Mark Zuckerberg, 31, and wife Priscilla Chan, 30, announced birth of their baby girl, Max, at around 4pm EST on Tuesday December 1, 2015. Photo: AFP/Getty Images

Proud: Mark Zuckerberg and his wife have been open about their pregnancy - announcing it in a Facebook post with an emotional explanation of their struggles with infertility. This picture with their dog Beast accompanied the post. Photo: Facebook

The Silicon Valley billionaire and his doctor wife shared the news of the baby's birth in a Facebook post entitled, 'A letter to our daughter'.

Included in the lengthy post was the couple's pledge to donate the vast majority of their fortune to future generations. They will donate 99% of their Facebook shares - currently valued at $45 billion - to the work of a new charitable foundation, the letter claims.

That would leave them with $450 million for themselves and their new child - based on Facebook's current valuation, plus any other private wealth held by the couple.

The letter was accompanied with a picture of the proud new parents tenderly holding their newborn wrapped in a Aden And Anais swaddle cloth covered in cartoon caterpillars. The designer blankets are sold in $50 four-packs.

The $$ letter

'Dear Max,' the 2234 word post reads. 'Your mother and I don't yet have the words to describe the hope you give us for the future. Your new life is full of promise, and we hope you will be happy and healthy so you can explore it fully. You've already given us a reason to reflect on the world we hope you live in.' 

The post did not reveal when little Max was born or her full name.  

The couple announced Priscilla's pregnancy on Facebook earlier this year - acknowledging their long struggle with fertility issues and revealing they had suffered several miscarriages before conceiving their healthy little girl.

They used the open letter as an opportunity to describe 'the world we hope she grows up in'. 

'Like all parents, we want you to grow up in a world better than ours today,' it says. 'While headlines often focus on what's wrong, in many ways the world is getting better. Health is improving. Poverty is shrinking. Knowledge is growing. People are connecting. Technological progress in every field means your life should be dramatically better than ours today.

'We will do our part to make this happen, not only because we love you, but also because we have a moral responsibility to all children in the next generation.

'We believe all lives have equal value, and that includes the many more people who will live in future generations than live today. Our society has an obligation to invest now to improve the lives of all those coming into this world, not just those already here.'

Later in the letter, the couple outline how they intend to make such a difference. 

'As you begin the next generation of the Chan Zuckerberg family, we also begin the Chan Zuckerberg Initiative to join people across the world to advance human potential and promote equality for all children in the next generation. Our initial areas of focus will be personalized learning, curing disease, connecting people and building strong communities.

99% of FB shares to be donated

'We will give 99% of our Facebook shares -- currently about $45 billion -- during our lives to advance this mission,' the letter says. 'We know this is a small contribution compared to all the resources and talents of those already working on these issues. But we want to do what we can, working alongside many others.

'We'll share more details in the coming months once we settle into our new family rhythm and return from our maternity and paternity leaves. We understand you'll have many questions about why and how we're doing this.' 

Facebook's Chief Operating Officer Sheryl Sandberg, wrote in response: 'This is a beautiful letter and an incredible commitment to future generations.'

Notoriously private Zuckerberg, 31, has been more public with the pregnancy and birth of his daughter than many would have previously expected. 

The CEO announced he would be taking two months paternity leave following Max's birth and outlined a new proposal to give Facebook fathers the option of four months leave on full pay. 

He said he made the 'personal decision' to take time off after reading studies that show 'when working parents take time to be with their newborns, outcomes are better for the children and families'. 

Back in August when  they announced they were expecting their first child they  also revealed they had suffered several heartbreaking miscarriages along the way. 

In a candid Facebook post, the couple detailed the heartache and loneliness they had experienced as a result.

'We want to share one experience to start. We've been trying to have a child for a couple of years and have had three miscarriages along the way.' 

'You feel so hopeful when you learn you're going to have a child. You start imagining who they'll become and dreaming of hopes for their future. You start making plans, and then they're gone. It's a lonely experience,' the couple said. 

'Most people don't discuss miscarriages because you worry your problems will distance you or reflect upon you, as if you're defective or did something to cause this. So you struggle on your own.

'In today's open and connected world, discussing these issues doesn't distance us; it brings us together. It creates understanding and tolerance, and it gives us hope.

'When we started talking to our friends, we realized how frequently this happened -- that many people we knew had similar issues and that nearly all had healthy children after all.

'We hope that sharing our experience will give more people the same hope we felt and will help more people feel comfortable sharing their stories as well.'

In Tuesday's letter Zuckerberg and Chan outline their plans to dedicate much of their new charity's work to health research. The move is unsurprising given Chan's training and work as a doctor in San Francisco and shows the foundation is a labor of love between the pair. The couple will also dedicate their fortune to education, 'promoting equality, connecting people and building strong communities'.

'Today we spend about 50 times more as a society treating people who are sick than we invest in research so you won't get sick in the first place,' the open letter explains. 

'Medicine has only been a real science for less than 100 years, and we've already seen complete cures for some diseases and good progress for others. As technology accelerates, we have a real shot at preventing, curing or managing all or most of the rest in the next 100 years.

'Today, most people die from five things -- heart disease, cancer, stroke, neurodegenerative and infectious diseases -- and we can make faster progress on these and other problems.

'Once we recognize that your generation and your children's generation may not have to suffer from disease, we collectively have a responsibility to tilt our investments a bit more towards the future to make this reality. Your mother and I want to do our part.

'Curing disease will take time. Over short periods of five or ten years, it may not seem like we're making much of a difference. But over the long term, seeds planted now will grow, and one day, you or your children will see what we can only imagine: a world without suffering from disease.'

The couple also revealed their dedication to San Francisco, pledging to begin their investment in education there before expanding it to the rest of the U.S.

Introducing the letter both Zuckerberg and Chan, 30, shared personal messages about the arrival of Max on their individual Facebook pages. 

Zuckerberg wrote: 'Priscilla and I are so happy to welcome our daughter Max into this world!

'For her birth, we wrote a letter to her about the world we hope she grows up in.'

'It's a world where our generation can advance human potential and promote equality -- by curing disease, personalizing learning, harnessing clean energy, connecting people, building strong communities, reducing poverty, providing equal rights and spreading understanding across nations.'

Chan wrote: 'I am beyond thrilled to introduce you to our Max. Her being fills us with hope and inspires us to join others in creating a better future.' 

Zuckerberg and Chan met at a party in Harvard in Zuckerberg's sophomore year and began dating in 2003. 

They married in his backyard in 2012 when Chan also celebrated her graduation from medical school. 

Tuesday's announcement was backed by a formal securities filing outlining that Zuckerberg would give away no more than $1 billion in Facebook holdings each year for the next three years. He also underlined his ongoing dedication to Facebook, retaining his majority voting position for 'the foreseeable future'. 

Though by far the biggest charitable pledge by the couple to date, they have been involved in many philanthropic endeavors since Zuckerberg first made his name and fortune. 

They have donated millions on work to improve education through the use of technology and earlier this week Zuckerberg was revealed as a signatory of the Breakthrough Energy Coalition founded by Bill Gates to coincide with the Paris climate change summit of world leaders.

The latest pledge puts the Zuckerbergs up there with America's most generous philanthropists alongside the likes of Bill and Melinda Gates who have given $30 billion to the work of their foundation and plan to continue donating their private wealth.