We are trailing around the Science Museum on a chilly February morning with an assortment of kids, all of them ours, most of them boys. "You don't mean that," I offer weakly, mesmerised by so much grey machinery.
"I do," Sophie protests with a hot, convincing rage. "I don't want to be around men just now. Not even Matt. They're so ... well, male." We both laugh at the inadequacy of this remark, and yet I know exactly what she means.
Sophie and I have always loved men but there is something about a brand new body taking root inside your own for nine whole months that makes you yearn for softer things.
I remember - some time towards the end of my last pregnancy - sitting in a Soho restaurant at lunchtime and suddenly being overwhelmed by the sight of all these dark suits and ties and tall, thick bodies. Blunt, powerful hands gripping wine glasses - alien creatures with hair on their faces, loud laughs, great jutting elbows.
It was too brutal for words. I wanted to leave at once and wrap myself in a duvet - inhale lavender oil, look at tiny, fragile things, talk to a girl.
The first time I saw Sophie, she was sitting on a dusty lino floor by a drinks machine in a grey pin-striped jacket she'd picked up in a thrift shop in South Carolina. The origination of the jacket seemed romantic beyond belief. She later gave it tome, but on my gangly frame it lost its glamour.
She had long, straight Annie Hall hair, greenish eyes, a wide, know-it- all mouth. I thought she was the bee's knees. The boy I was with that afternoon turned out to have been at school with the boy she was with. A loud reunion was going on over our heads. "This is dull," she said, snatching up her fraying denim bag, "Let's have tea."
It was love. We ditched the men and went back to her room and talked all night.
For three years, we shared flats, overdrafts, skipped lectures together. We ate cottage cheese and beetroot, took seaweed pills, argued about Descartes and Ayer, shared a copy of Vogue even when we couldn't pay the rent.
We might have shared men, too, had our styles not been so hopelessly different. I was the easy one, the bait, and men went for me first, but it was Sophie they took seriously. It was to Sophie they offered weekends away, balls, marriage - anything more interesting than sex.
I invested in Sophieness. I borrowed her perfume (Chanel No 19), her clothes (said pin-striped jacket), her figures of speech (various and always witty), but it didn't do the trick. I once asked her how many boys she'd kissed that term and she said none. My despairing answer was in double figures. She laughed and said my openness was part of my charm. Hers was that she always made me feel better.
The thing we did share was our "numbness" (our word) - a sense we had of being apart from everything and everyone, dislocated, unhappy. Sophie once woke up in floods of tears on her birthday. I took endless emotional risks because I wanted to feel something. We threw ourselves into our work, but poets and philosophers seemed to confirm what we already knew: that It Was All Hopeless. We were typical students.
"What am I doing here?" Sophie once blurted out to me as we breast-stroked up and down the Union pool. "I can't go on with this much longer."
Unlike me, Sophie got married properly, in ivory white. The night before her wedding, we walked up a hill in the wash of evening sun. The fields were fluorescent green, flattened by early autumnal wind. We came back in the dark. "It feels like it's happening to someone else," she remarked and I agreed.
Sophie and I have had our babies in relay, one after the other, our eldest only a month apart. These days the numbness is magically gone and we laugh when we recall our aimless, beetroot-eating selves.
Now we wander through a room full of Second World War fighter planes to the Museum Caf, where there are tiny, impossibly expensive squares of vanilla cake for the kids and cappuccino for us. The bigger children hanker for crisps and fizzy drinks andwe authoritatively refuse.
Sophie decants juice into a beaker with a lid. As she sits she automatically parts her legs around the bump. I realise I've forgotten how it feels to be more than just me.
A woman grins at her, leans forward: "Do you know what it is?"
"A baby, I hope," Soph snaps, with only just enough of a smile.
We spoon the froth off our coffee. "You don't really care what sex it is," I tell her.
"I do," she says. "Look at them." All our kids are in a single, writhing heap on the floor. Struggling limbs, puppy grunts, flashes of fist. "So much bloody testosterone."
We all drift and bump back through the museum, past the war machinery and the buttons to press and the beaten bronze panels and steel girders.
Sophie sighs again. Then she catches my eye and we both laugh.