In 2021, an Australian woman found out that she was having twins. Not by itself news that would make headlines. But when the expected mother checked in with her doctor, the medical professional was left stunned by what he found.
You see, the two fetuses fell neither under the identical nor the fraternal twin’s category. Instead, they made up an incredibly rare set of Residencial twins.
Nevertheless, for the Australian woman at the center of this story, her path to motherhood began in a typical fashion. Indeed, in February 2021, the BBC reported, doctors at the Royal Brisbane and Women’s Hospital are saying that she had become pregnant naturally.
And as with most mom shows, the woman in question underwent the usual pregnancy scans to ensure that the fetuses had begun to grow healthily. In most cases, medical professionals employ ultrasound imaging to examine the womb and identify any potential birth defects or similar issues that could be present in a fetus. Ultimately, then, was during this routine procedure that Professor Nicholas Fist noticed something unusual about the Australian mom’s offspring.
At first, Fist said, the woman’s pregnancy seemed to be charting a very traditional course. The mother’s ultrasound at six weeks showed a single placenta and positioning of amniotic sacs that indicated she was expecting identical twins, he told the BBC. In time, however, Fist noticed a single detail on the screen that proved the fetuses couldn’t be identical. Parents of multiples will almost always find that they’re expecting one of two different types of twins, monozygotic or disagree. In any pregnancy, you see sperm fertilizer at least one egg to create the zygote cell.
Sometimes, though, this cell will split into two embryos. And because the embryos come from the same cell, they have the same DNA. As such, monozygotic twins tend to appear as identical as their DNA and are both of the same genders. Despite the similarities in the twin’s appearances, however, they will have different fingerprints. Why?
Well, as each baby grows in the womb, they feel around their environment and gather unique markings to differentiate the grooves on their digits. And across the planet. Approximately zero to 3% of birds see a set of identical twins in the world. What’s more, the likelihood of a woman having lookalike babies is the same everywhere on the planet. Although this isn’t the case when it comes to psychotic or fraternal twins.
Fraternal twins are also known as nonidentical twins, suggesting, of course, that they do not end up looking the same. That’s large because the two babies grow from separate eggs fertilized by different sperm cells. And as such, each twin possesses distinct DNA. The pair just happens to share the woman and arrive at the same time. So while fraternal twins can still come out as spitting images of each other, indeed, this can happen with siblings of any kind.
Their unique DNA means that they can also look different and then there’s the possibility of boy-girl dizygotic twins as well, which isn’t the case with identical pairs plus instances of fraternal twins don’t have a universally uniform distribution. Instead, different areas of the planet inexplicably have more disagreed twins than others. Japan has about six sets for every ten deliveries, for example, while areas of India have 15. And in some spots in central Africa, more than 20 births per 1000 bring two bouncing but not generally identical babies into the world. It’s worth noting, too, that fertility treatments and medications have boosted the number of fraternal twins.
Typically, these drugs cause mothers to hyper ovulate, which means their bodies emit numerous eggs at once. It’s the perfect scenario, then, for more than one embryo to form. And because of this phenomenon, the numbers of multiple verses from twins to triplets to quadruplets and beyond have spiked in the US. With all of this information in mind, then it becomes easier to understand why Fist found himself confused when he performed ultrasound for the Australian mom to be in 2021. At first, the doctor saw a pair of antibiotic sacks that were each on the same placenta usually a surefire sign that the mom would have identical twists.
After that, Fist told a mom that she’d have to come back for another checkup to determine the sex of her fetuses, although it may have appeared safe to assume that there will either be two boys or two girls. But at the mom’s 14-week ultrasound, Fist found himself facing the unexpected. Yes, the mom had one boy and one girl on the way, even though the fetuses were growing in a monozygotic manner. And according to a March 2019 report by the New York Times, Fist thought to himself at that moment, it doesn’t add up. Eventually, though, he realized that he had overlooked a third twin category one so rare that there’s only one other recorded instance.
Specifically, Fist discovered that the twins were semidenical, also known as sasquizagae. Therefore, the fetuses had formed after one egg in their mother’s womb had been fertilized by separate sperm. And as a consequence, while the twins each shared differing amounts of their father’s DNA, they both had 100% of their moms. Broadly, they are about three-four identical, Fist told the New York Times, before adding that such a situation is almost as rare as hen’s teeth. In theory, you see, such a conception shouldn’t be feasible, especially considering the two ways in which twins typically form.
In both scenarios, one sperm plus one egg equals one baby. When a sperm enters an egg, the membrane locks down to stop any other sperm from getting in, Fist explained. Even if another sperm got into an egg, you would end up with three sets of chromosomes. And owing to this excess of genetic material, Fisk added, the resulting fetus ultimately wouldn’t survive. But semi denial twins nonetheless occur because they each somehow receive only the amount of genetic information they need.
Some of the cells contain the chromosomes from the first sperm while the remaining cells contain chromosomes from the second sperm, Fisk’s colleague Dr. Michael Gabbat explained to CNN in March 2019. As such, Gabbott said, this resulted in the twins sharing only a proportion rather than 100% of the same paternal DNA. And in fact, staff at the Royal Brisbane and Women’s Hospital embarked on a painstaking examination of each twin’s DNA, comparing all of the female fetus’s chromosomes to her brothers. In some stretches of the twin’s DNA, they shared the same genetic information.
In other parts, though, they were different. Ultimately, then, this amounted to the fetus sharing approximately 89% of their DNA, and the process also may Fist, the first doctor to identify semi identical twins during their mother’s pregnancy. The only other recorded case of semi identical twins occurred in 2007. In that situation, however, the female twin required medical care because she had what is termed ambiguous genitalia, and when doctors examine the female fetus’s genetic comb, they realize that she and her twin had identical DNA from their mother, but only about 50% of the same code from their father. Neither of the Australian twins had to face this hurdle, though.
Indeed, they came into the world healthy, and as Fist told the New York Times, they continue to thrive at age four. They’re doing well in meeting their developmental goals, he said. Still, once Fisc and researchers from two Australian universities realized that they had this rare set of semi identical twins on their hands, they couldn’t help but wonder how many other Sasquatch, iconic babies existed out there. Sure, there was the 2007 case, but they thought that other twins may have been misidentified, or perhaps that their very DNA may not have been chronicled. So, to prove the rarity of the semi identical twins, Fisk and his colleagues from the University of New South Wales and the Queensland University of Technology went on to examine the DNA of close to ten sets of fraternal twins.
And Fisk went on to describe the monumental test at CNN, saying, we needed to confirm the results with really exhaustive studies in multiple labs in multiple States and countries and with tests involving millions of genetic variants. Then, with the investigation finally complete, the team could be sure of their initial notion. The semi identical twins delivered in Australia were indeed extremely rare. Nevertheless, before the researchers shared their findings through the New England Journal of Medicine, they had to be thorough, Fisk later acknowledged to CNN. We needed to convince, rightly skeptical reviewers that this data was robust.
And as it turned out, the group’s work piqued the interest of other sets of twins. Indeed, Fist told the New York Times that he had received numerous emails from those who thought that they and their twin may have gone through life without knowing they were more than just a fraternal pair. But of course, even with fiscal teams finding, many questions remain about Residencial twins. Doctor Mindy Christensen of the Johns Hopkins School of Medicine said that the research may have only scratched the surface of what can happen when twins are conceived. The recent case was detected because the twins were male and female, Christensen told the New York Times.
