While being both incredible and life-changing to hear the news that you’re expecting a baby, pregnancies can be difficult. From the physical changes to your body that you couldn’t begin to prepare for, to the possible morning sickness during your first trimester, becoming pregnant has its downsides.

Despite how complicated, it’s usually worth it, even for those parents who give birth to preemies and endure a daily battle until their baby fully develops. But for one couple living in Australia, they experienced a pregnancy that not many others can say they have been through…

Polycystic Ovary Syndrome

Shortly after Kate and Peter got married in 2006, a doctor told Kate she had a serious problem. She was diagnosed with polycystic ovary syndrome, which is a syndrome which can make conception difficult. Basically, it meant that Kate wasn’t ovulating and her body had a hormonal disorder.

Conceiving Would Be Hard

Like others with the same condition, Kate’s ovaries could develop numerous collections of fluid and fail to regularly release eggs. Unfortunately, polycystic ovary syndrome is so common that it affects one in 10 women of childbearing age. Kate just happened to be one of the unlucky ones and she shared the devastating news with her husband…

Given Hormones

As disheartening as this news was for Peter to hear, Kate’s doctor put her on hormone treatment so that she’d increase their chances of conceiving. Kate and Peter remember very distinctly that during that time, they only had sex once, but apparently it was enough.

Conceiving Twins And A Medical Miracle

Kate became pregnant and the couple was elated. From there on, they received positive news when they discovered that Kate had conceived twins! Unfortunately, one of the babies didn’t develop, but 10 days later, a medical miracle happened…

A Double Pregnancy

The couple learned that they were expecting again. But, how was this possible? Kate was already pregnant. Kate literally got pregnant while she was already pregnant, and yes, even after she, unfortunately, lost one of her twins.

Conceived On Two Different Dates

Since she pregnant on two different days, the fetuses developed at different rates. A pregnancy like this is called superfetation, and it’s extremely rare. Even rarer because the couple only had sex once…

Her Body Released Another Egg

“I had fallen pregnant and my body had spontaneously released another egg, giving the embryos different gestational ages,” Kate Hill said. “What makes this case even rarer is that my husband and I only had intercourse one time [in the possible time period of conceiving the girls].”

Decided To Search Google

Basically, Peter’s sperm stayed alive for 10 days to fertilize the second egg released. The parents-to-be were so shocked by this news, that they searched Google to get some answers for what seemed to be a medical mystery…

Barely Any Medical Literature On The Phenomenon

However, Peter couldn’t find any medical literature about the phenomenon. Apparently, there are only 10 medically documented cases of superfetation in the world, that’s how rare this type of pregnancy is. Kate was now carrying two babies, conceived 10 days apart.

Superfetation Is Extremely Rare In Humans

Dr. Jason James, medical director at Miami’s FemCare Ob-Gyn, says that superfetation occurs in some animals like rabbits and rodents, but that it is “exceedingly rare” in humans. Most doctors believe that alleged reports of superfetation are due to unequal growth and development of twin fetuses of the same gestational age. Still, despite its rarity…

Superfetation Is Poorly Understood

Superfetation is theoretically possible, at least until the uterus closes after the egg and sperm unite. This is usually by day 10 of a pregnancy, according to Dr. Michael Cackovic, who works at Ohio State University Wexner Medical Center. Despite the little information that is known, superfetation is still poorly understood and somewhat mystical in the medical community.

First Reason

Superfetation is so unlikely for a few reasons. First, after getting pregnant, your body is supposed to stop further ovulation. This means that there shouldn’t be a second egg, unless both were released simultaneously, as with fraternal twins. Plus…

Second Reason

Since the couple only had sex once, this suggests that his sperm apparently lived for 10 days inside of her before fertilizing another egg. This is also baffling because sperm can usually only live inside a woman’s body for up to five days. “That’s some super-sperm,” Dr. Sherry Ross, an obgyn said.

Third Reason

Then, because a mucus plug forms during pregnancy to prevent sperm from entering the cervix, the uterine lining usually undergoes changes that make it unfavorable for a new embryo to be implanted. “But nothing is so black and white that it’s not possible,” Ross explained…

“Life Finds A Way”

Cackovic even compared Kate’s pregnancy to a theme in Jurassic Park. “One episode of intercourse with two pregnancies 10 days apart is highly suspect. That being said, as they say in Jurassic Park, ‘life finds a way.’” But throughout the pregnancy, Kate had some concerns.

Different Weights

She was constantly worried about her babies growth and how much smaller baby No. 2 would be. Although the babies were given two different due dates, December 20 and December 30, both were delivered on November 29. As Kate anticipated, Olivia, baby No. 1 weighed 5.46 lbs and Charlotte weighed slightly less at 4.23 lbs. They also had totally different blood types…

Different Personalities

There were other noticeable differences in behavior between the girls. Olivia generally hit milestones before Charlotte, although Charlotte was never far behind her sister. Both girls are nonidentical twins, so it’s understandable how they are so different.

Their Favorite Is Minnie Mouse

While Charlotte is cautious when it comes to exploring, Olivia is more inquisitive and loud. But, there’s one thing both girls can agree on: They’re obsessed with Disney! Kate explained that they’re having a Minnie Mouse-themed party for the girls and they couldn’t be more excited.

Other Parents Shouldn’t Worry

Hill’s extremely rare birth is being studied by medical professionals. As far as what other parents could expect, Ross says that there are a lot of things that can happen that don’t make biological or logical sense. However, “you shouldn’t worry that you’re going to suddenly end up carrying two babies during a pregnancy due to superfetation.”

Medical Mystery

James also agrees, saying, “This is very rare, though we do think it has happened from time to time.” However, “when it does happen, no one is really sure how or why.” It’s a mystery.