns arising, they realised that the gender of the embryo implanted into the woman’s womb after IVF was linked to the type of culture media used in the lab.

Subtle differences in the chemical ingredient list used to make different types of culture media may tip the delicate balance that determines whether IVF babies will be boys or girls. So it appears that when it comes to IVF; maybe little girls aren’t made of sugar and spice and all things nice!

So how do the different culture media influence the gender of IVF babies?

Sleepy boy
Photo credit: Sydney Treasures Photography / Foter / CC BY

The researchers realised that when one particular type of culture media was used during IVF, 56% of babies born were boys. But when another type was used, only 45% of babies were boys.

These figures are a huge contrast to the usual 51% of male babies that are born naturally in the UK and the US!

The pattern still remained even after the researchers had ruled out the possibility that other factors such as the mother and father’s body mass index, age and their specific type of infertility might have affected the sex of their babies born after IVF.

However, the pattern was only seen in babies that had been born as the result of a type of IVF procedure known as intra-cytoplasmic sperm injection (ICSI). ICSI is carried out when a man’s sperm is not able to fertilise a woman’s egg by itself. To allow fertilisation to take place, an individual sperm is injected straight into an egg to help it along.

The researchers who carried out the study believe that the reason for their results may be down to the different ways in which male and female embryos grow and develop. Each gender grows best in its own preferred surroundings.

And because the various types of culture media all differ in the chemicals they contain – they each provide growing embryos with slightly different surroundings during IVF. One sex may grow best in one culture media, whereas the other prefers the slightly different surrounding of a different media.

However, researchers are still clueless as to why different types of culture media are linked to babies of one particular sex only after IVF procedures where a man’s sperm is injected directly into a woman’s egg.

What does all this mean for couples undergoing IVF treatment?

Regardless of how this bizarre bias towards baby boys exists, couples undergoing IVF treatment and hoping to choose the sex of their babies shouldn’t get their hopes up just yet.

In most western countries – except for medical reasons – it is illegal to choose male or female embryos during IVF. And even choosing an IVF clinic based on the culture medium it uses wouldn’t be an effective way to guarantee conceiving a baby of one sex or the other.

Despite this, it’s clear that the culture medium used in IVF may have more of an impact on babies than we might have thought. Another research study led by the same scientist showed that the culture medium can also affect the weight of IVF babies at birth.

It just goes to show that when it comes to the environment a baby is exposed to early in its life; even the slightest changes can have the biggest effects!

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