remind me why i shouldn't lie on my back during pregnancy

[MrsRhettButler]

and when am i supposed to stop?
right now (28 weeks) i am most comfortable on my back but i seem to remember the midwife telling me not to when i was pg with dd but i cant remember why or at what stage... does anybody know?

there isnt really a hard and fast rule. you should just use your common sense, and do what is comfortable for you. Many womenfind it difficult because the weight of thebaby and placenta and uterus press down on the back, which is already being loosened by various hormones, so can result in back pain. but then, lieing on your front isnt really an option for some, and neither is your side. so, whichever way, you are basically stuffed. :S
just do what is comfortable.

The weight of baby and uterus presses on major bold vessels (aorta) restricting blood flow and can make you light headed.

You can't always control it. I used to wake up on my back.

Like Haunted says light headed/fainting and feeling sick as the blood from your legs and feet can't return to your heart. I was fine on my back until about 24 weeks and then just couldn't do it any more without it getting really painful. If you are comfortable though I say stay there, god knows there are enough other things to make you uncomfortable without adding to them yourself!

Agree with Joanne - its the inferior vena cava that gets crushed if you lie on your back and may make you light headed with numb arm and leg.....but, if you do lie on your back your body will prompt you to move believe me, even if you are in a deep sleep. Whilst you are able to, sleep in whatever position you find comfortable, sooner of later you are going to run out of any comfortable way to sleep and will be contemplating the possibility of sleeping standing up or sitting on your birthing ball!

It is advisable to sleep slightly tilted to your left side (just place a thin pillow under your back) because if you faint, due to low blood pressure caused by inferior vena cava compression, you will not be able to roll over.

Also, if a pregnant woman does faint, or feels faint, she should be helped to lie down on her left side, not her back, for this reason.

at sleeping on the birthing ball!
Thanks for the replys I knew there was a reason.
I do remember being more uncomfortable on my back by this time with dd which is why I was surprised that this time I feel much more comfortable on my back than any other position.
I would say I spend half the night on my left side and half on my back but wen I lay on the sofa its always on my back