- Email: [email protected]
Creatinine, uric acid, and electrolytes in amniotic fluid
volume
106 number 3 I, 1970
February
hetican
Journal
of Obstetrics and Gynecology Transactions Annual
of
Meeting
Obstetricians
the
Twenty-fifth
of the
Society
and
of
Gynaecologists
of Canada
Creatinine, uric acid, and electrolytes
in amniotic
fluid T.
A.
S.
BJERRE,
DORAN,
C.
J.
PORTER,
Toronto,
Ontario
M.D. M.Sc. PH.D.
Four hundred samples of amniotic fluid obtained by amniocentesis, mostly from Rh-sensitized patients, were analyzed for creatinine, uric acid, sodium, potassium, and chloride. Amniotic fluid creatinine values were below 1 mg. per 100 ml. before 28 weeks and about 2 mg. per 100 ml. close to term. Eighty-six per cent of all creatinine values at 37 weeks’ gestation or more were at or aboue 1.6 mg. per 100 ml. Serial creatinine values in stillbirths were generally low and showed a decline. There was good correlation between creatinine values and both birth weight and maturity of infants born within one week of amniocentesis. Amniotic fluid uric acid increased with gestational age with a fairly wide scatter. Values for sodium and chloride stayed approximately in the range of those for normal serum with a slight progressive fall to term. Potassium values stayed within normal serum values but showed a slight rise to term. Amniotic fluid creatinine showed the most definite trend with gestational age and thus is a useful test for fetal maturity.
S I N c E Bevisl in 1950 described the use of amniocentesis to study bile pigments in amniotic fluid, it has become an increasingly useful technique in the assessment of the
Rh-isoimmunized patient.2p 3l 4 More recently, other substances in amniotic fluid have been studied61 6* T and there has been an interest in the use of amniocentesis in the assessment of fetal maturity. Amniotic fluid has been examined for maturity both cytologically and biochemically. Mandelbaum* demonstrated a progressive fall in amniotic fluid bilirubin in normal pregnancy where no Rh sensitization occurred. He has suggested that the absence of the 450 p peak is
From the Departments of Obstetrics and Gynaecology and Biochemistry, Toronto General Hospital. Presented at the Twenty-fifth Annual Meeting of the Society of Obstetricians and Gynecologists of Canada, Toronto, Ontario, ]une 13-15, 1969.
325
326
Doran,
Bjerre,
and
Porter
indicative of fetal maturity greater than 36 weeks. Brosens and Gordon9 and Bishop and CorsonlO have demonstrated an increasing percentage of fat cells of fetal sebaceous origin in the amniotic fluid with maturity and suggest that this is a good test for fetal maturity. Pitkin and Zwirekll studied amniotic fluid creatinine obtained by amniocentesis in 120 patients. Forty-seven of these patients had medical comphcations and 73 had uncomplicated pregnancies. They found that the level of amniotic fluid creatinine remained constant or increased very little to 34 weeks, when an abrupt rise took place so that after 37 weeks the level was 2 mg. per 100 ml. or higher in 94 per cent of patients. They felt that this assay could be a useful test of fetal maturity. CherryI” measured amniotic fluid creatinine to maternal serum creatinine ratio in 60 patients, 22 of whom were diabetic. He found an increasing content of creatinine in amniotic fluid with gestational age and a decreased ratio of amniotic fluid creatinine to maternal serum creatinine in diabetes. Over the past 4 years we have utilized amniocentesis in our hospital on almost all Rh-sensitized patients and in addition, have provided a spectrophotometric analysis service on amniotic fluid samples sent in from four other hospitals in our area. A small number of control samples of amniotic fluids from therapeutic abortion specimens were collected. In addition to measuring amniotic fluid bilirubin on these samples,13 we have measured creatinine, uric acid, and electrolytes as well as some enzymes not covered in this paper. I* Our purpose here is to report on our findings with particular emphasis on the measurement of amniotic fluid creatinine and its relationship to maturity. Unquestionably, situations arise in obstetrics where intervention is contemplated and where a reliable test for fetal maturity would be invaluable. Materials
and
methods
Four hundred and twenty-six amniotic fluids by amniocentesis were studied. For technical reasons it was not possible to do multiple biochemical determinations on all
Amer.
