Instead, Martin's yet-to-be-published book is called . It is an anthropological examination of the "rules, rituals, uniforms and migration patterns" of the super-rich mothers of London and New York, and it is surprising in two contradictory ways.

First, the ridiculous extremes we assume are apocryphal turn out to be true. Martin talks to me on the phone from The Hamptons, where the alpha species of Manhattan migrates in summer. I laugh at what she says, then, a second later, I have to check: "They don't actually do that, do they?" Despite being lauded in the media, this group's behaviour in private would mark them out as criminal or insane if they lived among us. Martin leaked the story of the scam used to get into Disney World earlier this summer and it was confirmed in an undercover TV investigation. A scandal ensued and Disney had to tighten its rules.

Second, the reality of these women's lives is the opposite of their media image. They are frenetic and worried, not idle and self-satisfied. They are so busy preserving their status that they can't enjoy it.

"The lives of these rich women I observed, whether on the Upper East Side or Notting Hill, are always portrayed as indolent. Instead I found women who are incredibly busy, with remarkably high levels of anxiety."

The third sociological point is that children are a marker of adult status as never before. Mothers feel stress because they deem themselves entirely responsible for the social and academic trajectory of their offspring, and that, in turn, is their method of social ascent in this hierarchical group.

"The status of one's child and your own reflects and builds on one another; it has become mutually defined," Martin says.

The Disney revelation was not the first time Martin had misgivings about the life she was living. She had a humble upbringing in the American Midwest, then went on to earn a PhD in social anthropology and taught at Yale University, but never felt she had found her calling in fieldwork. That is, until she married a Wall Street banker and felt forced to learn codes of behaviour that seemed more perplexing and morally uncomfortable than anything found in less manicured jungles.

"It was only when I had a child that I said to my husband, 'I'm feeling very strange, I think I have culture shock,'" Martin says.

When Martin was pregnant, a woman in a boutique implied she was a bad mother for not buying an expensive gadget to strap to her belly to supposedly give her baby a jump start in the literacy section of the school application process. Later, another mother mentioned she could hire a "playdate consultant" for US$400 an hour if her toddler was so overtaxed by academic consultants that he had forgotten how to play. Another parent engaged the services of a personal stylist to make sure she wore the correct attire to pick her child up from school. Martin realised she was not in Kansas any more.

Martin could not commit personally to this risible existence, so she committed professionally, becoming what anthropologists term a "participant-observer". The Western world has in the past decade become fascinated with the parenting of the super-rich. Not for nothing is actress Gwyneth Paltrow a perfect example of these mothers, a figure people love to hate: ludicrous and aspirational, derided and influential.

Despite all the attention, no one had analysed this world from the inside. Other fieldworkers may have had to eat termites and wear leaves to earn the trust of natives; Martin bravely had to drink almond milk lattes and buy Lanvin shoes.

"I never lost sight of the fact that this was a wholly foreign culture to me; my background is worlds apart from the world I married into. It was fieldwork."

Nearly three decades ago, in the book , a merciless portrait of exactly this class in 1980s Manhattan, Tom Wolfe coined the phrase "social X-ray" to describe ultra-rich women "so thin … you can see lamplight through their bones … encasing their scrawny shanks in metallic Lycra tubular tights for their sports training classes". The passage goes on: "To compensate for the concupiscence missing from their juiceless ribs and atrophied backsides, they turned to dress designers."

That much is still true. The most obvious marker of the tribe is women starved to extreme thinness by excluding major food groups and putting themselves through a series of punishing exercise regimens (ballet and boot camp are the disciplines du jour). For reference, see Paltrow, as above.

Martin managed to gain access to the most sought-after ballet exercise class in The Hamptons, where she saw the richest women in the world act like baboons in the African savannah. Scrawny millionaire mums duelled with their massive cars for parking places; once they secured entrance, "I saw arguments break out over territory, who gets what spot. If someone gets shut out of the class, there is often a big display of aggression."

Martin does allow herself a snigger at this point.

"What I saw in London and New York were punitive, gruelling exercise practices, almost like being tortured. That is an index of the lives of these extremely rich women, who literally hurt themselves. It's extreme in a way that going to an aerobics class is not."

Yet Wolfe in his novel goes to great lengths to describe what social X-rays are not: maternal. As he wrote in , there were no women on the 80s "Greed is good" scene who spoke of "hot food ready at six and stories read aloud at night and conversations while seated on the edge of the bed, just before the Sandman comes. In short, no one ever invited … Mother."

Martin's analysis shows how this has reversed. Decades on, the comparative women are like the mothers of dauphins, their ambitions realised through and with their child. For a mother to enter the most exclusive social circles, their child must get into the most exclusive schools. This requires Olympian displays of school fundraising, donations, coaching and lobbying.

"What's happened in the past 10 years is the fascination with rich, glamorous women's pregnancies and motherhood. The magazines that feature them are symptomatic of our fascination and build it at the same time. Most pregnant women feel bloated and unsexy; what these women present is a fantasy - that with enough money and commitment to the project you can still wear Christian Louboutin and Jimmy Choo, and be chic throughout childbearing.

