Rare conjoined twins who survived separation surgery despite just 2% chance of survival have graduated kindergarten.

Mum Heather Delaney, 33, learned at just 11 weeks pregnant that she was carrying conjoined twin baby girls.

Connected at the head - known as craniopagus twins - the babies had a low chance of survival, but fought against the odds.

Heather gave birth to daughters Abby and Erin at 30 weeks in July 2016 - who weighed 6lbs combined.

Heather and her husband, Ryley Delaney, 30, a landscape foreman, were thrilled despite the their daughters having to remain in the neonatal intensive care unit at Children's Hospital of Philadelphia (CHOP), Pennsylvania - ten hours from home.

In June 2017, the girls underwent a rare, pioneering procedure to separate their skulls - and despite the risks, the 11-hour-long operation at CHOP, was a success.

Although both little girls have developmental difficulties, they are both thriving now as they approach their seventh birthday.

Proud parents Heather and Ryley watched their girls graduate kindergarten earlier this month - a milestone doctors doubted they'd reach.

Heather, a stay-at-home mum, from Statesville, North Carolina, US, said: "There are days now where I sit back and think 'I cant believe how incredibly lucky we are'.

"Yes, they have disabilities and things they're working through, but they're so happy.

"Watching them graduate, it was like we were dreaming.

"It's one of those things where you feel like it'll never come.

"We don't yet know what they can accomplish so the sky is the limit for them.

"Although they don't remember, they see photos in the house of when they were conjoined.

"One day we'll sit them down and talk about it properly - we want them to be proud of who they are and where they've come from."

New parents Heather and Ryley feared the worst when they learned they were having conjoined twins just 11 weeks into the pregnancy.

Doctors told them the chance of having craniopagus twins in the first place - where they're joined at the head - was one in 2.5million.

Despite being told of the 2% survival rate, the parents were told their girls might be candidates for separation surgery once born.

Heather was admitted as an inpatient from 27 weeks but went into labour naturally at 30 weeks.

Abby and Erin, joined at the skull, were born via c-section at 1:02am on July 24, 2016, at Children's Hospital of Philadelphia (CHOP), in Pennsylvania, US.

Heather said: "When we first found out we went into shock first, we had no idea what to think.

"It's something you only see on TV, I thought this doesn’t actually happen to people."

Abby and Erin shared a skull, skin and their superior sagittal sinus - a critical vessel which carries blood away from the brain.

Together they weighed around 6lbs and had to remain in the NICU in Philadelphia until their separation surgery the following June.

The separation surgery would be the first of its kind to ever go ahead at the hospital - due to the rarity of the girls' condition.