[Passage of commercial heparin and a low molecular weight fragment of heparin, CY 222, across the placenta of pregnant rabbits].

Because of a further clinical use of low-molecular weight heparin fraction in prevention or treatment of venous thrombo-embolism, it was necessary to establish whether they cross the placenta. The studies were performed in pregnant rabbits. High doses of commercial unfractionated heparin (1 000 and 1 600 anti-Xa units per kg of body-weight) and high doses of a low molecular weight heparin fraction (1 000; 8 000 and 16 000 anti-Xa units per kg of body weight) were injected to animals at the end of gestation (term: 30 days). The placenta crossing was studied by drawing blood samples from the mother and foetus for assays of heparin blood level. There is no detectable levels of heparin in the foetus at any time after injection of commercial heparin at the dose of 1 000 anti-Xa units per kg; meanwhile heparin blood level is very low at the dose of 16 000 anti-Xa units/kg. The low molecular weight heparin fraction do not cross the placenta at the dose of 1 000 anti-Xa units/kg. However for higher doses (8 000 and 16 000 anti-Xa/kg) this heparin fraction gives a foetal heparin blood level upper than the one given by commercial heparin.