"You can see why marketers love it, and for competitive women it creates a bar of excellence, a professionalisation of motherhood that allows them to feel successful if they achieve it."

Appearance, however, is a minor stress when compared with their progeny's development. Like primitive peoples, they don't have the same relationship to money as the rest of us, which is a problem in its own way. It is well documented that too much choice makes us anxious and these mothers suffer the consequences of an excessive array of consultants, tutoring and paid experiences for their child. It starts very early: Martin has even heard of a "crawling consultant" for a baby that was developing entirely normally, to give the infant a leg up. People are using specialists who were once employed to help disabled children on normal children - or perhaps you could say children who are disabled by wealth.

From then on it is all miserably competitive. Martin shadowed one London mother for a day, witnessing her sending 14 school-related e-mails, part of her determination to impress and to gain a good reference for the next school. Martin heard about a woman who bunged the director of a sought-after nursery a gift of a HK$60,000 Birkin bag. The driver was the fear of being excluded - which every tribal person knows is social death.

"There's a tacit understanding, sometimes explicit, that the more involved you are at your child's school, the better chance that the administration will speak well of you. These women don't stop talking about it in their sleep, they worry and work incessantly at it.

"It's nothing compared with not being able to feed your child or your child being sick and you not being able to pay for treatment, but one of the main features of their lives is anxiety. We have this big debate about what helicopter parenting is doing to children but what damage is this doing to the mothers?

"Because they have the resources to engineer better lives, they never stop. They have an infinite number of experts that they can hire to improve their family but it translates into greater stress and unhappiness."

She sounds so sympathetic I have to make the worst accusation that anyone can level at an anthropologist: has she gone native? At no point has she packed up her family and run screaming for her blissfully ordinary Midwest. Instead she has made small changes, such as moving her children out of the fastest lane of Manhattan's elite schooling; and laughing a lot more.

"Anthropologists always have these very vexed relationships with their native informants. Many times, yes, I would struggle with [thoughts of] going native …" Here she pauses, perhaps contemplating the sacrifices made by academics who bring up their children in their own rare tribes. "I wanted a Birkin bag very badly."

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FIRST-WORLD PROBLEMS

The parenting trap

"The women I've lived among and studied really don't fit the stereotype of the yummy mummy or The Real Housewives of New York City or the social X-ray. There is a fair amount of stress and anxiety that is very real and, to me, very touching, because it stems from wanting to be a good mother. Money in no way insulates these women from the fear of being a bad mother, or the fear of losing or failing their child/ren," she writes, via e-mail, from New York.

The project, which should result in a book in early 2015, focuses on the behaviour of mega-wealthy women in Manhattan and London but, says Martin, many of the pressures that make them act the way they do can be found elsewhere.

"One factor at play here is the stress of having little kids in a big city. It's hard to have a career or support your husband's career in an expensive, competitive city, while also being a perfect mother, and being fit, and being sexy, etc, etc, etc. And in big cities like Hong Kong, New York and London there are stressors like crowding, noise, traffic, pollution. These things make parenting stressful and difficult, even if you are rich."

According to Martin, the rise of China has brought with it a new predicament for the "tribe" she studies: "There is a new thing in Manhattan: the Asia Widow. That's my term for this newish Manhattan phenomenon - these women whose husbands go off to Asia or Southeast Asia for long periods of time. Sometimes they're gone for months at a time. Sometimes a woman's husband is in Hong Kong for half the year. She stays in Manhattan with her kids (and her staff). We have yet to see how these arrangements will affect marriages, women's independence and child development."

However, the unfortunate Asia Widow cannot win, because another set of problems awaits her if she moves overseas to be with her go-getting husband.

"We are adding to the mix cultural dislocation and women dispersing from their natal groups and kin networks, which worldwide is disempowering for women regardless of their material circumstances. The cultural dislocation can more difficult for non-working women with young kids than for their working husband. For example, they move to Hong Kong for his fabulous new job or promotion. He goes to work. She stays home with the kids. She is running a household in a new place where she does not likely have a lot of friends or support. If she has 'help' there may be vast cultural differences regarding how to run a home and how to interact with the kids. Little things like taking the kids to the park or the paediatrician are new and exponentially more difficult. He comes home at night to a wife who may be feeling overwhelmed, homesick, isolated. That's hard on a marriage."

And it is always him who is coming home in the evening to her. "My tribe is characterised by very traditional gender roles. With few exceptions she is the primary caregiver for the kids and he is the breadwinner."

Nevertheless, there are small differences between the tribes in the two cities she studies: "I noticed in London that the 'imaginary leash' - the amount of leeway parents and caregivers give kids to roam - is longer than it is in Manhattan. There's also more of a 'common sense' tradition of parenting in London, versus New York, where there is even greater dependence on experts."

But wherever these women live, there tends to be no escape from the pressures they pile upon themselves - even on holiday.

"In many instances it is hard for them to relax the need to always be on top, to always be winning. Vacations can be a form of conspicuous consumption, unfortunately.

"If any group could use downtime and real connection, it is the stressed and anxious parents of young children living in super cities."

 Mark Footer