i've taken elevit throughout both my pgs and not experienced any constipation.
constipation is a side effect of being pg not the suppls you take in my humble opinion, however I also eat LSA (linseed, sunflower & almond) everyday on my cereal or in a smoothie or salad (for variety so I don't get bored). Its got a slight nutty flavour and is good for you; its avail at any health food store .. I'd give this a go over metamucil or senakot personally!