A mother who conceived her two daughters in the same week has spoken out about the incredible and extremely rare phenomenon, which saw her fall pregnant with her second child while she was already pregnant with the first.
Odalis and Antonio Martinez, a couple from San Pablo, California, US, were thrilled when they found out they were expecting a child in November 2020 after suffering a miscarriage in July during their 12-week check-up.
Ecstatic that they had fallen pregnant again, the couple were not expecting any more surprises - until during her first ultrasound appointment at 12 weeks gestation, 25-year-old Odalis was stunned to discover that the stork had been working overtime. She was carrying not one, but two babies.
The rare event, known as superfetation, is when a second, new pregnancy occurs during an initial pregnancy. Another ovum, or egg, is fertilised by sperm and implanted in the womb a few days, or sometimes weeks, after the first conception. Babies born from superfetation are typically considered to be twins as they are often born during the same birth or on the same day.
Odalis was told that her two babies had been conceived at different times during the same week - an occurrence the young mum believes is a "miracle".
"I just say that they're twins, but after reading a lot of articles I know that they're technically not twins, but it's just confusing for people," Odalis told local media, as reported by The Sun. "So I just tell them, 'yeah, they're twins'.
"They're technically not even identical but everyone thinks that they are. They definitely look a lot alike. Sometimes me and my husband - well, more my husband - will get them mixed up with each other. I usually don't get them mixed up anymore, just because I'm with them 24/7 so I feel like I can tell them apart pretty easily."
The mum says she feels incredibly lucky to have fallen pregnant again so quickly after her miscarriage, a tragic experience that made her "terrified" for her next pregnancy.
"I felt really lucky. I know a lot of people that have been trying to conceive and just haven't been able to so that was also a fear of mine, but thankfully that wasn't our case and I fell pregnant really quickly," she said.
"I felt really, really happy and also scared because of the miscarriage. It was pretty terrifying throughout my whole pregnancy, not knowing if that was going to be the outcome again."
When Odalis turned up for her 12-week appointment alone due to COVID-19 restrictions, she was terrified that history would repeat iself - and there wouldn't be a heartbeat.
"I'm trying to mentally prepare myself for anything and when she found the first baby and the heartbeat I was crying with so much happiness," she recalled.
"And then she started going back and forth and I was wondering why - my mind just went to the worst-case scenario because of the traumatic experience that we had. That's when she told me that she had found another baby that also had a heartbeat.
"I was just crying with happiness. I felt like the first baby that we had lost was in the room with me and saying it was going to be okay."
Odalis was informed that the second baby had been conceived a mere five days after the first, a surprise she said she had "no idea" was possible.
Lilo and Imelda Martinez-Atoyac were born on August 10, 2021.
"I feel like it's some sort of miracle that I experienced this double pregnancy. Because of our first experience, it made everything during this pregnancy feel so much more special and magical," she continued.
"When I held them and knew that they were okay, I can't even explain the feeling. I love my family and my husband, but I had just never experienced love and happiness like that."
The true number of superfetation cases is currently not known, but according to a report published in 2008 in the European Journal of Obstetrics & Gynecology and Reproductive Biology, fewer than 10 instances of the condition had been recorded worldwide at the time.
In April 2021, UK woman Rebecca Roberts gave birth to twins conceived three weeks apart after she and her partner struggled with infertility for more than a year. Like Odalis, Roberts also discovered that she was a medical marvel during her 12-week scan.
Like the Martinez' daughters, Roberts' pregnancy is one of few superfetation cases recorded in medical literature.
Speaking to The Washington Post, Roberts' obstetrician, David Walker, said the condition is so uncommon, he struggled to diagnose it, telling the outlet he had never seen the occurrence before in his 25-year career.
"It just doesn't happen," he said.
"Instead of stopping ovulation, she released another egg about three or four weeks after the first one, and the egg somehow miraculously managed to fertilise and implant in her uterus."
