Having one set of identical twins is rare enough, but Simone Burstow just gave birth to her second set. The 32-year-old from Brisbane, Australia, welcomed daughters Evie and Georgia on September 4—and she’s already mom to 4-year-old identical twins Harrison and Oliver.
Burstow and her husband conceived both sets of twins without reproductive assistance, and she was shocked to discover at her six-week ultrasound that she was having twins again. “I was laughing and crying,” she told Us Weekly. Her boys, on the other hand, weren’t as blown away. “I think they thought it was somewhat normal to have babies two [at] a time,” she says. “They weren’t particularly amazed or impressed.”
Here’s an adorable photo of Burstow and her husband with their baby daughters:
And here’s a sweet snap of Harrison and Oliver getting to know one of their new siblings.
The odds of having identical twins, which happens when a single fertilized egg splits in two, are about three in every 1,000 births, multifetal pregnancy management expert Michael Cackovic, M.D., the obstetric director of the maternal cardiac disease in pregnancy program at The Ohio State University Wexner Medical Center, tells SELF. And although no one knows the exact chances of a woman who already had identical twins having a second set, based on those statistics, it would be in the neighborhood of 1 in 110,000—so, pretty rare.
Jessica Shepherd, M.D., an assistant professor of clinical obstetrics and gynecology and director of minimally invasive gynecology at The University of Illinois College of Medicine at Chicago, agrees, telling SELF that Burstow’s situation is “incredibly rare,” especially given that she had identical twins, which are more unusual than fraternal ones. Fraternal twins happen when a woman releases two eggs, which are then fertilized by two different sperm (that’s why they’re known as “dizygotic” twins whereas identical twins are called “monozygotic”). It’s more common for a woman to release two eggs at once than for an already fertilized egg to split. “The splitting of an egg for identical twins is quite a phenomenal occurrence,” Shepherd explains.
While experts think your odds of having identical twins a second time don’t change if you’ve had them once before, you’re more likely to have fraternal twins again if you’ve already had them, Stephen Thung, M.D., chief of obstetrics at The Ohio State University Wexner Medical Center, tells SELF. “If you have had previous dizygotic twins, you will have an increased [chance] of having another set when compared to women who have had singletons,” he says.
Shepherd says a history of fraternal twins on the maternal side can increase the chances of someone having a pair themselves. So can ethnicity (women in Nigeria are much more likely to have twins than those from China, for example). A woman’s age is also a factor, Jennifer Hirshfeld-Cytron, M.D., of Fertility Centers of Illinois, tells SELF. “[Fraternal] twins are more common nearing the end of maternal age due to changes in the body increasing the number of eggs released during ovulation,” she explains.
As for why someone might have identical twins again, experts just aren’t sure. “The mechanism of identical twins is fairly obscure,” Cackovic says.
Burstow says she and her husband were pretty overwhelmed at the idea of having two sets of twins at first, but now she says they’re thrilled. “The best part about twins is watching their bond develop right from the start,” she says. “Even with the girls being a couple of weeks old, they hold hands when they are tandem feeding and just look at each other when they’re lying down…it makes all the hard work worthwhile.”
SELF – Culture