February J. Obstet.
1, 1970 Gynec.
the amniotic fluids obtained. There were 119 single amniocenteses and 307, serial ranging from 2 to 6 amniocenteses in the same patient. Three hundred and sixty-nine amniotic fluid samples were measured for creatinine. These samples were grouped as follows : Controls 8 Unaffected 57 Mildly affected 66 Moderately affected 133 Severely affected 49 Stillbirths 56 Controls, unaffected and mildly affected were grouped as “normal” and moderately affected, severely affected, and stillbirths as “abnormal.” The fluid was centrifuged, filtered and creatinine content was measured by a modification of the Jaf?‘C picric acid method.15 -4mniotic fluid uric acid was measured in 253 samples by the method of Browne and Freier.16 Sodium, potassium, and chloride were measured simultaneously in 333 samples by the AutoAnalyzer method.17 Results
Creatinine. Fig. 1 summarizes results obtained for creatinine levels in all amniotic fluid samples. Although there was a smaller number of samples up to 24 weeks’ gestation, levels seemed to remain constant during this period. There was a gradual increase from 24 to 34 weeks’ gestation, then a more abrupt increase from 34 weeks to term. Creatinine values were generally below 1 mg. per 100 ml. at less than 28 weeks and were at about 2 mg. per 100 ml. near term. Eighty-six per cent of all creatinine values at 37 weeks’ gestation or more were at or above 1.6 mg. per 100 ml. at 37 weeks’ gestation or more were at or above 1.6 mg. per 100 ml. In an effort to reduce the effect of Rh sensitization, mean values for the “normal” and “abnormal” groups were calculated and plotted at two weekly intervals (Fig. 2). The stippled area represents two standard deviations from the normal mean values. The mean values for the “abnormal” group were slightly lower than the “normal” group throughout
Volume Number
Contents
106 3
4.0
F
3.2
0
SlILlBIRTHS
.
SEVERELY AFFECTLO
I
MOD, UNAFFECTED AND CONTROtS
of
amniotic
fluid
327
WEEKS OF GESTATION Fig.
1. Amniotic
2.8
fluid
creatinine
levels-all
samples.
•“N~RMAL”MEAN
VALUES
b”ABNORMAL”MEAN
2.4
-
2.0
-
1.6
-
1.2
-
.a
-
VALUES
5 8 7 : ii i F z 25
.4
x
t t
12
I
i
16
I
20
I
I
24 WEEKS Of
‘Fig. 2. “Normal” and represents two standard
“abnormal” deviations
amniotic fluid from the “normal”
I
1
I
28
1
1
1
32
36
40
QESTATION creatinine mean mean values.
values.
The
stippled
area
328
Doran,
Bjerre,
and
Porter Amer.
Table
I. Mean
values for amniotic 13-29% No.
fluid
creatinine,
uric 30-34%
weeks Mean
No.
February J. Obstet.
1, 1970 Gynec.
acid, electrolytes weeks
Above
Mean
No.
