Just a child in a buggy passing by my mother in the supermarket used to be enough to make her weep openly.
Often, I would catch her looking at my daughter, Arwen, now three, with such a look of intense, desperate love that it took my breath away.
Mum was consumed by her longing for another child: a deep need to care for and cherish another little life.
Even after, aged 43, enduring a miscarriage, and then further years of fruitless trying, still, her desire for a baby remained undimmed.
In turn, her agony made me so sad. Mum and I had always been close, best friends as well as mother and daughter.
At 25, I’m the middle child, with Hannah, 27, and Harry, 22.
We had an idyllic childhood, growing up in Wales, despite the fact that our father was not involved in our upbringing.
Mum, though, was unerringly devoted to our every need, and worked hard in a care home. You might wonder why having we three children was not enough for Mum.
Well, aged 36, in 2006, she met Andrew, then, 33. It was a heady romance — within a month they were engaged, a year later they were married.
Andrew, who worked in the Forces, gave Mum a contentment I had never seen before. And she wanted to have a child with the man she loved so much.
Eventually, it became clear that she had few real options left — apart from one. Surrogacy, using another woman’s egg and Andrew’s sperm.
And there was only one person who would offer to help her with this. Me.
You may have taken a sudden intake of breath there — a daughter offering to be an egg donor and surrogate for her mother? What would this resulting baby be to me, you might wonder — a sister or a daughter?
For me, the answer has always been crystal clear. Any baby I would help my mother have would be my sister, and nothing more.
I am so convinced of this fact that I wanted to tell our story in full here today — before we have even told some members of our own family — to prove how a mother’s love need not be restricted by the confines of biology.
Two months ago, I gave birth to Willow, and handed her straight over to my ecstatic mum without a pang of doubt.
Lovely Willow may have been born using my eggs and Andrew’s sperm — but she has only one mother. And it’s certainly not me.
Our extraordinary story has been years in the making. Andrew and Mum longed for a child from the moment they married, but Mum had been sterilised after Harry was born, something she had long regretted.
Then, in 2014, Mum, then 43, plucked up the courage to have the procedure reversed, visiting a private clinic in Glasgow to do so. We live in Inverness.
The doctors also extracted and froze three of her eggs. As the reversal might not work, they explained, the eggs were an insurance policy meaning IVF could still be an option.
Just a few months later Mum conceived naturally — I was 19 at the time and I’ll never forget her elation as she told us — but then suffered a very early miscarriage.
It was devastating. For the next four years they continued trying, and watching her struggle was dreadful.
I would see the tears each month and understand what it meant. I felt powerless to take her pain away.
We became even closer in my early 20s. When I was 21, studying events co-ordination at college, and fell pregnant unexpectedly, it is the measure of her as a mother that she was instantly thrilled for me, despite her own longing for a baby.