Pharmacokinetics of Low Molecular Weight and Unfractionated Heparin in Pregnancy

This study's specific objectives include: 1. Evaluating pharmacokinetic (concentration-time) and pharmacodynamic (concentration- effect) parameters for dalteparin and UFH prior to pregnancy, during the 1st, 2nd and 3rd trimesters and postpartum, using revised dosing protocols based on previous study. 2. Determining therapeutic response to the heparins, i.e. live birth rate and lack of maternal or fetal complications, in relation to drug exposure, based on AUC. 3. Documenting maternal and fetal complications during pregnancy for dalteparin and UFH, using the revised dosing protocols.