There is a very simple explanation: the vena cava.

I treated pregnancy pretty much the same way I treat most activities: I read the instructions first. And several times during. Obsessively actually. Then I post-mortemed when it was over. The consequence of my PG by Numbers routine, which will no doubt get more thorough treatment on another occasion, is that I know what is going on here. Any pg book of any merit devotes at least 80 per cent of its contents to DON'Ts. And one of the big DON'Ts for a woman of your incubation is... tell me blossom, have you been sleeping on your back? Cos as all of us instruction-readers know, if you are pregnant and you sleep on your back you will be warned that the incubus will lie upon a significant vein (0r is it artery?), the vena cava. Most of the warnings describe the dire effect this has on your unborn child, but it always worried me that any cutting off of the circulation was surely more likely to hit Mum before bub. And again, I ask, sweetie, have you been sleeping on your back? And yes, I'm ignoring the kiddie porn of Topher Grace. See above. mtc Bec PS - I KNOW!!! I went through 18 pages of Google images and still couldn't find the pic I wanted. Kinda freaked out now. Thinking your hormonally advanced state is a bad influence. Guess I'll see if the Professor is still awake...