A woman gave birth to twins conceived a week apart after she fell pregnant with a second baby while already expecting.
Odalis Martinez De La O, 26, fell pregnant with her first baby on the last day of her menstrual cycle - before she conceived a second five days later.
The mum-of-two was told by the ultrasound doctor babies, Lilo and Imelda, now aged one, were ‘measuring differently’ and had been conceived at different times.
The rare phenomenon is called superfetation and is “extremely rare”.
It happened after she released two eggs instead of one during her cycles – and both were fertilised by different sperm.
The fertilised egg then needs to implant in an already pregnant womb; if all three of these happen then superfetation occurs.
Even medical professionals were confused when Odalis took her twins to their first doctor’s appointment, she said.
Odalis, a programme manager, from San Francisco, California, US, said: “I was definitely shocked.
“Firstly, because it was twins, and secondly, processing the fact that they were conceived five days apart.
“I’ve never really known how twins work so I didn’t know that could happen – it was a really great surprise.
“We had a miscarriage the first time we tried, so getting the news that it was two was beautiful.
“All my family were asking how that can happen, we were all so shocked.
“It’s good information to know about. I’m telling all my friends to be careful now!”
Odalis and her husband, Antonio, 32, a university programme director found out they were conceived at different times in January 2021 after a check-up revealed that both of the twins were measuring differently.
They welcomed Lilo and Imelda via Caesarean section into the world on August 10 2021.
Lilo was conceived first, with Imelda conceived five days later and despite not being identical twins, Odalis says to some people they look alike.
Odalis says Imelda looks bigger but every time they go to their doctor they are told the babies are equally as heavy.
She said: “They both have always been in the 97 percentile so are pretty big babies!
“I can definitely tell them apart, but they have some days where they look extremely alike.
“But if you ask people who don’t see them every day, they say they look the same.”
Upon taking the twins to their first medical appointment, they told the doctors that Lilo and Imelda had been conceived five days apart.
Odalis says the doctors asked her what she meant and that they hadn’t heard of it before.
She said: “It was a student doctor that came and spoke to us.
“I said the babies were conceived five days apart and she was confused and went and got the senior doctor and even she was like ‘what do you mean?’ And she said she hadn’t heard of it.
“I think even the ultrasound nurse was a bit confused too but did her best to normalise the situation.”
Odalis took to TikTok to share her rare experience, where the video racked up over 1.5 million views and attracted plenty of interest from other users.
One said: “Yes mine are 14 days apart both girls two different dads - try explaining that.
Another said: “I didn’t know you could conceive twins days apart!! TikTok teaches me something new every day.”
Whilst a third added: “What! I had no idea this was possible.”
