One thing we can rely on not thinking about while pregnant is that at least we can't get pregnant again right now... right?
There is an exceedingly rare phenomenon called superfetation in which someone can become pregnant with a new embryo while already pregnant with another one.
When this happens, the person is pregnant with two babies, but they are not twins in the usual sense of the word. In the case of superfetation, one baby is older than the other, usually by a few weeks.
Don't worry, your high school biology teacher did not mislead you. Normally when someone becomes pregnant, the hormonal shift that occurs in the body stops ovulation (the release of another egg), which is why you stop getting your period when you are pregnant.
In the case of superfetation, however, for reasons not well understood, ovulation does occur again after conceiving the first baby. And if they have sex or insemination during that fertile window, they can conceive again.
This unexpected turn of events recently became the reality for a woman named Rebecca Roberts from Wiltshire, England. After receiving fertility treatments, she became pregnant—at first, there was only one baby. But according to her report to Good Morning America, at her 12-week ultrasound, Roberts learned that not only was she pregnant with two babies, but one of them was about three weeks older than the other.
Concerns with her daughter's umbilical cord prompted emergency delivery at 33 weeks (30 weeks for her daughter). While Roberts and her medical team worried about the potential outcomes, both babies are doing well after spending time in the NICU following their births. We wish them nothing but the best—what an exciting way to come into this world!
As for you, don't spend too much time worrying that this will happen to you (although if you're intrigued and kind of into the idea, that's okay too). And even if it does, it's still very possible to have a healthy pregnancy with healthy babies—and a very interesting story to tell.