A baby boy born with his brain outside his skull has defied the odds to survive.

Lucas Maria, from Garfield, New Jersey, is thought to be one of the first babies in the world to live after a large part of his skull was missing at birth.

Doctors warned mum Maria Santa Maria that her baby boy might not survive a day when he was born seven months ago.

The newborn was diagnosed with a condition called exencephaly, which meant his brain was exposed.

Maria, 30, found out about her son’s condition during her first ultrasound when she was 10 weeks pregnant.

At that point, medics warned he was unlikely to survive longer than a day.

“The doctor tried to explain he had exencephaly — his skull hasn’t completely closed,” Santa Maria told The NY Post.

“He said the baby’s brain was developing outside the skull, which is extremely serious, and they recommended ending the pregnancy.”

The mum-of-four said she and her husband, Augusto Santa Maria, 31, then faced one of the hardest decisions of their lives.

“I was never for abortion but we were considering the circumstances,” she said.

“It was always a battle back and forth. I was always researching everything I could about it.

“I decided even if I could be with him for even five minutes, it would all be worth it.”

Maria sat the couple’s three daughters – aged 3, 7 and 8 – down, and explained that their baby brother’s first day would likely be his last.

She talked them through what to expect, and the girls were all in the delivery room when Lucas was born.

“They were waiting for him to pass,” Maria said.

Instead, Lucas defied the odds and made so much progress in neonatal intensive care that Maria and Augusto were told they could take their son home.

Understandably, his parents were reluctant.

Lucas still had protective dressings covering his head, that looked like a “big balloon,” Maria explained.

“It was twice the size of his head,” she said.

“If that ruptured, it would be a serious emergency. We couldn’t handle him like that.

“We asked what other options we had, and that’s when the doctor came in and started explaining the surgery… and as soon as he started talking about that, we knew it was the path we wanted to take.”

Lucas pulled through the groundbreaking surgery performed by doctors at the North Jersey Brain and Spine Center.

Dr Tim Vogel and his team wanted to do all they could to grant the family’s wish — to hold their baby.

In most cases of exencephaly that isn’t possible because any physical contact risks damaging the fragile layer of cells that protect the baby’s brain.

“I had to push for the first couple days for the surgery to get done,” Dr Vogel said.

“I think it was an amazing amount of strength the family had in looking forward to that.”

Amazingly, Lucas was allowed to go home only a week after the procedure.

The little fighter will need another operation in the next five to six months, where Dr Vogel’s team will start to reconstruct his skull.

“There’s no script to follow,” he said.

“Every moment that we have with Lucas is a blessing, so I don’t know what he’s going to be able to do.

“The fact that he’s able to do what he’s doing now is incredible.”

Lucas has been going to physical therapy, as well as eating cereal and baby food, his mum said. And his sisters enjoy singing to him and kissing him.

“He came to complete our family because this is the baby boy we’ve been waiting for,” Maria said.