“Take a good, hard look at everyone in the room,” said the antenatal teacher. I looked: eight women, bloated beyond repair, tiny, anxious faces poking out above our distended bellies. All we had in common was a state of half-human, half-sow freakishness, able to crush our partners to death if we rolled off the bean bag by mistake.

“These people,” she went on, “will be your best friends for the rest of your life.”

Of all the scary things we were told in that overheated living room, this was the most unsettling. I had come to learn how to push the baby out – did this really mean I had to get rid of all my old friends too? But then it had never crossed my mind, before hearing her lectures, to massage my perineum; in contrast to that, the idea of spending the rest of my life as part of Sow-Freaks Anonymous wasn’t such a big ask.

In the event, like all that we were told, the teacher’s pronouncements were half-true. For five, isolated, desperate months, we were best friends. We clung to each other, as Rachel Cusk describes enviously of other babygroups in A Life’s Work, her memoir of new motherhood. “The babies cry and complain, but the women have lashed themselves together to form a raft of comradeship and they sail merrily over that which separately would have drowned them.”

I was unfaithful to everything about my old life, conducting instead an intense, all-consuming affair with multiple random women behind living room doors. After all, no one else shared our interest in “posseting” or Channel Five’s schedules during the graveyard shift the night before.

And then, just as suddenly, they were gone. Back to work, or the country, or simply whoever they were before. From meeting twice a week or more, there was nothing. We were over it. The whole babygroup experience had left me wondering about the nature of friendship: is it born of shared circumstance, and nothing more? And is the modern babygroup phenomenon, so cosy at first sight, really just another sign of our atomised age, itself encouraging further segregation?

To find out, I first went to northwest London, to visit a group of six couples who met in a National Childbirth Trust teacher’s garage, more than 18 years ago. They still remember walking into that room, in their Eighties maternity fashions: “That poodle hair, oh, and these baggy T-shirts with leggings…” says Tamar Italiaander, a medical secretary.

“Or denim dungarees!” exclaims Jill Farrell, now director of the Learning and Skills Council, and they all solemnly vow that once you have been pregnant in bad fashions, you’ll never wear them again, no matter how often they come back in.

They chat companionably, naturally settling into classic babygroup formation: partners at their side, sitting on sofas in the Italiaanders’ living room, as they have done in so many of each other’s living rooms. Except now, the offspring are not puking on the carpet, but traipsing to the door, hungover, talking about the 18th birthday party of another child of the group.

“We never thought we’d still be meeting now; we just thought we were going to learn a bit about having a baby,” says Tamar. It was only after the birth – what one man calls the “terrifying” days – when Jill recalls “feeling out of control,” with, as Gina Lane, now director of Lifelong Learning UK, says, “that feeling you get with a new baby, when you realise there is no on-off switch”, that they started to meet every week.

And they simply carried on, always, religiously, making a date for the next time before they parted. Fashions aside, now, “no one looks any different to us”, and they are almost perplexed to find themselves, in their mid-fifties, closer than ever, meeting a couple of times a year en masse, but some of the women speaking every day, “more like sisters than friends”. There follows some nervous laughter about the possibility that their children could now fall in love, do an NCT class, “and begin the life cycle all over again”.

“When you’re pregnant, you read avidly up to the point of childbirth, but not about toddler tantrums or puberty,” says Penny Clifton, a public relations director.

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