Expert fears Charlotte the virgin stingray's babies could be DEAD - as world questions why she is taking so long to give birth after 'immaculate conception'

Charlotte the stingray has disappeared from the public eye for nearly two weeks, leading people to question the validity of her supposed immaculate conception.

A marine biology expert with California State University told DailyMail.com that it is possible Charlotte's babies have died or she may abort the embryos.

Round stingrays typically have a gestation period of three to four months and the Aquarium & Shark Lab in Hendersonville, North Carolina announced Charlotte was pregnant in early February and had been for some time - claiming she would give birth any day. 

One expert suggests that Charlotte the stingray could lose her babies because she is pregnant through parthenogenesis, which means virgin birth

The aquarium said Charlotte was pregnant with up to four pups but the sonogram (pictured) appeared to show only one

The Aquarium & Shark Lab in Hendersonville, North Carolina first announced Charlotte was pregnant via immaculate conception in early February

The Aquarium & Shark Lab in Hendersonville, North Carolina announced Charlotte was pregnant in early February, saying she could give birth 'any day now,' but as time ticks on, people have become less certain.

'It is certainly possible the ray may abort or the embryos have died or be resorbed by the female and she will never give birth,' Dr. Christopher Lowe, a professor of marine biology and director of the Shark Lab at California State University told DailyMail.com.

There are two ways a stingray can become pregnant without mating with a male, Lowe previously said.

The first is because stingrays can store sperm for at least one year, but it is an unlikely scenario since Charlotte has been on her own for so long.

The more likely conclusion was through parthenogenesis which makes 'it even more probable that the embryos wouldn’t survive, as this extremely rare form of reproduction - cloning is essentially a 'last ditch effort' for species survival in situations where mates aren’t available,' Lowe said.

'So, the chances of making a viable offspring is quite low anyway.'

Mammals like stingrays and some sharks can impregnate themselves through parthenogenesis which can occur if it has been isolated for long periods - effectively producing a clone of itself.

The aquarium stopped updating the public on Charlotte's progress for nearly two weeks, despite promising to post updates every Wednesday and Saturday

Expert Kevin Feldheim told DailyMail.com that he spoke with the head of the aquarium last weekend who said they are still waiting for Charlotte to give birth

People are beginning to voice their frustration on social media that they haven't received an update on Charlotte's virgin birth since March 23. Expert Chris Lowe told DailyMail.com that the embryos could have died, paused development, or the stingray could simply be late

Lowe confirmed it is a possibility that the gestation period is longer than expected because round stingrays are cold-blooded mammals, also called ectotherms.

This means their bodies acclimate to the same temperature as the water they are living in, he said, adding: 'Gestation is faster when they are in warmer water, and slower when its colder.'

However, there is one more theory to consider - the embryos have simply stopped growing.

'Rays are capable of something known as embryonic diapause, where the embryos cease development until conditions are more suitable,' Lowe said.

For example, the embryo can wait until the female has better nutrition for it to develop or if it's too cold to develop in the womb adequately. 

'This can stretch out gestation to periods longer than normal,' he said.

Virgin births occur when a stingray has been in isolation for an extended period and clones itself to produce an embryo

This is the first time parthenogenesis has been observed in Charlotte's species and is the 15th species documented altogether, according to Kevin Feldheim, a researcher and parthenogenesis expert at Chicago’s Field Museum.

READ MORE: New ultrasound of Charlotte the 'virgin stingray' shows her pups alive and well in the womb - and she could give birth ANY DAY 

The Aquarium & Shark Lab in Hendersonville has released an ultrasound video of her pups moving their tails inside her womb

The aquarium said in early March that Charlotte was pregnant with up to four pups and it expected her to give birth soon but didn't have a precise date.

It is difficult to know when stingrays conceive because ultrasounds are usually conducted in late-term pregnancies.

Last month, Mercedes Burns, an assistant professor of biological sciences at the University of Maryland, told DailyMail.com that Charlotte’s pregnancy appears to have proceeded normally, and she expected the stingray would give birth sometime in April.

Her projection was not to be, with people waiting with bated breath for the conclusion of Charlotte's virgin birth, but if they're hoping for an answer, they may be waiting in vain.

People have previously questioned the aquarium's reports on the stingray after it reported that a shark might have impregnated Charlotte. 

More suspicions arose when the aquarium posted a picture of an ultrasound that appeared to have only one embryo instead of four. 

Feldheim told DailyMail.com that he spoke with the head of the aquarium last weekend who told him they are still waiting for Charlotte to give birth.

'Most species have a bit of variation when it comes to gestational period, so I guess Charlotte is just a little late is all,' he said.