Hemorrhage due to fibrinolysis in abruptio placentae

Hemorrhage due to fibrinolysis in abruptio placentae LOUISE LANG PHILLIPS, PH.D.* VALIJA SKRODELIS HOWARD C. TAYLOR, JR., M.D. New York, New York

A F I B R I N 0 G E N E M I A , as an obstetric complication, is widely recognized and since fibrinogen for intravenous administration is now available these cases are being handled in most institutions with a minimum of difficulty. Considerable disagreement persists, however, as to the mechanism causing this deficiency. While this question has been regarded as a matter primarily of academic interest, it may have more practical importance than has been realized. Thus, not only the optimum method of therapy but also the best time for administration of such therapy may well depend upon the etiology of this condition. Arguing from his theory of intravascular clottimr of fibrinrnren. Schneider has oostulated fuat adrninistr~tion of fibrinog~n in conditions such as abruptio placentae, longstanding fetal death, etc., may actually endanger the mother's life by increasing the total amount of fibrinogen available for conversion to fibrin and thus completely occluding blood vessels. 1 However, he admits that he knows of no such obstetric disasters

from the administration of fibrinogen. Indeed, it is surprising, if "intravascular coagulation" is the only process responsible for the phenomenon of hypofibrinogenemia, that a number of cases of rapid respiratory death, similar to that reported in cases of amniotic fluid embolism, have not occurred both in patients with severe afibrinogenemia and in those to whom large quantities of fibrinogen have been administered. On the contrary, most of the maternal deaths related to this phenomenon have been ones following uncontrollable hemorrhage in which a condition of afibrinogenemia has gone unrecognized or untreated for extensive periods of time until an apparently irreversible condition has been reached 2 • 3 or ones resulting from renal complications 1 to 2 weeks post partum. 2 • 4 The authors of this paper have suggested in previous reports5 • 6 that the most probable and perhaps essential condition for the development of extensive hemorrhage from hypofibrinogenemia lay in the activation of the fibrinolytic enzyme system. While this theory does not exclude the possibility of an initial intravascular coagulation, a :fibrinolytic process is probably of primary importance in the hemorrhage which accompanies this condition. This is a review of 24 cases of proved

From the Department of Obstetrics and Gynecology, Columbia Presbyterian Medical Center. This investigation was supported by Research Grant H-1512 from the National Heart Institute, National Institutes of Health, Public Health Service, Bethesda, Maryiand. *Recipient of Investigatorship under Contract I 145 from the Health Research Council of the City of New York.

hypofibrinogene...'llia in abruptio placentae

observed at the Sloane Hospital for Women, Columbia Presbyterian Medical Center, during the last 7 years. i44i

1448 Phillips, Skrodelis, and Taylor

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December I. 1962 Obst. & Gynec.

J.

Table I ---Type of delivery

Patient

Bleeding manifestations

Condition of infant

32

Cesarean section

Stillborn

40

''-~: .... _1

Stillborn

III

0 II II

33

Stillborn

Yes

E. C. V.D. L. J. A.M. E.M.

I VI IV VI IV

0 III III IV III

31 28 29 32 35

Manual dilatation of cervix Cesarean section Cesarean section Vaginal-oxytocin Cesarean section Cesarean section

Stillborn Neonatal death Stillborn Stillborn Stillborn

No No Yes Yes

C.]. H.L. L.R. A.S.

VIII III III II

VI I 0 I

31 21 25 32

Vaginal-oxytocin Vaginal-oxytocin Vaginal Cesarean section

Stillborn Stillborn Stillborn Neonatal death

? Yes

III

II IV I 0 I I I II 0 I 0 0

31 35 37

Vaginal Vaginal Vaginal Cesarean section Cesarean section Cesarean section Cesarean section Cesarean section Cesarean section Vaginal-oxytocin Cesarean section Vaginal

Stillborn Stillborn Stillborn Living and well Neonatal death Intrapartum death Neonatal death Living and well Living and well Stillborn Stillborn Stillborn

I 'V' • lt..K J.V~o

TTT

F. I.

Group B I. D. J. L. T.B. A.T. B. J. L. F. E. B. M.V. M.L. S.G.

