"You're going to have to give up all that running," she said reproachfully, eyeing my not-yet-visible bump.
I stared at the floor and did a convincing impression of Hugh Grant struggling to stutter his way out of an awkward moment.
But why do we reserve such vitriol for expectant mums who exercise, when it's so widely documented that maintaining a fitness regime during pregnancy is beneficial for both mother and baby?
Professional fitness expert Hilary Burbidge says regular exercise, together with enough sleep and balanced nutrition are vital for both you and your growing baby. "Almost all exercises are safe for pregnant women with no medical problems, especially for the regular runner, cyclist, swimmer or free weights lifter – it's all totally fine, even into the later stages of your pregnancy," she says. "However, it's advisable to talk to your doctor before you start."
But not everyone agrees, as evidenced by mum of one Jenny Wright who hit the headlines last year when she wrote an article about her experience of being criticised by strangers, even called a selfish cow, for exercising while pregnant.
Jenny and her husband run a fitness company and offer courses in pre- and post-natal exercise. Jenny ran six or seven miles four times per week until she was about six months pregnant, switching to three or four miles for her last trimester. She ran until the day before she gave birth.
"During my pregnancy I didn't suffer from swollen ankles or loss of balance as many women do, and I didn't get stretch marks," Jenny says.
"I'm sure exercising all the way through pregnancy played a part in that, and I'm convinced that the physical stamina and mental toughness that you develop as a runner helped me cope with labour, too. Our daughter, Heidi, is absolutely perfect, and getting back into shape after pregnancy has been helped by the fact that I maintained my fitness throughout."
But Hilary adds that pregnancy is not the time to take up a high-impact sports programme that you've never done before, or begin training for a marathon. "Start with low-impact, gentle muscle toning exercises designed to help you stretch and become strong, like prenatal Pilates or yoga or even a brisk walk once a day," Hilary suggests.
"Whatever your level of fitness prior to being pregnant, listen to your body and be sensitive to how you feel. Being healthy, fit and in good shape will be an enormous help when you become a mother, and you'll get back into shape quicker too."
Mum of two Kate Gould continued running several times a week until she was six months pregnant with her first baby. Her midwife actively encouraged her to keep running. "She said I should continue to exercise as long as I felt comfortable, didn't get too hot and didn't feel dizzy," Kate recalls. "I had a fairly textbook pregnancy so felt able to continue running, although morning sickness prevented me from running much for the first 16 weeks but after that I kept going every week and loved it."
I'm not about to give up running just because I'm pregnant. Why? Mainly because the happy hormones that flow within the first few minutes of a run are sometimes the only thing left between me and the final shreds of my sanity after a difficult day.
I don't run because I'm addicted to exercise as I suspect some people assume. The speed with which I can find an excuse to ditch my run and stay home eating ice cream instead is proof of that.
And it's not about putting my body image ahead of the wellbeing of my baby, either. You only have to witness me limping breathlessly towards home to see that I'm no Paula Radcliffe and I probably won't feel like pounding the treadmill as my due date creeps into sight, but while running feels manageable I intend to stick with it.
Running clears my head unlike anything else, except perhaps a whole tub of ice cream. (Although that usually comes with a side order of regret and the need to undo the top button on my jeans, whereas I prefer the rosy glow and lean feeling that running leaves me with.)
And I've yet to encounter any problem that doesn't look infinitely less overwhelming after half an hour pounding along the beach with the waves crashing at your feet.
I'd run for those reasons alone, but when the ice cream compartment of the freezer starts calling my name it also pays to remember that studies have shown that women who exercise during pregnancy suffer less lower-back pain during pregnancy, have less need for pain relief during labour, and are less likely to suffer from post-natal depression.
And compared to women who don't exercise during pregnancy, we also gain less weight, have better mood and sleep patterns, and lose weight quicker after giving birth.
I don't say any of that to be smug - just to drive home the point that there's nothing vain or inconsiderate about refusing to let a bun in the oven put me off my stride when it comes to running.
Quite the reverse in fact. You could say I'm running for two.