It's a funny old time, early pregnancy. You're not supposed to tell everyone why you are dragging yourself through the working day in a state of bone-vaporized exhaustion, why you are gagging at a colleague's innocuous air freshener, why you are irritably consuming mineral water at work social functions (I am ashamed to say I eventually snapped "I'm in rehab" to one innocent inquirer - sorry).

Exactly how and when to break the news to your boss and colleagues can be perplexing, particularly as the weeks wax and your waistline also waxes (although always having a cake on your desk can be a plausible if pathetic excuse).

Do you make an announcement after 12 weeks when the risk of miscarriage drops, or after the first scan, once strange movements are visible on the surface of your burgeoning "beer belly"? And what exactly do you say to your more macho male colleagues: "By the way lads, I'm up the duff. Mine's not a lager"?

For some women, especially those in predominantly male workplaces, there can be a terrible sense of exposure. The private life you've always kept private is suddenly pushing out the front of your suits. There is no male equivalent.

Julia, a 33-year-old former City of London high-flier, says: "It was weird. I spent 10 years in the City pretending not to be a girl and then you're pregnant and you can't pretend any more. You're at a meeting talking about something to do with business, and someone's kicking you from the inside. And how do you feel business-like in a tent dress and button-front tights?"

Julia's situation was made more difficult by the fact that she suffered from complications early in her pregnancy. "I had to go to the hospital for an emergency scan, so I ended up telling my boss and the team at around eight weeks.

"They were all terribly chivalrous at first. I got sent expensive flowers. They were all lovely about it - or so I thought."

Then Julia overheard the other members of her team on the phone, cutting her out of a deal. "The awful thing was the next day one of them was talking to me, saying how great it was about the babies and offering me all this old baby gear."

For other women, there are feelings of guilt - particularly for those who occupy an important position in a small company, or who know that her workmates are going to have to cover for her in her absence.

Because the reality is that, whatever the law says, maternity can still be perceived as a major inconvenience - to the company and to other colleagues. And women are still brought up to care about inconveniencing other people.

Anna, a marketing director for a design company, felt obliged to tell her (female) managing director when she was only seven weeks' pregnant because she'd just been given funds for a new project. Before she got the words out, her MD guessed.

"My MD said: `Don't tell me, you're f****** pregnant.' I replied: `This isn't quite how I was planning to tell you.' She turned to the chairman and said: `Don't worry about me. I've been sterilised.' I burst into tears."

Anna ultimately found herself "restructured" into a lesser role. She took voluntary redundancy and a modest payment, rather than fight it out in an employment tribunal a few months after the birth of her first baby.

Although most employers these days probably realise that it is unlawful to penalise a woman for having a baby, some are probably cynical enough to rely on the reluctance of many women to embark on litigation at a time which is supposed to be joyful (not to mention exhausting).

And ironically, the problems frequently arise with other women - the boss who feels her own plans for a baby are affected, the colleague who has fertility problems or has decided not to have children for career reasons and feels that women who do have children are somehow letting the side down.

And in a society where those with jobs increasingly seem to feel overworked, overstressed and sleep-deprived, there may also be a feeling that the woman who is taking maternity leave or coming back on flexitime is getting an unfair break or increasing the burden on others.

Imperfect as things are, we are none the less a world away from the experiences of our mothers' generation. Tessa was a social worker in the 1960s before the sex discrimination legislation was brought in. You didn't have to be pregnant to be written off at work, just being married would do.

"The first day I arrived at the office and sat in the duty room. The senior childcare officer introduced me as `Mrs'. There were a lot of unmarried women of a certain age.

"A lot was made of the fact that I got on well with the babies and children.

"Eventually, a senior childcare officer took me aside and asked if I thought I would be better off at home having some children of my own since I was clearly so fond of them.

"I was always treated as temporary. It was assumed that I would not stay. Young unmarried women who joined later were put on a promotion track and were treated differently."

Hopefully, many women these days find their experiences are similar to those of Nicola, who works in food technology for a major supermarket chain and whose employers seem to have done everything by the book.

Her pregnancy has made no difference to her internal job move and her boss encouraged her to work at her own pace and cut down on travelling when she began to have problems with her blood pressure.

Nicola finds that the pressure she feels comes from herself. She feels a sense of responsibility to her team, anxiety about how they will cope in her absence and unhappy that her health problems have meant that she cannot carry on exactly as normal: "You feel disappointed in yourself."

As for me, by the time I got round to telling my own colleagues, most of the women had noticed anyway. I like to think it was only because of the nose-dive my work wardrobe had taken - the sudden rash of gussets and smocking - but I'm probably fooling myself.

No doubt it was really the bad temper, the avocado complexion and the snoozing at the desk which gave the game away. But I needn't have felt any trepidation about coming clean, because everyone was charming. I was inundated by offers of advice, frocks, changing mats. Enough to moisten the eyes of an already fat and hormonal person.

And it was just as well I got it over with when I did, because the following week my belly did a weird trick, where it suddenly poked out dramatically like one of those poptop camper vans. Male colleagues shook their heads at it in bemusement: "I just can't believe I didn't notice that . . ."

Sheila O'Flanagan is on holidays.