P.H. B.S.

u~

v

III I II II II IV I II IV I

36 34

39 25 35 40

29 38 38

v

d5ll14l.1

Patient material During the period 1954 through 1960, 24 patients with premature separation of the placenta associated with fibrinogen levels below 200 mg. per cent have been studied at this institution. Since normal ranges during the third trimester of pregnancy are approximately 300 to 550 mg. per cent, levels below 200 mg. per cent represent at least a potential clotting hazard. Twelve of these patients received fibrinogen therapy, ranging in quantity from 2 to 6 Gm., and are designated Group A. Of these, 11 had fibrinogen levels below 50 mg. per cent and displayed acute hemorrhagic manifestations. The twelfth with a level of 126 mg. per cent and moderate vaginal bleeding was given 4 Gm. of fibrinogen preparatory to a cesarean section. The patients of Group B, in spite of low fibrinogen levels, did not show sufficient clinical signs of hemorrhagic difficulties to necessitate treatment with fibrinogen.

Yes

Ecchymoses Hematuria Ecchymoses

Oral Oral and pharyngeal Ecchymoses Oral

No No No No Yes Yes ? No

Methods Fibrinogen was determined by the method of Ratnoff and Menzie. 7 Free profibrinolysin was studied by tf!e hydrolysis of casein by plasma activated with streptokinase. The level as obtained by this method will depend directly upon the level of profibrinolysin but inversely upon the inhibitor level and therefore has little meaning alone. 8 Total profibrinolysin was obtained by the hydrolysis of casein by an isoelectric precipitate (from plasma) activated with streptokinase. When inhibitors are removed by this precipitation of the enzyme and the activity is determined in the redissolved precipitate a truer estimate of the profibrinolysin can be made than by studying the whole plasma. 8 Inhibitors (antifibrinolysin) are calculated from the difference between the total and free profibrinolysin. 8 Clot lysis was observed in serially diluted

Volume 84 Number 11, Part 1

plasma clots by a modification of Coon's method. 9 Other coagulation studies, such as prothrombin time/° Factor V, 11 prothrombin consumption time, ·• and thromboplastin generation times/ 3 have been carried out on some of these patients. Results

The obstetric data on both groups of patients are summarized in Table I. It is obvious that premature separation of the placenta can occur at any level of parity. Although it seems to have taken place earlier in gestation in the group showing severe hemorrhage, there is no statistical significance to the differences found between the two groups. Six cesarean sections were performed in Group A and 7 in Group B. However, no baby survived in the group requiring fibrinogen while 4 are living and well in the less severely affected group. In 5 of the 6 cesarean sections performed in Group A, Couvelaire uterus was found while 2 uteri of Group B were reported as ecchymotic. In Group A severe vaginal bleeding was reported in all cases either before or after delivery, and in many patients there were other hemorrhagic manifestations such as ecchymosis of arms and legs, hematuria, and oral or pharyngeal bleeding. In Group B vaginal bleeding was moderate to light and other symptoms of coagulation disorders were absent. All patients survived. The laboratory data and the quantities of blood and fibrinogen administered are presented in Table II. In each case the lowest fibrinogen level obtained is reported along with profibrinolysin and inhibitor levels found in that blood sample. The inhibitor levels are plotted against pints of blood transfused (Fig. 1) . Blood replacement is used here as a measure of degree of hemorrhage since the estimated blood loss is notably unreliable. The inhibitor level was in all cases based upon a blood sample drawn prior to replacement, thus ruling out a low level as a result of transfusion. Correlation coefficients were calculated for blood replacement as a func-

Hemorrhage due to fibrinolysis

1449

tion of inhibitor, total profibrinolysin, and fibrinogen levels. Correlations with significance levels of 0.004, 0.020, and 0.026, respectively, were found. Therefore, there is a significant negative correlation of the extent of hemorrhage with inhibitor level and a somewhat questionable negative correlation· with total profibrinolysin and fibrinogen values. When a comparison is made between Groups A and B, there are statistically significant differences ( P < 0.001) found in 'the inhibitor, profibrinolysin, and fibrinogen levels. It is to be emphasized that fibrinogen was administered simply on the basis of a clinical judgment that the hazard of a dangerous hemorrhage existed in a patient whose fibrinogen was below normal (200 mg. per cent). The absolute level of fibrinogen or other parameters while they may be indicative of the severity of the afibrinogenemia were not the deciding factors in any of the cases. Other factors of the coagulation system were determined in a few cases (Table III). Prothrombin times (fibrinogen frequently needs to be added to the plasma before determination) are usually elevated, probably because of partial destruction of both pro-

16~-------------------------------, 0

14

1Zto

"'::1 "' <

<)

..l

8

!:1t z

l___________________ 0---0----~ 0

0

0 0__ 0

.

