There is a striking moment in Sheryl Sandberg's loved and hated book Lean In, where the Facebook COO describes how, in an attempt to get home in time for her baby son's bedtime, she would hover in her then-employer Google's reception area at 5.30pm waiting until the car park was free of colleagues so she could hop into her car unobserved.
This is a woman at the top of her game, fully the holder of corporate power (and rising at 5am to check emails, then back on her laptop in the evening), but still embarrassed in case her colleagues thought she was slacking off.
It is important to acknowledge that not all women want or can have children, or are ambitious to reach the top of the largest agencies.
But what appears to have happened over the past few years is that increasing numbers of the potential female agency CEOs of tomorrow, the senior account directors on which agencies rely to keep clients happy and teams motivated, are deciding that the struggle to manage the demands of work and family are just too great.
A survey last year by recruiter Hanson Search found 48.5 per cent of women returning from maternity leave were considering leaving their job. In the words of one: "Flexible working is difficult in a client-facing environment. They don't work flexibly."
Social media mean that agency people often feel as if they are on 24-hour call, while those managing global clients can be answering emails from Asia over breakfast and taking calls from the US in the evening.
Add in the need to learn about financial management for anyone serious about running a business, and the strain starts to be keenly felt. In the words of a skinny young Ewan McGregor, these women are choosing life.
Many of the issues preventing women reaching the top tier are the same as in other sectors. But the fact that they apply in the PR world seems even more ridiculous: this is an industry that relies on people's ability to communicate - surely an ideal grounding for leaders.
And, even more galling, PR is full of women at the coal face. The last PRWeek/PRCA Census found that 65 per cent of PR professionals were female - look around you and that seems like an underestimate.
Women are well represented among the leadership of smaller and medium-sized agencies; 32 per cent of PRWeek's top 50 are led (or owned) by a woman.
However, many of these exist precisely because these women are choosing the kind of leadership role that allows them to combine work with family.
But taking your career in a direction that you hope will culminate in the leadership of a firm employing more than 200 people seems to be chosen by fewer and fewer PR women.
It is a situation that frustrates the women who have made it to the top of our largest PR agencies. Some seem ambivalent about talking publicly about their gender in relation to their job; others are bemused by the millennial generation taking a year's maternity leave when they settled for a few weeks.
All are eager to help women reach the top of the profession. There is also acknowledgement that this is an ambition that is demanding and not for everyone.
But the relative paucity of women in the top tiers of PR agencies cannot only be explained by work-life balance issues. For many, there is still a difficulty over how they feel about women in power.
This issue translates for some senior women into a difficulty in being authentic in their roles. "I feel that I have to hold myself back from being too emotional in case it just confirms my male colleagues' view that women aren't rational enough to lead," says one. "People seem to regard women in power as somehow unfeminine," says another.
This can lead to women feeling they must be apologetic about exerting their authority - or conversely, exerting it forcefully. The traditional hierarchies of big agencies can also alienate women, who are often happier working in a more collaborative way. And with so few women at the top, it is hard to find role models.
We will be exploring these issues over the coming months, notably with the introduction of a mentoring project to help women feel more able to reach the top levels of agency life.
Let us know your views in the comments below, or firstname.lastname@example.org
sallycosterton.blogspot.co.uk - Lively, illuminating blog by the former CEO of then Hill & Knowlton on everything from dealing with men grandstanding in meetings to the value of supportive partners.
leanin.org - The website for the foundation created by Sheryl Sandberg.
www.huffingtonpost.com/news/third-metric - Plenty of inspirational articles on work/life balance issues from the First Lady of female business leadership.
www.amazon.co.uk/The-Art-Managing-Professional-Services - One of the few books available about managing agencies
blog.ketchum.com/author/barrirafferty - The CEO of Ketchum’s US office blogs about female leadership issues