Princess Beatrice has spoken out about the “humbling” premature birth of her second daughter.

Beatrice’s daughter – Athena Elizabeth Rose – was born several weeks premature on January 22, weighing just 1.9 kilograms.

“Her feet were so small – almost the same size as the paws on one of my older daughter’s soft bunnies,” Beatrice, who is the King’s niece, wrote in a personal essay for British Vogue.

She said she endured “months of sheer worry” during her pregnancy, adding that women’s health had “been left off the agenda” in the past.

She said baby Athena was “so tiny it took more than a few weeks for the tears of relief to dry”, adding that the infant, who is 11th in line to the throne, was “doing really well”.

“Nothing quite prepares you for the moment when you realise your baby is going to arrive early. There’s so little control,” Beatrice wrote.

“The uncertainty leaves you with an overwhelming fear of the unknown.”

The royal, who earlier this month was appointed patron of prematurity charity Borne, said: “Following routine scans, we became aware our precious cargo needed close monitoring, and understood we needed to prepare for an early arrival.

“What I learnt in this process has been humbling”.

Beatrice, who is ninth in line to the throne, is married to property developer Edoardo Mapelli Mozzi.

The princess, 36, had been due to give birth in early in the British spring.

In December, she got medical advice not to travel long distances. She joined the extended royal family at church in Sandringham on Christmas Day after changing her travel plans from spending the festive period overseas, with doctors said to have warned that a premature arrival was a possibility.

“I’m extremely pleased to let you know Athena is now doing really well, I have a few more answers as to what happened, but still no precise explanation,” Beatrice wrote.

“Looking back over those months of sheer worry, I am filled with a sense of determination that more can be done to help others find answers to those questions around the complications that can lead to preterm birth – questions that defined my days (and nights) during pregnancy.”

Beatrice’s older daughter Sienna, 3, also has Elizabeth as a middle name in honour of the princess’s grandmother, the late Queen, who died in 2022.

Beatrice married millionaire property tycoon Mapelli Mozzi in a secret lockdown wedding in 2020 attended by her grandparents the Queen and Prince Philip, the late Duke of Edinburgh, after her planned ceremony was postponed because of the pandemic.

Known as Edo, Mapelli Mozzi is the son of former Olympic skier Count Alessandro Mapelli Mozzi and Nikki Williams-Ellis.

The princess, who is the elder daughter of the Duke of York and Sarah, Duchess of York, is a co-founder of The Big Change Charitable Trust.

She also has royal patronages, including the Forget Me Not Children’s Hospice, the Teenage Cancer Trust and the Helen Arkell Dyslexia Charity.

Athena is not the first royal baby to be born prematurely in recent times.

The Duke and Duchess of Edinburgh’s daughter Lady Louise Windsor was born four weeks early in 2003, with Sophie rushed by ambulance for an emergency caesarean.

-with AAP