Heads in Malaysia have an unusual problem. Last year, the government asked them to draw up rotas for staff pregnancies. Two-thirds of its teachers are women and the irritatingly erratic arrival of their babies was giving ministers sleepless nights. To disrupt schools less, they said, they would prefer teachers to give birth during the holidays.

While nothing like that has happened - yet - over here, the age at which teachers have children, the length of maternity leave and what mothers do if and when they return to work are not just personal issues: they matter to heads, recruitment specialists and policy-makers.

British women are having children later - the average age for a first pregnancy in this country is 27 compared with 25 a decade ago. The number having babies between 35 and 45 has doubled in the past 20 years. Significantly, predictions from the Office for National Statistics suggest that a quarter of women born in 1972 will still be childless at the age of 45.

It is this last statistic that interests Professor John Howson of Oxford Brookes University. A man with his eye on the crystal ball of teacher recruitment, he worries that fear of infertility might scare women back to earlier child-bearing.

Teaching is an ageing profession that already faces a huge exodus over the next 15 years as today’s over-45s reach retirement age. Professor Howson is concerned about extra recruitment problems if there should also be “a structural shift” in the behaviour of the under-45s.

His concern is fuelled by Baby Hunger, a recent book by Sylvia Ann Hewlett which warns young professionals not to sacrifice their twenties and thirties to their jobs, only to realise later that they wanted to be carers as well as careerists.

Tina Richards (not her real name) can relate to the older women’s tales of regret in Hewlett’s book. Head of a Leicestershire primary, she is 42 and childless. “It’s not always easy meeting men when you work in the primary sector,” she says.“I didn’t meet my husband until I was 37 and you don’t just dive straight into making babies.”

Now she says it is too late. “If I had my time over again, perhaps I would have concentrated less on the job and more on making a life outside work. I would certainly advise younger teachers to get the work-life balance sorted out sooner.”

Philippa Nunn has just begun her balancing act. Since September, she has been head of The Holt, a beacon comprehensive for 1,200 girls in Wokingham, Berkshire. In January, at 36, she gave birth to Lara, her first child. Three and a half months later she was back at her desk.

“Ideally, I might have had children a little earlier, but you can’t plan these things so you get on with your life. I’ve spoken to lots of women who, like me, have just got their dream job and it suddenly happens - they’re pregnant.”

Mrs Nunn is perhaps a sign of the future: she is bucking the trend that has seen 85 per cent of secondary headships go to men. A survey in the late 1990s found that very few females under 40 in such posts, and more than half of those under 50, were childless.

Women might feel entitled to despair at the endless guilt-inducing debates about the ideal balance between work and children. The Baby Hunger generation blazed a trail into the boardroom for their sisters to follow. Today, they warn of a tug-of-love between diapers and directorships.

Before the Second World War, female teachers, like many public servants, had to resign when they got married. The swinging Sixties allowed them to hang on until they had children. It was not until the 1970s and Harold Wilson’s government that they were guaranteed their jobs back when they returned from maternity leave.

Teaching has traditionally been seen as a family-friendly job. Statistics released last year found that teachers and nurses born in the 1960s had babies later than colleagues born in the 1950s. However, they did not have them as late as women working in more male-dominated professions in which a child can be incompatible with climbing the career ladder.

This difference may be eroded by the long-hours culture prevalent in education. Primary teachers have had a particularly rough deal, says Professor Howson. He thinks that the workload crisis could tip the balance for a new mother deciding whether to return to school.

Flexible working and good affordable childcare are clearly important. The ONS longitudinal study compared French teachers and nurses with their British counterparts. It found that French women - with the advantage of more extensive government support for working mothers - were more likely to have babies younger.

The Government here has helped women indirectly by misreading teacher supply. The recruitment crisis has put women in a strong position when they ask for part-time work or job-shares, both of which are on the increase.

The state of the economy also affects child-rearing. A long period of low mortgage rates - and high pressure at work - means that, in some areas of the country, teachers can afford a house on one income, so mothers can afford the choice of taking a long career break.

Philippa Nunn knows of women taking time off to raise families, though often not out of choice. “There are teachers sitting at home looking after children who would work if the childcare was affordable and convenient,” she says.

She wants to open a day nursery at her school.“There are a number of staff who, like me, have young children, but wherever I go I don’t seem able to get any help. I don’t want subsidised day care, just help with the capital. But there are no grants, no avenues to money.”

Affordable childcare could make a huge difference in tempting quality staff to work at her school, which is in an expensive area, she says.

Sara Parsons, a 29-year-old science teacher at a private school in East Anglia, is expecting her first child in October. She and her husband would like to have four children so she is hoping for a part-time deal. Ms Parsons - her name has been changed to protect her negotiating position - is a woman who has her work-life balance sorted out.“I’d give up work tomorrow if I won the Lottery,” she says.