0

0 0

I

INHIBlTOR

UNITS

Fig. 1. Correlation of inhibitor level in patients with premature separation of the placenta with blood required to replace that lost during parturition and puerperium.

Dee<,mber 1, 1962

1450 Phillips, Skrodelis, and Taylor

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J.

Obst. & Gynec.

Table II --~---·---

Replacement n

Fibrinogen Patient

(mg.

%)

L

r'

Free

(units)

I

Total

Inhibitors (units)

2.8 2.2 2.5 2.7 4.6 2.3 1.9 1.5 2.0

0.9 0.8 0.6 1.2 2.3 0.9 0.8 0.0 0.9

Clot lysis

Blood I (mi.)

Fibrin;~~~l(Gm.)

Group A

S.H. V.M. F. I. E. C. V.D. L. J. A.M. E.M. C.]. H.L.

L.R. A.S. Average S.D.

0 5 42 75 126 5 14 0 0 7 0 47

1.9 1.4 1.9 1.5 2.3 1.4 1.1

1.5 1.1

5+ 6+ 3+ 6+ 6+ 6+ 4+

26;7 4ll

1.57 0.15

2.28 1.20

0.9 0.6

Group B I. D.

68

77

0.7 3.1

1.3 3.3

94

2.1

2.8

5+

177

2.1 2.9 2.0 2.5 2.1 1.9 2.3

2.0 6.3 4.9 4.7 6.1 4.6 3.3 3.4 4.4 5.2

4+

J.L.

n r.r. .G.U::;J

A AA '"t',":t'J

"~~ &. • ..JJ

0.42 2.8 0.8-2.8

1.3 6.9 4.7-6.7

0.87 4.3 2.4-5.4

T.B. A.T. B.]. L. F. E. B.

M.V. M.L. S.G. P.H. B.S. Average

S.D. Term pregnancy Normal range

130 104 143 89 84 183 78

2.6 3.2 2.6 0.8 1.3 2.5 2.9

77 ' 'J e ll

46 393 200-400

thrombin and Factor V by fibrinolysin. 14 Plasma thromboplastin generation can be restored to normal by substitution of normal serum in the generation mixture but not by substitution of normal plasma. Factors of the fibrinolytic system found on serial studies of the first 3 cases presented are shown in Figs. 2, 3, and 4. While similar studies have been made on all patients, these are representative of the results ob· tained in severe hemorrhage following abruptio placentae. In each patient low levels of inhibitors and total profibrinolysin were found as well as low fibrinogen levels. Similar determinations on a patient (S. G. of Group B) with complete separation of the placenta without hemorrhagic manifestations

6+

5,000 2,500 7,500 3,000 1,500 1,500 1,500 2,000 3,500 2,000 2,500 2,000

4 4 6

3,100

4

2 4 6

4 4 6 0 ,)

3 2

1,500 500 1.000 1,500 1,000 500 3,500 1,500 1,000 500 1,000 2,500 1

n~:n

~,VJU

are shown in Fig. 5. Although the fibrinogen level fell from 280 to 180 mg. per cent in the 4 hours immediately following the onset of symptoms of abruptio placentae, the inhibitor and profibrinolysin levels remained essentially stable and within normal limits. Before delivery, 7 hours later, the fibrinogen level had returned to 270 mg. per cent. The results obtained on activation of the fibrinolytic system by streptokinase in a patient with lymphedema foHowing a radicai mastectomy are shown in Fig. 6. An initial injection of 100,000 units of streptokinase* was followed by a slow infusion of an additional 100,000 units. A blood sample was *Lederle's specially purified streptokinase.

Volume 84 Number 11, Part 1

Hemorrhage due to fibrinolysis

1451

Table III

Fibrinogen (mg. %)

Prothrombin time (seconds)

Factor V (%normal)

Patient

Time

E.M.

8:30 P.M. 10:05 P.M. 11:10 P.M. 1:00 A.M. 9:00A.M.

0 10 68 187

25 20 28 21 15

50 90 60 90 100

12:15 A.M.

14

25

15

L.J.

5

Thromboplastin generation ProClotting time (seconds)* thrombin consump- Incubation PPand NPand time tion time PS PS NS (seconds) (minutes)

28 38 41 18

2 4 6

8:15 A.M.

C.J. M. L.

