Generation of a thrombin-like activity in late pregnancy

Evaluation of the haemostatic profile in the pre- and post parturient mare, with particular focus on the perinatal period

Various haemostatic analytes were systematically evaluated for four months pre-partum and five months post partum in 14 healthy mares. The plasma fibrinogen concentration and both Factor VIII:C and von Willebrand factor activity showed gradual increases from mid-gestation and reached maximal, or near maximal activity at parturition. These increases were paralleled by an increase in plasma fibronectin concentration, the appearance of fibrinogen degradation products, and a modest rise in antithrombin III concentration. In contrast, the activity of Factor VII and Factor IX, and the one-stage prothrombin (PT) time and the activated partial thromboplastin (APTT) time remained relatively constant throughout the pre- and post parturient period.

Thrombosis prophylaxis in pregnancy with use of subcutaneous heparin adjusted by monitoring heparin concentration in plasma

Twenty-six pregnant women were given prophylactic heparin treatment because of previous thromboembolic complications. The mean duration of treatment was 25 weeks (range, 6 to 32 weeks). The amount of heparin was adjusted to a plasma concentration of 0.08 to 0.15 IU/ml, measured as anti-factor Xa activity. This effect was compared with that on activated partial thromboplastin time. The average dose was 16,400 IU/24 hours or 225 IU/kg of body weight per 24 hours. When the plasma concentration was within the stipulated range, the dose was 234 IU/kg of body weight/24 hours. No significant prolongation of activated partial thromboplastin time was found in two thirds of the samples. Blood coagulation was either not activated or only slightly activated, as verified by a low level of fibrinopeptide A. Platelet counts and antithrombin III levels were generally not depressed. No thromboembolic complications occurred during the pregnancies or puerperium. Bleeding during delivery was not increased. No fractures of the spine caused by osteoporosis were found on radiologic examination post partum.

Fibrinopeptide A levels in maternal and newborn plasma

Plasma fibrinopeptide A (FPA), a dynamic measure of intravascular coagulation, was determined in 70 healthy Chinese women during normal pregnancy, labour, delivery and the early puerperium and compared to a group of healthy non-pregnant adult controls. In the normal controls the plasma FPA level (mean +/- SD) was 1.43 +/- 0.46 ng/ml. During pregnancy and labour, the FPA levels were 3.05 +/- 0.98 ng/ml and 11.47 +/- 4.43 ng/ml, respectively, and it reached a peak of 32.95 +/- 11.66 ng/ml at parturition, then falling to 6.15 +/- 2.52 ng/ml in the early puerperium. All these levels were significantly higher (p less than 0.001) compared to controls. Fifteen of the 21 mothers with blood sampling during parturition also had umbilical cord blood taken for determination of FPA level. There was no significant difference between the maternal (34.07 +/- 10.12 ng/ml) and cord (31.06 +/- 12.67 ng/ml) plasma FPA levels. It is concluded that the hypercoagulable state in women during pregnancy and the puerperium is associated with increased intravascular coagulation activity, and that increased intravascular coagulation activity also occurs in the fetus during parturition. This observation may account for the increased risk of thrombotic disorders observed in pregnant and parturient women as well as in the newborn.

Enhanced thrombin generation in normal and hypertensive pregnancy

We investigated the plasma levels of thrombin-antithrombin III complexes in women with uncomplicated pregnancy, patients with preeclampsia, gestational hypertension, and nonpregnant control subjects. In addition, we measured the coagulation inhibitors antithrombin III, protein C, and protein S. In normal pregnancy we observed a progressive increase in plasma thrombin-antithrombin III levels, and a decrease in protein S levels. In preeclampsia we observed increased thrombin-antithrombin III levels, reduced antithrombin III and protein C levels, and no further reduction of protein S compared with normal pregnancy. These new methods provide solid evidence for a prethrombotic state in normal pregnancy, especially in preeclampsia.

Quantitation of prothrombin activation products in human urine

Urine samples obtained from 37 normal individuals have been screened for the presence of prothrombin activation products using radioimmunoassays developed for fragment 1, fragment 2 and prothrombin derivatives bearing the thrombin region. The cross-reacting materials detected in urine were isolated by affinity chromatography on insolubilized antibodies, and analysed by SDS polyacrylamide gel electrophoresis. The only prothrombin derivatives detected were fragment 1 (37/37) and fragment 2 (22/37). The mean values of daily urinary fragment 1 and fragment 2 excretion were respectively 13.4 nM and 1.5 nM. The excretion of prothrombin derivatives has been quantitated in 14 normal pregnant women, during the third trimester of gestation. The mean values of urinary excretion were 47.2 nM per day for fragment 1 (P less than 0.005) and 6.4 nM per day for fragment 2 (P less than 0.05). The significant increase in fragment 1 and fragment 2 excretion observed in a condition known to be associated with the so-called hypercoagulable state suggest that the measurement of prothrombin derivatives in urine could be a useful tool for the non-invasive detection of thromboembolic diseases or prethrombotic states.

Antithrombin III in normal pregnancy

Plasma antithrombin III (AT III) was determined in 94 women during and after normal pregnancy employing an automated amidolytic technique. The patients were selected on the following criteria: no toxaemia, spontaneous delivery at term, birth-weight above the 10th percentile and discharged with a healthy baby. AT III levels during pregnancy and early puerperium were not lower than own control values obtained 6-8 weeks after delivery.

Fibrinogen turnover in pregnant rabbits during the first and last thirds of gestation

Although thrombin-mediated fibrinogen derivatives have been observed in normal pregnancy, an increased turnover of fibrinogen has been suspected but has not yet been demonstrated. Fibrinogen turnover was studied in 14 pregnant and 10 nonpregnant female rabbits by use of purified rabbit 125I-labeled fibrinogen. In the last third of gestation the half life of fibrinogen was shortened by 45% and the fractional catabolic rate increased by 44% in comparison to the values for the first third of gestation obtained in the same rabbits. The distribution volume of the injected fibrinogen representing the plasma volume increased by a mean of 18% during gestation. Fibrinogen concentration did not change during gestation. From a comparison of the measured data from the first and last thirds of gestation, it can be calculated that the synthesis rate of fibrinogen increased by about 80%. Furthermore, a positive correlation was found between the number of young per litter and the acceleration of fibrinogen elimination, indicating that a local process of intravascular coagulation in the placenta is responsible for the accelerated turnover of fibrinogen during gestation.