I've got very low iron levels (and due to give birth soon) and learnt that only about 15% of the iron in tablets are absorbed (at best) by the body. Many have more success with ferrous sulphate liquid.

I actually had an iron infusion today - it took about 5 hrs to do. I'll find out in 2 weeks after a blood test how successful it has been but given the tablets, liquid and lots of red meat (with vit C veggies etc) have done little for me i have great hopes for the infusion!