108

19

131

20 16

30 70

3:00 P.M.

84

16

70

0

2 4 6

60

7:00P.M. 10:00 P.M.

2 4 6

*PP ::::: patient's plasma; PS ::::: patient's serum; NP

= normal

studied before injection, immediately after completion of the infusion, and 1, 2, and 5 days later. After administration of streptokinase to this patient, active fibrinolysin was demonstrated, the inhibitor and profibrinolysin levels \vere reduced to almost zero, and the fibrinogen level to 43 mg. per cent. The patient showed bleeding from the gums, from the site of a granulating wound, and from previous venepuncture sites. A large hematoma, the size of an orange, developed on her leg where she had bruised herself slightly earlier in the day. This patient clearly demonstrated the typical signs which are associated with hypofibrinogenemia accompanied by a fibrinolytic phenomenon. Furthermore, the low fibrinogen level refutes the impression held by many obstetricians that fibrinolysin cannot attack fibrinogen. Comment

Pritchard has shown evidence suggesting that 50 to 75 per cent of the fibrinogen lost from the bloodstream can be recovered in the retroplacental clot formed in abruptio placentae. 15 While his calculations do not take into account the probable synthesis of fibrinogen by the patient during the period

I :~

I

plasma; NS

~

27 20 23 17 18

22 30 35

16 15 17

20

16 17 19

normal serum.

between premature separation of the placenta and delivery, nevertheless, his figures show the deposition of a large quantity of fibrin. A mechanism for the return of red cells and serum to the maternal circulation as he proposes is somewhat more questionable. Injection of thromboplastin from a variety of tissue extracts can cause an intravascular deposition of fibrin with resulting reduction of plasma fibrinogen as has been shown by Page/ 6 Schneider, 17 and Stefanini. 18 However, there is no direct evidence that such an autoextraction of tissue thromboplastin and subsequent fibrin deposition does occur in abruptio placentae. Either of these two mechanisms might have contributed to the fibrinogen decreases in most of the patients in Group B where a low fibrinogen level but only moderate or light bleeding was observed, The values of profibrinolysin and inhibitors in this group while lower than those found in normal term pregnancies in most cases do not fall below the range expected in 99 per cent of normal nonpregnant subjects. Cesarean section could be performed on a number of members of this group without the severe hemorrhage encountered in Group A or in surgical pa·

1452

Phillips, Skrodelis, and Taylor

8

0

l;'i?-400 Ill)

s ci'

"

.sm ... Ill)

.c

~ 0

Fibrinogen

Fig. 2. Studies of the fibrinolytic enzyme system in Patient S. H. S. H. was admitted at 10: 30 A.M. with irregular abdominal pain following two falls as a result of dizziness at 3:30 P.M. Uterus was irritable and no fetal heart was heard. At 2: 30 A.M. patient suddenly lost 200 mi. of blood and blood pressure fell to 80/40. Fibrinogen was administered and bleeding gradually subsided. However, cervix was still undilated so cesarean section was performed at 10:30 A.M.; 2,000 mi. of blood and clots were found in the uterus and an additional 700 mi. was lost during the procedure. Postoperative bleeding was minimal.

December I, 1'162 Am. j. Oh
tients with a fibrinolytic problem. On the basis of Pritchard's report, 15 • 19 many of his cases would apparently fall into Group B. A third mechanism for the reduction of fibrinogen is the hydrolytic destruction by an active fibrinolysin. Extreme derangements in the fibrinolytic system are evident in the group manifesting difficult hemorrhagic problems. In this group the degree of hypofibrinogenemia (if it already exists) is accentuated by enzymatic hydrolysis of fibrinogen. In addition, the weak clots formed under these adverse conditions are subject to lysis by the same fibrinolytic enzyme. The implication of such a process is clearly shown in a number of aspects of the data presented here. 1. Fibrinogen depletion can occur as a result of activation of the fibrinolytic system, in vivo (Fig. 6). The fibrinogen, profibrinolysin, and inhibitor levels were all found to be extremely low following infusion of streptokinase, a known activator of the endogenous profibrinolysin. The changes resulting from streptokinase infusion are essentially the same as those found in 3 patients, whose findings are shown in Figs. 2, 3, and 4 where hypofibrinogenemia followed premature separation of the placenta. 2. Highly significant differences with respect to antifibrinolysin and profibrinolysin were found between the two groups of patients. The levels of the group manifesting bleeding of sufficient degree to necessitate administration of fibrinogen were extremely low. The deficient inhibitor level probably permits activation of the profibrinolysin while the decreased profibrinolysin level is an indication that the fibrinolysin precursor has been changed into its active form. 3. A close negative correlation of the antifibrinolysin with the amount of blood required to replace that lost by the patient during parturition and the postpartum period was found. This is again evidence of the influence of the fibrinolytic system on the degree of hemorrhage encountered. 4. Factor V, plasma thromboplastin component, and/or Stuart factor are the principal coagulation requirements other than

