glycerine suppositories if it gets really bad. This is cure not prevention though... best ways to prevent it in the first place are trying to keep your stools SOFT - rather than eating loads of fibre to push out hard stools - you can end up with hemmorhoids and fissures that way, so be careful of too much fibre, especially if it is the processed (rivata, all-bran) kind.
Try to increase your intestinal flora by eating foods with probiotics in them, and also eating foods that the flora feed off, like bananas, onions, garlic, leeks
more here More flora = softer stools. Too much fibre = hard stools (its strips away flora, so overdoing it on the fibre can get you into a vicious circle)
Also, when you go to the loo, use a footstool so that you get into more of a squatting position, this means you have to push less, and empty your bowels more completely. If you dont have a footstool already, buy one for toddlers, it will come in handy for your bub eventually and wont look to weird in your bathroom.
If you are taking iron tablets, switch to slow release ones, and be very careful about taking cocodemol tablets - they will make constipation ten times worse.
If you currently eat a lot of fibre, and want to reduce it, you have to do it slowly because a sudden drop will make you very constipated (no flora present to soften stools, and no fibre to push them through) so if you currently eat a bowel of all-bran a day, start reducing slowly or replace with a more natural fibres (fruit and veg).
Better stop writing now, didnt realise I knew so much about poo and constipation