Sarah Sands: It's better to be a young mum – and cheaper, too

The premise of Francis Wheen's new account of the Seventies, Strange Days Indeed, is that recent history can seem remarkably distant. It was pre- mobile phones, pre-Tony Blair and early Germaine Greer. Given the timescale, it is not surprising that we have lurched rather than marched towards social progress, particularly in the field of human relations.

The female turnout in senior jobs may be slightly less than the voting in the Afghanistan elections, but women have entered offices relatively recently and peacefully. A woman who joined the City in the Seventies tells me that she always assumed she would be the only woman in any meeting, and is just getting used to sharing glances and jokes with members of her own sex. So, if women are still refining the complexities of balancing work and home, one should remember it is uncharted territory.

New figures on population growth reveal a fascinating trend among women. Instead of delaying children in favour of careers, women are increasingly choosing to have children in their twenties, whatever the professional consequences.

Are women deciding to sod their careers and go for motherhood? Or, more hopefully, are women expecting higher levels of social responsibility from their employers?

Women who pursued careers in the Seventies were like first-generation immigrants: they kept their heads down and assumed very little. I came to Fleet Street in the mid-Eighties, but still accepted a long hours and booze culture swaggeringly at odds with family life.

Unusually among my contemporaries, I was married and knocked up by the age of 23, and so had to demonstrate my office worthiness. I pleaded for my first staff job after I was asked to guarantee that a baby would not interfere with professional obligations. I proved myself by showing up to work each day while my small son was in hospital with pneumonia. The greatest test of machismo for women of my generation was zero tolerance on maternity leave. Deals were sealed in the maternity ward. Those who returned to work with afterbirth in their handbags were applauded.

The enormous change in attitude was suddenly apparent at the start of this year when the 42-year-old French Minister of Justice, Rachida Dati, returned to work within five days of her child being born. Younger women did not admire Dati, they pitied her. And her deepest display of ambition was not even rewarded. Dati was cast out anyway by President Sarkozy.

Her plaintive case coincided with my own anecdotal observations of younger colleagues. They cannot understand the diffidence and muddle-headedness of the pioneering generations. They set out their stalls earlier and conduct relationships more decisively. They are better at biology and timekeeping. It makes sense to have children in your twenties rather than thirties and forties. If this means getting pregnant early in your career rather than later, why should that matter so much?

It is actually to the advantage of employers if women have their children on junior salaries, because it makes maternity leave cheaper. And just as young mothers have more energy and adapt more easily, so do young working mothers. Come to think of it, younger grandmothers would be sprightlier domestic support, too.

A generation of older mothers – cautious, tired and expensive – may turn out to be a historical quirk. In future, it will be the young women in offices who are confident enough to demand it all.