For many women, the thought of their children heading into sixth form and off to university is the chance to reimagine life: the nest emptying, of course, but also a move away from motherhood and into a new phase; especially given that phase coincides with the probable arrival of the menopause.
But for me, those talks about the future with my teenage twin sons Harvey and Harrison and my husband Harry, the veteran Look North broadcaster, brought a rather different conclusion.
All I could think was: I'm not ready for motherhood to end yet. I'm not done. And then: I want to start again.
That was just over two years ago, at the end of 2017, and now I'm 20 weeks pregnant at the age of 51. I couldn't be happier.
Most of all, I want other women of my generation and age to know that, whatever you've been brought up to believe, motherhood doesn't have to end in our thirties. Our bodies are far more capable than we may have thought. And our choices should be wider.
I grew up, like many women born in the Sixties and Seventies, thinking that life should be centred on careers, jobs and climbing the ladder. And this I did very successfully.
I was a BBC TV news director working in high-pressured newsrooms. That meant being on duty for some of the most high-profile events of the era: the Dunblane murders and the death of Diana, Princess of Wales.
I felt I was working to my potential and a family was far from my mind. Wanting children was almost something to be ashamed of. High- fliers like me pushed it to one side.
Then, I met Harry - who was 17 years older than me - and we got married, moving back to York, the city where we had both grown up. At 35, I think children felt like something I ought to do - but I was already running out of time so, after consultations, we had IVF.
We were lucky. The first cycle produced our twins and although born premature by six weeks, they were healthy.
I loved being a mother from the off, but I wasn't done with being a working woman either. On maternity leave from the BBC in 2003, I realised I wanted a career change. I set up a Montessori nursery and then, over time, three more.
With a house full of boys and a workplace full of children, you might imagine that - of all women - I would be satisfied. And yet, and yet... there was a space that wanted to be filled.
When out walking our dogs, I remember meeting a woman who told me about her daughter leaving for university, and how grief stricken she felt. It really struck me. I started to think about what would happen after the boys, then aged 15, left - when there was no noise or mess.
I know not every woman feels like this. Some can't wait to reclaim their days. But there are plenty more, like me, who feel they must go along with what society says you should do at this point. Wave goodbye to your children, give into the menopause and buy another dog to meet your emotional needs.
I knew I didn't want that. At 49, I went for a run with Harry, then aged 66 and said: "I've been having these feelings I have to look into. I need to have another child. What do you think?"
And Harry, being the kindest man I know, looked at me and said: "We'd better get in touch with our consultant then."
When we spoke to him, a few weeks later, I was quite excited. "I think I can help you," he said. Then he added, "But, we wouldn't be able to use your eggs. They are too old and not viable."
I was taken aback. This went against all the messaging I had absorbed over the years - that you can have your career first and then your babies, because the technology would be there. Plus, I was still having regular periods; I had equated that with fertility.
Moreover, who hasn't seen the reports of celebrity women having babies into their fifties? Where did it say they used donor eggs? I had been sold the idea it was entirely possible.
So I had to think hard: did I want a mini-me or just to be a mother again? My decision was a quick one - motherhood was the thing that mattered. The boys were in the know right from the start. There were raised eyebrows to begin with, but then excitement kicked in. "You'd better get on with it," I was told. "We'll be leaving home soon and we want time to get know to know the baby before we do."
So, in January 2018, we began investigating our options. The first decision was to delay IVF until the boys' GCSEs were out of the way. I didn't want their schooling to be affected by me being pregnant; they didn't deserve that.
But we didn't have time to waste. The consultant recommended we use a clinic in Cyprus, as it can take months to find a suitable egg donor in the UK and regulations established by the Human Fertilisation and Embryology Authority do not permit treatment in women aged over 51 (the average age the menopause starts).
We chose a donor mother based on physical characteristics, academic history and interests such as sports - and in late January this year, we travelled there to have the IVF itself.
I had to prepare, taking hormones to support my womb, but I was in good shape for my age. I don't really drink alcohol and I run three or four times a week.
I spent about a fortnight wondering if I should have twins again, but our consultant put his foot down as soon as I mentioned it.
He pointed out that I just couldn't know what impact it would have on my body at my age. Not to mention that I had forgotten how hard it was last time, which to be fair, I had. We went ahead with the procedure, transferring one embryo and then all I could do was pray.
Twelve days later, at 5am, I took a pregnancy test. And there it was: positive. A relief, but I was well aware of everything that could go wrong. Thankfully, by having an egg donated by someone in their early twenties, we were able to ensure that the risks of a chromosomal disorder, such as Down's syndrome, were reduced. My eggs - had they fertilised at all - would have brought a much higher risk of this kind of issue.
Thanks to hormone therapy during the first weeks of pregnancy, I was at no extra risk of miscarriage - although I still worried, of course. And my age does mean I am more likely to suffer pre-eclampsia, which can cause premature birth, so I am being monitored for that.
But at 12 weeks, my scan showed a healthy baby: the right size for the date, moving, legs all over the place. That was the moment I really began to believe motherhood was going to happen again.
Harry and I have started to share our news. Reactions have been positive. "Why wouldn't you?" some have said. One or two women have confided they, too, wanted another child desperately - but didn't think it could happen.
I still can't quite believe my luck that Harry was happy to agree. If he had said no, I would have had to respect that. But I think he understood that to have stopped me would have been cruel.
Do I worry about the future? Not the parenting or sleepless nights (although we gave away the boys' cots long ago). I have confidence in my ability to cope. Nor do I worry about life expectancy. As much as I can, I will remain active, and healthy, and be functioning well enough to get this child into adulthood.
A family like ours has never been the norm anyway, thanks to the age gap between me and Harry, but our next child will have two older brothers who will also be role models. They are divided over wanting a sister; Harvey and I want to stick with boys, Harry and Harrison would prefer a girl. Either way, the baby's name will have to start with the letter H.
I'm sure there will be nerves closer to the due date in October, but my caesarean is booked. I have no regrets. And I hope I will inspire other older women to think once more about motherhood.
Why shouldn't science help women to have children when they want - just as men can? I am proof that anything is possible.
As told to Victoria Lambert.
The Sunday Telegraph