35 1
weeks Mean
31
0.97
53
1.40
47
1.88
76
0.87
104
1.24
58
1.65
Normal Uric Acid Abnormal
22
5.09
33
6.05
26
6.42
57
4.92
73
5.81
37
6.74
Normal Sodium Abnormal
27
136.74
45
134.58
39
132.89
70
140.18
95
136.55
51
132.80
Normal Chloride Abnormal
27
112.70
45
111.62
39
111.05
70
115.06
96
112.66
51
110.59
27
4.01
45
4.30
39
4.54
69
4.10
96
4.24
51
4.57
Normal
Creatinine Abnormal
Normal Potassium Abnormal
pregnancy, the difference increasing after 32 weeks’ gestation. The “normal” mean value for creatinine from 36 weeks to term was 1.9 mg. per 100 ml. and the “abnormal” mean in the same gestational period was 1.8 mg. per 100 ml. Amniotic fluid creatinine values for stillbirths were generally low and serial values tended to show a decline (Fig. 1) . Mean values for three gestational periods for “normals” and “abnormals” are shown in Table I. As illustrated in Fig. 2 there was a small progressive difference between “normal” and “abnormal” mean creatinine levels in each gestational age bracket. To illustrate creatinine trends in serial amniocenteses in normal pregnancy, a graph was made depicting serial amniocenteses where four or more were done in the same patient and the pregnancy fell in the “normal” group (Fig. 3). These curves show the same trend as the “normal” mean values confirming that there is a progressive upward trend in amniotic fluid creatinine in the individual patient during pregnancy. To further study the relationship between amniotic fluid creatinine and weight and maturity of the fetus, 47 amniotic fluid creatinine values measured on samples taken by amniocentesis within one week of delivery (excluding stillbirths) were plotted against
maturity and against birth weight (Figs. 4 and 5). Coefficients of correlation were calculated and found to be fairly good. Coefficient of correlation between weeks gestation and amniotic fluid creatinine was 0.67, and between birth weight and amniotic fluid creatinine 0.66. Uric acid. Aminotic fluid uric acid was determined in 253 samples of amniotic fluid (Table I). When plotted against maturity, amniotic fluid uric acid showed a wide scattering of values as opposed to the narrower range found for creatinine. There was an upward trend in amniotic fluid uric acid with increasing gestational age as confirmed in the table of means. Electrolytes. Three hundred and thirtytwo samples of amniotic fluid were analyzed for sodium, chloride, and potassium (Table I). Electrolyte values, although more widely scattered than creatinine showed more of a trend than uric acid values. Although mean values of sodium tended to stay in the range for normal serum throughout pregnancy there was a slight progressive fall toward term. Amniotic fluid chloride showed a similar progressive fall toward term but at slightly higher levels than normal serum. Potassium values tended to remain in the range of normal serum throughout preg-
Volume Number
106 3
Contents
of
amniotic
fluid
32Y
t 0.5
t,
I
21
23
I
1
I
I
I
I
,
25
27
29
31
33
35
37
WEEKS
Fig. 3. Serial amniocenteses compared to “normal” nancy with a slight rise to term. sodium, chloride, and potassium not seem to show any definite severity of the hemolytic disease in
Uric acid, values did trend with utero.
OF GESTATION
mean values.
Table II. Amniotic
Of the biochemical changes studied, the most useful seemed to be that of amniotic fluid creatinine. The over-all results showed a progressive rise in amniotic fluid creatinine toward term, the slope increasing after 34 weeks’ gestation. There was a surprisingly small difference between the “normal” and “abnormal” mean values, the difference increasing toward term. Our results agree fairly closely with those of Pitkin and Zwirek.ll Our “normal” mean for amniotic fluid creatinine 36 weeks to term was 1.9 mg. per 100 ml. and theirs was 2.0 mg. per 100 ml. A comparison of mean values is shown in Table II. ‘Pitkin and Zwirek’sll results suggest a continued increase in amniotic fluid creatinine from 40 to 42 weeks. We were unabIe to verify this as our group did not contain any postterm pregnancies. In our “normal”
creatinine
T.G.H.
Gestation (weeks)
Comment
fluid
mean values
20-23 24-27 28-3 1 32-35 36-40 40 +
“normals” No. 9 8 30 48 31 -
Pitkin
1 Mean
No.
