Noah and Rosalie shared a womb, share a birthday, and share a pretty incredible title – they are one of the world’s rarest sets of twins.
Although they were both born on the same day, the twins were actually conceived three weeks apart, meaning their mum, Rebecca Roberts, from Wiltshire, UK, fell pregnant while already pregnant.
This incredibly rare phenomenon is known as superfetation and occurs when a pregnant woman conceives again just days (or weeks) after their first conception.
‘Always three weeks difference between them’
According to Rebecca’s Instagram page, her beautiful babies are only the 14th documented case of superfetation twins in the world. They also share a pretty decent conception gap between them of three weeks.
Rebecca shares her incredible birth story on Instagram and YouTube, explaining that she and her husband struggled to fall pregnant with their miracle twins. While she was taking a fertility drug to stimulate her ovaries, doctors do not believe that is what caused the superfetation.
Rebecca and her partner, Rhys, were informed about the second baby at the 12-week scan and she described it as the “biggest shock of her life”.
“It was noticed from very early on in my pregnancy, that’s how the doctors were happy to say they were conceived at separate times. They monitored them every week, there was always 3 weeks difference between them. I went on to have many tests after their birth which backed up their diagnosis,” she shares on Instagram.
Rosalie and Noah were born at 33 weeks after Rosalie stopped growing properly. There was a very noticeable difference in sizes between the twins and even now, two and a half years later, Noah is much bigger than his twin sister.
Pregnant while already pregnant – How superfetation worksÂ
Rebecca’s pregnancy is one of the few superfetation cases recorded in medical literature. Superfetation involves two embryos that form during two separate menstrual cycles. This means a pregnant woman needs to ovulate after she is already pregnant, which doesn’t normally happen.
During your first cycle, your body releases an egg, you have intercourse, and then the egg gets fertilised and becomes an embryo. The embryo implants in your uterine lining and begins to grow. During your next cycle, the same events take place, and the new embryo joins the other one in your uterus.
This scenario is highly unlikely because of the changes in your body that prevent a new pregnancy once you’re already pregnant.
Superfetation is a bit different from another pregnancy rarity known as superfecundation. This can occur when your body releases two or more eggs during the same menstrual cycle. Each egg is fertilised by sperm, which can be from the same or a different partner or donor. We shared a story of a woman discovering this was the case with her twins.Â
The young woman had sex with two men on the same day which, surprise, means two different dads. Read her story here.
Twins to triplets
In February 2021 we shared another story of superfetation as a California mum-to-be found out she was expecting twins. However, at her 12-week ultrasound, doctors discovered a third baby, conceived 10-11 days later than the twins.
The triplets, all born on the same day, and all girls, are now crazy toddlers. She shares their antics through Instagram and TikTok.
Surrogate twins
In 2021, a surrogate mum named Jessica also got the shock of her life when she fell pregnant with another baby while carrying for another woman. Although the babies were growing at different rates, doctors didn’t think much of it. It was only after the twin boys were born that superfetation was suspected.
You see, one of the babies looked very different than the other and, as DNA testing revealed, one infant was, in fact, her surrogate mother’s biological son with her partner.
Jessica and her husband had to fight for their son through court and incurred legal fees, but, nine months later, they were finally given custody of their son, whom they named Malachi.
Twins growing at a different rateÂ
In many instances, twins or triplets can be born with very different birth weights and grow at different rates in the womb. However, superfetation is different as the conception date is actually different between the babies.
This is something doctors can determine through routine scans and ultrasounds.
Louis and Neve, for example, are twins who were born with incredibly different birth rates. Louis weighed around 1.45 kg which is quite small. Neve, however, weighed just 652 grams. This is because there was a problem with the little girl’s placenta, affecting her ability to receive the nutrients she needed to grow. Neve wasn’t expected to survive, but she did! Read their story here.Â
