You can't really get pregnant again once you are already pregnant, can you? Turns out, you can. Superfetation is where a woman conceives while already pregnant and happened to a couple recently in England.

According to an article in Insider, Rebecca Roberts and Rhys Weaver struggled to have children. After fertility treatments, Roberts found out she'd conceived. And learned three weeks later, she'd conceived again!

There are only a handful of cases where this has happened.

Roberts said that though her 'super twins' were conceived three weeks apart, they were born on the same day last September.

She may hold the record for the longest time between conceptions in cases of superfetation.

What is superfetation? Superfetation happens when a second egg is fertilized by sperm and also implants in a woman's uterus --in addition to a fertilized egg that's already done so.

Superfetation is typically unheard of though because when you get pregnant, your body releases hormones to stop ovulation and more eggs from being fertilized. Those hormones also block sperm from getting into the cervix and even prevent the fertilization of a second egg. But, in the case of fertility treatments, where a woman's ovulation is medically influenced, it can happen.

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Obviously, there are risks of superfetation since the babies are growing at different stages. The doctors told Roberts that her younger twin, Rosalie, may not even survive. Roberts was induced at 33 weeks because Rosalie's umbilical cord hindered her development. Noah, who was conceived first, weighed 4 pounds, 10 ounces and Rosalie was 2 pounds, 7 ounces.

After several weeks in NICU, the children were released right before Christmas and they are doing fabulously. Roberts shares their journey on her Instagram page, and says she's thrilled her babies are doing so amazing.

To follow and find out more, you can go here.

Image: Semmick Photo/Shutterstock