) Mean
0.80 0.95 1.16 1.54 1.90 -
3 ;
0.87 0.96 1.18 1.47 2.03 2.80
9 9 4
group a creatinine of 1.6 mg. per 100 ml. or greater indicated a maturity of 37 weeks or more in 90 per cent of cases. This observation could be of value to the practising obstetrician considering an indicated induction. The significance of the trend of amniotic fluid creatinine with gestation is of interest. The over-all trend of values and of serial values in individual patients presumably reflects both increasing maturity and weight of the fetus. Similarly amniotic fluid creatinine Ievels taken within one week of delivery correlated well with both weight and matur-
330
Doran,
Bjerre,
and
Porter Amer.
ity of the fetus. Studies of intrauterine growth retardation might provide further information regarding this relationship. The lower amniotic fluid creatinine values in stillbirths with decline in serial values could reflect a failure of growth. Similarly, Cherryl*
-
2 2.5z c z 2.1 -
-
6'0 I
’
32
L
I
I
I
WEEKS
I
1
44
40
36
OF GESTATION
Fig. 4. Amniotic fluid creatinine versus maturity when sample taken within one week of delivery.
x
3.3-
2.9
-
11
2.0
2.4
a
2.8
‘1
11
”
1
3.2
3.6
4.0
4..4
WEIGHT
Fig. 5. Amniotic pf delivery.
fluid creatinine
1, 1970 Gym.
found a low amniotic fluid serum creatinine ratio in association with fetal morbidity and mortality. Previous investigators have demonstrated increasing concentrations of creatinine, uric acid, and urea in amniotic fluid with gestationlsT I3 and have demonstrated fetal micturition in utero as a probable source for changes in these substances. 2o Undoubtedly, fetal urinary function, decreasing amniotic volume near term, and diffusion gradients of creatinine across amniotic membranes”l play a role in influencing amniotic fluid creatinine levels. The exact interrelationship of these factors will only be elucidated by sophisticated balance studies. Changes in amniotic fluid uric acid and electrolytes levels during pregnancy, although interesting, are probably not clearly enough defined to be of value as tests for fetal maturity. The minimal downward trend of amniotic fluid sodium and chloride toward term has been previously reported,2”’ s but the slight upward trend of amniotic fluid potassium within the normal range for serum has not, to our knowledge, been reported. The significance of these changes is not apparent.
3.32.9
February J. Obstet.
versus newborn
weight
‘I
4.8
kg
when sample taken within
one week
Volume 106 Number 3
It
is
Contents
our
creatinine
conclusion
tion
to
fetal
maturity.
We
in
amniotic
changes
the
normal” it
increasing
can
be
utiIized
index
of
fluid
amniotic
addi-
show
number need
of
to know
fluid
pregnancies
as an
amniotic
is a valuable
that
determination
creatinine
before in
all
maturity.
indices more in
suggesting obstetric
Other
of
about
tests
ple
of tests
diction
that
results logic
on
(bilirubin
promise.
of
“ab-
situations new
fluid
We
amniotic
of data
sessment
and
suggest fluid
be done may
of amniotic
will of fetal
tests
fat
that
with
provide
the
a battery of
Correlation a more
also a sam-
accuracy
clinical
331
cells)
when
is obtained,
so that
be enhanced.
these
fluid
of and
accurate
prethe
radioas-
maturity.
REFERENCES
6. 7.
8. 9. 10. 11. 12. 13.
Bevis, D. C. A.: Lancet 2: 443, 1950. Liley, A. W.: AMER. J. OBSTET. GYNEC. 83: 1359, 1961. Freda, V. J.: AMER. J. OBSTET. GYNEC. 92: 341, 1965. Bowman, I. M., and Pollock, R. T.: Pediatrics 35: 815,‘i965.. Jeffcoate, T. N. A., Fliegner, J. R. H., Russell, S. H., Davis, J. C., and Wade, A. P.: Lancet’2: 553; 1965.. ’ Nadler, H. L.: J. Pediat. 74: 132, 1969. Be&her, N. A., Brown, J. B., and Townsend, L.: AMER. J. OBSTET. GYNEC. 103: 496, 1969. Mandelbaum, B., LaCroix, G. C., and Robinson, A. R.: Obstet. Gynec. 29: 471, 1967. Brosens, H., and Gordon, H.: Obstet. Gynec. 30: 652, 1967. Bishop, E. H., and Carson, S.: ADIER. J. OBSTET. GYNEC. 102: 654, 1968. Pitkin, R. N., and Zwirek, S. J.: AMER. J. OBSTET. GYNEC. 98: 1135, 1967. Cherry, S. H.: Bull. Sloane Hosp. 13: 81, 1967. Bjerre, S., Gold, C. C., Wilson, R., and Discussion DR.
