When most pregnant women are asked how far along they are, it's typically an easy question to answer, but that wasn't the case for one expectant mother. That's because one of her babies was two-and-a-half weeks older than the other. Her name is Sandra Searle from Perth, Australia, and she had what is known as superfetation twins.

The rare condition happens when a pregnant woman gets pregnant again. For Sandra, it occurred because she and her husband were using IVF, which they had success with for their first two children. Because her husband was a testicular cancer survivor and she had been told she had a low egg count, conceiving naturally was extremely unlikely, however, she wound up getting pregnant, though she didn't know that when she went through an IVF cycle, which also worked.

Soon after, Sandra's doctor noticed abnormally high hormone levels and called for a scan, which, according to Australia's ABC, he said showed "a seven or eight-week sized fetus, which was about 18 days ahead of where it should have been, plus another little sac which was consistent with the really early pregnancy from the IVF cycle." He added, "She's managed to get herself pregnant spontaneously with really no supporting hormones, then the IVF embryo stuck at the same time."

While the news was surprising to the Searles, it was even harder to explain to others. Sandra said, "Firstly, I was trying to wrap my head around being pregnant with two babies with two different gestations. So I was continuously having to explain to medical experts that I was expecting two babies... with one baby at six weeks and one baby at eight and a half weeks. And nobody could understand why."

The different ages of her babies made a due date hard to decide on. Her doctor described the situation saying, "Between 36-and-a-half weeks and 39 weeks, there's a lot of change going on in babies. At 36-and-a-half weeks, babies are much more likely to end up in the nursery with some breathing problems needing some extra support. And generally 39-week babies come out and they're ready to go. So trying to work out the optimal time for both and trying to work out what's going to be best overall is always tricky."