[Hemorrheological parameters during normal labor and uterine contraction]. / Paramètres hémorhéologiques pendant l'accouchement normal et la contraction utérine.

Considering the modified fluidity of blood during numerous kind of stress, the authors studied blood rheology during delivery as an example of a particularly severe stress. The authors measured blood and plasma viscosity and erythrocyte aggregation in 77 pregnant at the following stages of delivery: below 4 cm dilatation; more than 4 cm dilatation; during fetus expulsion, during after birth delivery. Apparent blood viscosity and viscosity adjusted to 45% hematocrit rose to reach a peak during expulsion (p less than 0.01) then to become normal again during placenta delivery (p less than 0.01). Hematocrit and plasmatic viscosity showed no changes during labour and expulsion. In addition erythrocyte aggregation was lowering during expulsion and delivery (stage with physiological defibrination). Rising blood viscosity might be explained by a red blood cell rigidification measured by the increasing of "Tk" (p less than 0.01) and by a nonsignificant increase of the filterability index measured by hemorheometer. In conclusion, delivery is accompanied by a blood hyperviscosity essentially related to a transient red blood cell rigidification.

[Hemorrheological characteristics of fetal blood drawn in utero from the cord]. / Caractéristiques hémorhéologiques du sang foetal prélevé in utero par cordocentèse.

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.