GEORGE
B. MAUGHAN,
Montreal,
Quebec.
Dr. Doran must be congratulated for a very extensive and precise testing of the various parameters outlined in the title. The results conform very well with the scant literature on the subject. By serial determinations in many instances he has gone a step further than any reported work. In interpreting the levels in amniotic fluid of the components analyzed, we must look on the amniotic fluid as one of three fluid compartments in the pregnant woman which are kept by transudation, filtration, secretion and excretion more or less in balance. The maternal serum and interstitial fluid is one component, the fetus the second component, and the amniotic fluid itself the third component. All of these by the abovenoted processes contribute to, and subtract from, the contents of the amniotic fluid, keeping it more or less in balance.
14. 15. 16. 17. 18.
19. 20.
21.
22.
23.
Doran, T. A.: AMER. J. OBSTET. GYNEC. 102: 275, 1968. Bjerre, s.: Clin. Chem. 12: 551, 1966. Technicon Comoration. Ardslev. New York, Method 11B for AutoAnalyze;,. 1965. Brown, R. A., and Freier, E.: Clin. Biochem. 1: 154, 1967. Technicon Corporation, Ardsley, New York, Method N-21A-for AutoAnalyzk;, 1965. Makeueace. A. W.. Fremont-Smith. F.. Dailey, M. E’., ancl Carroll, M. P.: Sdrg.’ Gynec: Obstet. 53: 635, 1931. Serr, D. M., Czaczkes, J. W., and Zuckerman, H.: Obstet. Gynec. 21: 551, 1963. Chez, R. A., Smith, F. G., and Hutahinson, D. L.: AMER. J. OBSTET. GYNEC. 90: 128, 1964. McGaughey, H. S., Jr., Corey, E. L., Scoggin, W. A., FickIen, C. H., and Thornton, W. N., Jr.: AMER. J. OBSTET. GYNEC. 80: 108, 1960. Battaglia, F., Prystowsky, H., Smisson, C., Hellegers, A., and Bruns, P. D.: Surg. Gynec. Obstei. 169: 509, 1969. Bonsnes. R. W.: Clin. Obstet. Gvnec. 9: 440. 1966. ’
I was struck by the higher potassium levels in amniotic fluid in the severely affected cases and cases resulting in stillbirth. I hope Dr. Doran can speculate as to whether these higher potassium levels represent terminal metabolic acidosis in the fetus in question. Dr. Doran points out, as did Pitkin in 1967, that only the creatinine levels beyond 34 weeks’ gestation are different from maternal serum or interstitial fluid levels. During intrauterine development of the fetus, the nephrogenic zone in the kidney is gradually disappearing until at 36 weeks’ gestation it has completely disappeared and the fetal kidney at this time, at least histologically, is the same as the adult organ. While normal decrease in amniotic fluid volume, with resultant concentration, may serve as an explanation of the higher amniotic creatinine levels, as may the increased muscle mass of the fetus, I would like Dr. Doran to express his opinion as to whether these levels
332
Doran,
Bjerre,
and
Porter
merely represent increased urinary excretion of creatinine by the fetus. Dr. Low’s paper to follow may well give us the answer by demonstrating that the maternal kidney, on more or less constant daily excretion of creatinine, cannot cope with the creatinine excretion of the fetus as well. The increased amniotic fluid creatinine level may well be an index of fetal kidney function and if so, of the fairly constant disappearance of the nephrogenic zone at 36 weeks. Desquamated fetal skin cells and now creatinine levels in amniotic fluid, may both be used as indices of fetal maturity, but, of course, their estimation still requires amniocentesis. In spite of our modern free-wheeling entry into the amniotic sac during pregnancy, there are some dangers to both fetus and mother associated with this procedure. We have the other commonly used clinical milestones which require relatively simple arithmetic as indices and we have radiologic evidence of ossification centers (useful in
Amer.
