I know reading fiction requires a certain amount of suspension of disbelief, but nothing brings a fictional world crashing down around me faster than simple factual inaccuracies.
Vampires? Sure. Superheroes? Why not. An overnight high school field trip with only male chaperones? Yeah, no. (Lookin’ at you Spiderman: Far From Home)
Which is why when the solution to the mystery novel I was reading (ok, listening to) revolved around a set of identical male/female (AMAB and AFAB) twins, I balked.
(In fairness to the author, I looked it up just to be sure, and apparently there has been a case where this happened, but the AFAB child was technically intersex, due to a genetic mutation, resulting in XXY chromosomes – which was not the case in the book, as far as I could tell).
So, as a writer, a Ravenclaw, and the mom of identical twins, I thought I’d list off some facts about twins that you may or may not know.
- Identical twins occur when the (already fertilized) egg splits. The twins are genetically identical.
- Fraternal twins occur when two eggs are released and subsequently fertilized by separate sperm. These twins can be any gender combination and are only as similar as regular siblings.
- There is a third type of twin where the egg splits before being fertilized, so the twins are 3/4 genetically identical. Mary Kate and Ashley Olsen are believed to be this kind of twin.
- Identical twins can share an amniotic sac (at high risk for cord entanglement), and/or a placenta (those who share a placenta are at risk for Twin-to-Twin-Transfusion Syndrome, where one twin steals nutrients from the other).
- Twins make up 3/100* births. Identical twins occur in 3/1000* births.
- No one knows what causes identical twins. Fraternal twins can run in families (due to a genetic disposition to release multiple eggs), can be a result of fertility treatments, or can occur when the mother is older than 35 (as the body releases more eggs with age – 17% of mothers over 45 have twins, mothers over 50 have a 1 in 9 chance of twins).
- Giving birth to twins increases your risk of having twins again (applies to both fraternal and identical twins).
- Twins can have different birthdays. In the time between birthing one twin and the next (minutes for a C-Section, up to hours for vaginal birth) the clock can tick over from one day, month, or even year to the next. In some cases of illness or premature labour, doctors can halt the birth process after one twin is delivered, leaving the second to be born as late as weeks later.
- Identical twins can have different fingerprints.
- Identical twins can develop differently (my sister-in-law’s identical twin brothers have a few inches of height and tens of pounds separating them).
- Some identical twins (including my own) are mirror twins – instead of being truly physically identical, they are mirror images of each other (Mine even write with opposite hands, cut opposite teeth – eg. front left for one, front right for the other – and had opposite pointed ears at birth).
- If identical twins have children, those children are genetically half-siblings (as well as cousins). If they have children with another set of identical twins, those kids are genetically full siblings.
*These numbers seem to vary from site to site, so I went with the ones that agreed with those my doctors told me.
- A whole lotta pregnancy books and doctors.