When you’re pregnant you’re encouraged to go to NCT classes to prepare for childbirth and becoming a parent. I propose an NCT-adjacent class, for the friends of pregnant people, to prepare them, too. I mean, it would be fun. I promise, we’d not make it not fun. There’d be crisps, for example. This manifesto-worthy idea came to me yesterday, as I sat glumly with myself and wondered why the idea of Peanut – the new Tinder-like app for finding other “mum friends” – brought with it a heavy feeling of personal doom.

It makes sense. The app makes total, solid definitely-can’t-fault-it sense. “I felt quite isolated,” the founder, Michelle Kennedy explained. “When it’s 2am and your baby has been up for an hour, there are very few people who understand how scary and lonely that can be, but a mama who is on Peanut at the same time, she gets it.” The free app matches mothers with similar interests – users can choose from “Fitness Fiend,” “Wine Time” and “Music is my Medicine”, which I am dying to take the piss out of but I won’t. Even though I’m dying to. I won’t.

There is no substitute for people who knew this new mother before her boobs came in, at her worst and her best

Because I get it, both the concept and the need. Three years on I’m yet to forget the sometimes howling loneliness of maternity leave, alone in the flat on a hot day except for this baby that is sometimes a wolf and sometimes a tiny glass menagerie. There were mornings I would wake from an hour’s unsleep filled with dread at a whole new day to fill with half-tasks and text messages. Having somebody to sit with while you wrestled your nipple into your new baby’s new mouth made a huge difference between feeling dead and alive. So yes, “mum friends”, these similarly harassed humans you are encouraged to seek out and eat cake with, to speed past all small talk with, to go straight from “Hello” to “Do you think you’ll ever have sex again?” with, are important.

But implicit in this theory is the understanding that your old friends – your non-mum friends – will, if not fade away, then become less important. Many women have told me how they felt when the rush of friends popping by to marvel at the child’s tiny fingers ceased, usually around two months in. Invitations died. The friends, they realised, assumed they wanted to be left alone. Or that they wouldn’t come out for a drink, because of the bother of leaving the house, what with the buggy, and all the stairs, and surely they’re a different person now, and won’t be interested in the idle gossip of their best friends, whose exes still message when drunk? And nobody tells them! Nobody tells the old friends, with their richly textured single lives, that “mum friends”, while lovely, are no substitute for people who have known this new mother since before her boobs came in, known her at her worst and best and during the awful “Jonathan years”.

Along with everything else you are expected to do as a new parent, women should not be required to make a whole new set of friends, or indeed to teach the old ones how to give a toss. Of course, it’s fantastic to welcome new people into your life, and in the sad twilight hours it’s important to feel you’re not alone. But there’s a babying here, I think – a sense that your old pals should not be bothered with the monotony, the infinite crushing love, the profundity of your new day-to-day; that it is too much for your old friends to know that you need them. It should not be the responsibility of the new mother to remind them she exists. Hence my proposal. As their friend’s due date approaches, a letter will arrive, inviting them to sign up for classes in empathy, memory, time-management, travel and humour. And then there’ll be a little illustration of some Pringles or whatever.

I find myself constantly, bullishly fighting with the idea that you are meant to become an entirely new person once you’ve had a child. This encompasses those messy debates about birth and breastfeeding, which assume you arrive here freshly hatched, without 30 years of anxiety, opinions and life behind you, a mother now, no longer a woman. The expectation that you will shrug off your old life, and with it the friends that populated it. Compared to the relationships you’ve built over years of biscuits and agony, the “mum friends” you click through on an app are worth, well, peanuts.

Email Eva at e.wiseman@observer.co.uk or follow her on Twitter @EvaWiseman