Volume 84 Number 11 , Part 1

Hemorrhage due to fibrinolysis 1453

........,"'

§

~

'§

..:-

"0

.0

.~

j

4

0 .<;:::

:.a

.a z

2

Fibrinogen

blood

Fig. 3. Studies of the fibrinolytic enzyme system in Patient V. M. V. M. was admitted at 8:15 with abdominal pain of 9 hours' duration, tense uterus, and no fetal heart tones. Membranes were ruptured artificially. Vaginal bleeding was slight but a catheterized urine specimen was grossly bloody. Therefore 4 Gm. of fibrinogen was administered. At 1:45 P.M. patient delivered a stillborn infant. The placenta followed immediately with 1,500 ml. of ciotted and 1,000 mi. of fluid blood. Fresh blood as well as stored bank blood was given to replace that lost. A.M.

fibrinogen which are found to be decreased in severe abruptio placentae (Table III). These are substances which would not be significantly altered in a process of coagulation but could be by a fibrinolytic process. On the other hand, antihemophilic factor which would be removed by a coagulation mechanism is apparently unaffected in the

Fibrinogen Fig. 4. Studies of the fibrinolytic enzyme system in Patient F. I. F. I. was admitted at 7 P.M. with intense abdominal pain of 3 hours' duration and profuse vaginal bleeding. Membranes were ruptured artificially, the cervix was dilated manually, and a stillborn infant was delivered at 7:50 P.M. At 10 P.M. the patient began to bleed severely and blood pressure dropped to 60/40. Exploration of the uterus revealed a rent in the lower uterine segment so a. total abdominal hysterectomy was performed while fibrinogen was being administered. Postoperatively the patient continued to bleed until a pint of freshly drawn blood was given at 5:30 A.M. This resulted in marked improvement in her condition.

December 1, 1962

1454 Phillips, Skrodelis, and Taylor

Am.

patient whose thromboplastin generation was studied. 5. Clot lysis and euglobulin lysis were seen more frequently in Group A (fibrinogen) than in Group B (no fibrinogen). However, failure to demonstrate increased lysis in some cases does not constitute proof that activation of the enzyme has not occurred. Fibrinolysin is a labile enzyme and

J. Obst. & Gynee.

6~--------------------~ 4

2

8

0


6400 Q-

""" 0

·~

!m

.0

~

Pre Rls: SK SK am

am

am

am am

n

Fig. 5. Studies of the fibrinolytic enzyme system in Patient S. G. S. G. was admitted at 1:30 A.M. with typical symptoms of abruptio placentae but minimal bleeding. Fibrinogen and fibrinolysin studies were followed at 2 hour intervals until she was delivered uneventfully 10 hours later.

2 Days

5

200, oco units

Fig. 6. Studies of the fibrinolytic enzyme system in a Patient followinl! infusion of streptokinase. R. R. is a patient with lymphedema following a radical mastectomy to whom streptokinase was administered in order to activate the fibrinolytic system.

Volume 84 Number 11, Part 1

its detection may depend upon the time the blood sample is drawn in relation to placental separation. Lysis is more apt to be observed early in the process before minimum fibrinogen levels are reached. Treatment

The results presented here emphasize the importance of good clinical judgment as well as a laboratory determination of fibrinogen level. Intravenous fibrinogen should not be given merely because a low level has been demonstrated, but when hemorrhage has become a problem or is anticipated during a surgical procedure. On the other hand, fibrinogen should not be administered for bleeding unless a depressed level has been proved. Where a quantitative determination is not obtainable the Reid "whole blood clot observation" still seems to be the most useful and reliable of the easy methods. 20 If fibrinogen is administered a minimum of 4 Gm. is probably desirable. This amount should raise the plasma level by approximately 100 mg. per cent. However, if an extremely active fibrinolysis persists, larger quantities may be required and administration should be continued as needed. The question is frequently raised as to whether fibrinogen may safely be given before the delivery of the fetus. It was administered to patients S. H. and V. M. 8 and 4 hours, respectively, before delivery. This resulted in control of bleeding problems and permitted deliveries to be made under optimal conditions without any evidence of harmful effects from its administration. Concomitant transfusion of fresh blood as opposed to stored bank blood may help in restoration of labile coagulation factors such

