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Thursday 30 January 2020

Determining the Sex of a Baby (Things We Don’t Know about Pregnancy Series #12)

“And do you know… what it is?” they ask.

They mean the sex of our unborn baby, of course.

There isn’t much you can find out about who your unborn baby is, but you can know their sex. Or can you?

Often misnamed as “gender”, sex primarily relates to the organs a person presents with, but we already know that it’s more complex than that.

Chromosomes via Wikipedia Commons.
For a long time, we believed that sex was determined by a single chromosomal pair: XX or XY, but recent research has shown that the expressions of a bunch load of other genes is important too. For example, genes known as “enhancers” regulate the expression of genes that drive the development of physical sex characteristics. This means you can develop testes if you have an extra copy of the enhancers, even if you have two X chromosomes, or develop ovaries if you’re missing them, even if you are XY. The enhancers were found amongst the set of DNA formally known as “junk DNA”. These findings imply that observed biological sex and genetic sex may actually be different in some cases.

There’s also some controversy surrounding the question of the whether there are sex differences in the brain and, if there are, whether these are formed before birth or socialised into us: also known as nature versus nurture.

We know that our brains are very plastic and change throughout our lives depending on our experiences, especially when we are children – and boys and girls experience different upbringings – or, in other words, they get “gendered”: whether we mean to or not, adults treat different sexes differently, choosing dolls to play with girls and cars to play with boys[1][2]. This means that the expectation that little girls will prefer books to sums may be a self-fulfilling prophecy, and that skills that we associate with genders may be taught in (we know that the ‘stereotype threat’ of being told what we are and are not good at actually affects performance)[3][4]. Research has even shown that bringing up boys changes the father’s brain in a different way to bringing up girls[5]. Without testing genderless people or those from another society, this puzzle remains impossible to untangle.

The brains of trans people are sometimes completely unique. BruceBlaus [CC BY 3.0], via Wikimedia Commons.

Looking at the brains of trans people, however, is very interesting. Whilst certain brain structures have commonly been associated with males and females, it has been found that for brain volume and connectivity amongst trans people

- some have brains like the cisgender males/females with the same biological sex
- some have brains like the cisgender males/females they identify as
- some have brain in between cisgender males/females
- and some have entirely unique brains

And this is true both before and after transitioning!

These findings cast a giant question mark over that strange American tradition of gender reveal parties (where a box of coloured balloons is opened, or a coloured cake sliced to uncover whether a blue or pink baby is anticipated). Is the tradition really supposed to show what they are – or what their parents are going to make them into? So ingrained is the idea now that girls are pink and boys are blue that it’s surprising to reflect that these colours actually have nothing to do with sex or gender, but were a 1940s marketing tool that has become as much of a ritual as white wedding dresses.

Blue is for boys and pink is for girls - a marketing tool of the 1940s. Creative Commons.
After all, sonographers can get sex wrong. Whilst 60% of women want to know the sex of their baby, not all foetuses cooperate, and in some cases turning the baby to see its sexual organs isn’t possible. Mistakes tend to happen when the umbilical cord gets in the way, or the baby has its legs crossed. Accuracy only rises to 100% after 14 weeks gestation, with a success rate starting at 75% during the 12-week scan[6]. Whilst this is just an irritation to many, some women do need to know the biological sex of their baby where they may be carrying a serious genetic disease that affects one sex. For these women, invasive techniques may be used to collect foetal DNA, which can increase risk of miscarriage, so increasing ultrasound accuracy could save lives. Possible develops include cross-section imaging (allowing us to see “through” legs that are in the way).

If our fixation on our baby’s sex wasn’t weird enough, we may be able to change our biological sexes. Certain drugs that affect or supply hormones can make males look more female and females look more male (sometimes reversibly and sometimes irreversibly), as can certain genes. For instance, the genes DMRT1 and FOXL2 maintain sexual characteristics during adulthood, which means if they switch off, your gonads could change. In other words, without these genes constantly active, sexual identity could be fluid.

We chose to find out “what” we were having, but haven’t told anybody. After all, not only do we want to avoid being muffled under piles of baby pink or baby blue dollies and choo-choo trains, we wanted to make our own minds up about names. …But it doesn’t stop people guessing!

“You’re carrying high; it must be a girl,” Cerys from work tells me.

“It’s definitely a girl,” Karen, my husband’s colleague, tells him. “You’ve given yourself away.” And then, a few weeks later: “I’m 100% sure you’re having a boy.”

Amusingly, two names on our final shortlists are gender neutral. Although we have considered one only for a girl and one only for a boy, it tickles us to imagine announcing our baby’s birth, providing their name, and leaving people still wondering.

Some, of course, choose not to find out, then continue to drive themselves bananas following old wives’ tales to guess, whether it’s measuring how high you’re carrying, judging whether you like or dislike sugar more, or waving a pendant over your belly. There is no scientific evidence that any of these practices work, any more than that what they reveal would make a difference to your tiny human’s life trajectory.

I’m due in mid February, but for now, I’ll leave you guessing.

There are many unknowns when it comes to pregnancy, and over the next few months, I’ll be exploring more of them with you. Look out for my next blog post, which will be about vitamins and supplements.

Check our our full article on the things we don't know about pregnancy. This article will be updated as we add posts across the coming months.

why don't all references have links?

[1] Seavey, CA. et al. Baby X The Effect of Gender Labels on Adult Responses to Infants. Sex Roles, Vol 1., No 2, 1975. doi:10.1007/BF00288004.
[2] Delk, John L et al. Adult perceptions of the infant as a function of gender labeling and observer gender. Sex Roles 15.9-10 (1986): 527-534.
[3] Wraga, Maryjane et al. Neural Basis of Stereotype-Induced Shifts in Women’s Mental Rotation Performance. Social cognitive and affective neuroscience 2.1 (2007): 12–19. PMC. doi: 10.1093/scan/nsl041.
[4] Baker, J, and S Horton. East African running dominance revisited: a role for stereotype threat? British journal of sports medicine 37.6 (2003): 553-555. doi:10.1136/bjsm.37.6.553.
[5] Mascaro, Jennifer S., et al. Child gender influences paternal behavior, language, and brain function. Behavioral neuroscience 131.3 (2017): 262.
[6] Kearin, Manette, Karen Pollard, and Ian Garbett. Accuracy of sonographic fetal gender determination: predictions made by sonographers during routine obstetric ultrasound scans. Australasian journal of ultrasound in medicine 17.3 (2014): 125-130.

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