[Hemorrheological characteristics of fetal blood drawn in utero from the cord]

Extensive studies of hemorheology of cord blood (drawn just after delivery) have evidentiated a peculiar rheological pattern: less filterable red cells, reduced erythrocyte aggregation, lowered plasma viscosity. This pattern has been suggested to be important for maintaining a sufficient O2 supply to fetal tissues, by avoiding hyperviscosity despite increased RBC rigidity. However, cord blood at birth is not exactly fetal blood and we are not yet aware of studies of fetal blood drawn in utero several weeks before delivery. For this reason, we investigated the rheological properties of fetal blood during intrauterine cord venepunctures in 27 pregnant women (25-30 week's gestation) who were explored for detection of fetal genetic or infectious diseases. Fetuses have lower plasma viscosity (p less than 0.001), lower RBC flexibility (measured by filterability on the Hémorhéomètre) (p less than 0.01) and higher hematocrit/viscosity ratio (p less than 0.01) than their mothers. While no temporal modification during the studied period (20-40 wk) was detected for hematocrit and plasma viscosity, RBC filterability (rigidity) seems to exhibit a 'U shaped curve' with a nadir between 25 and 30 weeks. This pilot study supports the hypothesis that the previously reported rheological properties of cord blood at birth reflect to some extent those of intra-uterine fetal blood.