REFERENCES

1. Schneider, C.: Ann. New York Acad. Sc. 75: 634, 1959. 2. Dyer, 1., and McCaughey, E. V.: AM. J. 0BST. & GYNEC. 77: 1176, 1958. 3. Heaton, S. C., Solomon, C., and Happel, E.: AM. J. 0BST. & GYNEC. 70: 320, 1955. 4. Tuller, M. A.: AM. J. 0BST. & GvNEC. 73: 273, 1956.

Hemorrhage due to fibrinolysis

1455

as platelets and Factor V. Patient F. I. is an excellent example of the necessity for such treatment where response to adequate fibrinogen therapy is poor. In order to minimize the risk of homologous serum jaundice all of the fibrinogen administered to a patient should come from a single lot number. Of the 12 cases who received fibrinogen in this series one patient developed a mild case of jaundice 4 months following delivery. Where bleeding is moderate, administration of estrogens intravenous has been shown to raise the fibrinogen level from 50 to 100 mg. per cent in a number of patients with a mild degree of hypofibrinogenemia. 21 This increase, which does not occur when fibrinogen levels are normal may be due either to inhibition of fibrinolysin or to increased synthesis or mobilization of fibrinogen stores. e-aminocaproic acid has been used as an efficient inhibitor of fibrinolysin activator. However, at the present time its use should probably be reserved for extremely refractory cases, since subendocardial hemorrhages have been reported in animals following slow and prolonged infusion. Rapid injection in large quantities apparently does not produce this lesion. 22 Summary

Significant differences between the determinations made on the 12 patients requiring fibrinogen and the 12 not requiring it, with respect to the behavior of antifibrinolysin and profibrinolysin were noted. The data support the theory that active fibrinolysin plays a decisive role in the intractable bleeding seen in patients with abruptio placentae.

5. Phillips, L. L.: Ann. New York Acad. Sc. 75: 676, 1959. 6. Phillips, L. L., Montgomery, G., Jr., and Taylor, H. C., Jr.: AM. J. 0BsT. & GYNEC. 73: 431, 1957. 7. Ratnoff, 0. D., and Menzie, C.: J. Lab. & Clin. Med. 37: 316, 1951. 8. Phillips, L. L., and Skrodelis, V.: J. Clin. Invest. 37: 965, 1958.

1456 Phillips, Skrodelis, and Taylor

9. Coon, W. W., and Hodgson, P. E.: Surg. Gynec. & Obst. 95: 717, 195 2. 10. Quick, A. J.: The Physiology and Pathology of Hemostasis, Philadelphia, 1951, Lea & Febiger. 11. Stefanini, M.: Am. J. C!in_ Path. 20: 233, 1950. 12. Sussman, L. N., Cohen, I. B., and Gittler, R.: J. A. M. A. 156: 702, 1954. 13. Duckert, F., Fluckiger, P., Isenschmid, H., Matter, M., Voleg-Meng, J., and Koller, F.: Acta haemat. 12: 197, 1954. 14. Soulier, J. P., Alagille, D., and Larrieu, M. J.: Semaine hOp. Paris 32: 359, 1956. 15. Pritchard, J. A., and Wright, M. R.: New England J. Med. 261: 218, 1959.

December I. Am.

196~

J. Obst, & Gyncc.

16. Page, E. W., Fulton, L. D., and Glendening, M. B.: AM. J. 0BST. & GYNEC. 61: 1116, 1951. 17. Schneider, C.: Am. J. Physiol. 149: 123, 1947. 18. Stefanini, M., and Turpini, R. A.: Ann. New York Acad. Sc. 75: 601, 1959. 19. Pritchard, J. A.: AM. J. 0BsT. & GvNEC. 76: 347, 1958. 20. Weiner, A. E., Reid, D. E., and Roby, C. C.: AM. J. OBsT. & GYNEC. 66: 474, 1953. 21. Phillips, L. L., Turksoy, N., and Southam, A. L.: AM. J. 0BST. & GYNEC. 82: 1216, 1961. 22. Guzman, R.: Special report to Cutter Laboratories.