People Are Just Realising This (Pretty Wild) Fact About Dads And Placentas

Graphic content: this article includes a photo of a placenta after birth. 

It all began when model and actress Sophie Sumner shared a TikTok video in which she spoke about her friend who’s pregnant.

“She was telling me that the placenta – which gives nutrients to the baby, it is like core to growing a baby – is 98% the man,” said the model in disbelief.

“I’ve asked a few men and they had no idea about this,” she added. 

“But I think men should know about this because it means before a woman gets pregnant, the guy needs to go on a real health kick…”

Her video, which had almost 3 million views at the time of writing, was later remixed by NHS surgeon Dr Karan Rajan, who confirmed that “there is one very important aspect of baby-making that is mostly the father’s responsibility: the placenta”.

The doctor said the placenta’s growth is “mostly influenced by the father’s genes” and described pregnancy as “a massive internal land grab”.

He concluded the video: “Despite the biological reality, society still continues to act as though pregnancy is solely the woman’s responsibility and burden – but building a human tamagotchi is not a solo project.”

Is it true?

Dr Victoria Male, a senior lecturer in reproductive immunology at Imperial College London, told HuffPost UK said she’s not sure where the statistic that the placenta is “98% the man” comes from. But she does agree that a father’s genes “are important for growing the placenta”.

Why is this? Well, first of all, we need to think about the biology of mammals in the wild or humans in the deep evolutionary past. Dr Male explained: “In pregnancy, the mother’s and father’s genetic interests are not exactly aligned.”

The expert suggested it’s in the mother’s best genetic interest for the baby to be born and survive, but she doesn’t want to give all her energy and resources to the baby.

But it’s in the father’s best genetic interests for the baby to take as much energy and resources from the mother as possible (because he can simply make more babies with other mothers).

“The placenta is at the frontline of this battle of the sexes,” said Dr Male.“The father’s genes will try to make the placenta as big as possible, to extract as much energy as possible from the mother. The mother’s genes will try to prevent the father’s genes doing this.”

Most of the time, this tug of war results in a sensible compromise – “the placenta extracts quite a lot of energy and resources from the mother, but not all of them,” said Dr Male.

One way in which the mother limits the size of the placenta is by contributing genes that favour the development of the baby over that of the placenta, explained the expert.

And there are also cells in the lining of a mother’s uterus that appear to limit how much the placenta can invade (basically, so it doesn’t keep invading).

“We can see this if we look at pregnancies where the embryo has implanted outside the uterus (an ectopic pregnancy) or on the scar from a previous C-section, where the lining of the uterus is replaced by scar tissue (placenta accreta),” she explained.

“In both these cases, the placenta will continue to invade through the uterus or fallopian tube, and out the other side, rather than stopping where it usually would. This is why ectopic pregnancies and placenta accreta are so dangerous: the placenta keeps invading and the mother can bleed to death.”

Should men alter their lifestyles before trying for a baby?

In short, yes. “There is good evidence that lifestyle alterations in prospective fathers can increase the chance of conception and decrease the chance of a miscarriage,” said Dr Male.

“However, lifestyle changes affect many aspects of male fertility, so it is hard to unpick how much of the benefit is mediated specifically by a ‘healthier’ placenta.

“We do know that drinking too much alcohol, smoking and being overweight reduce sperm count and quality. So making these lifestyle changes can help product healthier sperm, making it more likely to meet the egg in the first place.”

There is some evidence that fathers smoking before conception can increase the chance of miscarriage, too.

“That could be an effect on the placenta, but it’s more likely to be because it increases the chance that there is a genetic problem with the whole pregnancy (both the baby and placenta),” said Dr Male.

Ultimately, she suggested “it is a good idea” for future fathers to be in good health before trying to conceive, “but this is helpful for sperm count, quality and producing a genetically healthy baby and placenta that will not miscarry, rather than for the placenta specifically”.

Fascinating!