As compared to unfractionated heparin, low molecular weight heparins:

Unlike unfractionated heparin, LMW heparins have more consistent bioavailability as they get absorbed uniformly when given s.c. and thus do not require monitoring. Adverse effects of both types of heparins are similar. Both are contra-indicated in heparin-induced thrombocytopenia where the agent of choice is direct thrombin inhibitors like lepirudin.