When Kwek Yu Xuan was born on June 9 last year at National University Hospital (NUH), her weight - 212g - was about that of an apple.

She was born about four months early, and doctors had expected her weight to be at least 400g.

After a 13-month stay in hospital, she was discharged on July 9, and is believed to be the world's tiniest baby to survive a premature birth.

When she was first wheeled into the neonatal intensive care unit, Ms Zhang Suhe, an advanced practice nurse at the department of neonatology at NUH, could not believe her eyes.

Ms Zhang, who is also a nurse clinician and would later be part of the care team for the infant, said: "I was shocked so I spoke to the professor (in the same department) and asked if he could believe it.

"In my 22 years of being a nurse, I have never seen such a small newborn baby."

The previous record holder, according to the Tiniest Babies Registry by the University of Iowa, was a girl born in the United States in December 2018, weighing 245g.

Babies like Yu Xuan who are born about four months early have a survival rate of about 70 per cent, according to NUH, and most would be discharged after four to six months in hospital. But due to her extreme small size, she spent 13 months in hospital, making her the longest-staying baby there.

Her birth came unexpectedly for her parents, Mr Kwek Wee Liang and Madam Wong Mei Ling, both 35.

The couple, who are Singapore permanent residents, had planned to return to Malaysia for the birth, so they could reunite with their four-year-old son. He is under the care of Mr Kwek's parents.

But on June 8 last year, Madam Wong, who works as an administrative assistant in an insurance company, felt abdominal pains and was rushed to NUH.

She underwent an emergency caesarean section, as she was found to have pre-eclampsia, or high blood pressure during pregnancy.

Madam Wong said Yu Xuan's birth and size came as a shock, especially because her son's birth was a routine one.

"I didn't expect to give birth so quickly, and we were very sad that Yu Xuan was born so small. But due to my condition, we didn't have a choice. We could just hope that she would continue to grow and be healthy," she added.

Yu Xuan's condition was so frail that she had to be placed on a ventilator to help her breathe because her lungs were not well developed.

Dr Yvonne Ng, a senior consultant at the neonatology department, said: "Her daily care was the main crux of the matter, especially for the first two weeks of life...We needed to innovate and find some improvised methods to deal with a baby this small because this is the first time we experienced somebody this tiny.

"She was so small that even the calculation for the medication had to be down to decimal points. "

Yu Xuan's skin was so fragile and thin that it was hard to put probes on her to monitor her condition. Leaving a probe for too long would leave a dent, which could result in a sore and an open wound, making her prone to infection.

A diaper for a newborn was too big and covered her whole body. The care team sourced for vendors that could bring in diapers that would fit her.

But when they finally found a vendor, it said it did not supply stock to Singapore. Doing so would be very expensive.

The care team decided to refashion diapers to fit Yu Xuan, such as by cutting them.

Ms Zhang said: "There are some chemicals in the diaper to absorb the baby's urine, and this can't come into direct contact with Yu Xuan's skin. So we had to fold and seal the edges... these are the things we had to do for her, because caring for her skin is very, very important."

There were other challenges as well, such as when the nurses had to insert tubes into the baby's body. The size of Yu Xuan's thigh was about that of a finger.

But despite her tribulations, she was described as a happy and positive baby, with her own quirks and preferences.

She would turn, move her hands and respond to the nurses when they called her.

Ms Zhang said: "She likes to be in a cooler environment, and when it gets too warm, she would get agitated. Sometimes she likes to have someone talking to her, and she likes pacifiers too. But she could not hold the pacifier on her own, so we had to hold it for her."

After 13 months in hospital, her condition is now a far cry from what it was when she was born. She weighed about 6.3kg when she was discharged on July 9.

The occasion was a joyous one for the hospital, Ms Zhang said, and even nurses who were off duty turned up to take photographs.

Although Yu Xuan, now 14 months old, still has chronic lung disease and has to be placed on a ventilator at home for oxygen assistance, she is able to turn on her own, and is learning how to feed from a bottle.

The hospital bill, which went up to about $200,000, was paid for through crowdfunding efforts, which raised about $300,000.

About half of the excess was set aside for Yu Xuan's future needs, while the other half was returned to the crowdfunding platform, Give Asia, for other needy families.

Madam Wong, whose husband is a technician, said the family does not intend to return to Malaysia for now, as Yu Xuan needs follow-up care from the hospital.

She said: "I have to thank the nurses for taking care of her for such a long time, they really took very good care of her. We were very happy that everyone could come for her discharge. The team is like family."