February J. Obstet.
1, 1970 Gynec.
all but fetal growth retardation problems) as laboratory evidence of maturity. Modern radiologic techniques should not be associated with infant or childhood leukemias and I would expect that only in the event of failure of these techniques to give a definitive answer would amniocentesis be resorted to for positive evidence. Under the circumstances in which Dr. Doran has used creatinine levels in amniotic fluid as an index of fetal maturity, where amniocentesis must be done for other reasons, the assay of creatinine levels is excellent supportive evidence of fetal maturity in assessment of the best time for induction of labor. Under circumstances in which amniocentesis would be used simply as an index of maturity alone, I would deplore its use as an unnecessary hazard. May I congratulate Dr. Doran on a painstaking and precise addition to our knowledge of the environment to which we are all subjected during our first 9 months of life.
106 number 3 I, 1970
February
hetican
Journal
of Obstetrics and Gynecology Transactions Annual
of
Meeting
Obstetricians
the
Twenty-fifth
of the
Society
and
of
Gynaecologists
of Canada
Creatinine, uric acid, and electrolytes
in amniotic
fluid T.
A.
S.
BJERRE,
DORAN,
C.
J.
PORTER,
Toronto,
Ontario
M.D. M.Sc. PH.D.
Four hundred samples of amniotic fluid obtained by amniocentesis, mostly from Rh-sensitized patients, were analyzed for creatinine, uric acid, sodium, potassium, and chloride. Amniotic fluid creatinine values were below 1 mg. per 100 ml. before 28 weeks and about 2 mg. per 100 ml. close to term. Eighty-six per cent of all creatinine values at 37 weeks’ gestation or more were at or aboue 1.6 mg. per 100 ml. Serial creatinine values in stillbirths were generally low and showed a decline. There was good correlation between creatinine values and both birth weight and maturity of infants born within one week of amniocentesis. Amniotic fluid uric acid increased with gestational age with a fairly wide scatter. Values for sodium and chloride stayed approximately in the range of those for normal serum with a slight progressive fall to term. Potassium values stayed within normal serum values but showed a slight rise to term. Amniotic fluid creatinine showed the most definite trend with gestational age and thus is a useful test for fetal maturity.
S I N c E Bevisl in 1950 described the use of amniocentesis to study bile pigments in amniotic fluid, it has become an increasingly useful technique in the assessment of the
Rh-isoimmunized patient.2p 3l 4 More recently, other substances in amniotic fluid have been studied61 6* T and there has been an interest in the use of amniocentesis in the assessment of fetal maturity. Amniotic fluid has been examined for maturity both cytologically and biochemically. Mandelbaum* demonstrated a progressive fall in amniotic fluid bilirubin in normal pregnancy where no Rh sensitization occurred. He has suggested that the absence of the 450 p peak is
From the Departments of Obstetrics and Gynaecology and Biochemistry, Toronto General Hospital. Presented at the Twenty-fifth Annual Meeting of the Society of Obstetricians and Gynecologists of Canada, Toronto, Ontario, ]une 13-15, 1969.
325
326
Doran,
Bjerre,
and
Porter
indicative of fetal maturity greater than 36 weeks. Brosens and Gordon9 and Bishop and CorsonlO have demonstrated an increasing percentage of fat cells of fetal sebaceous origin in the amniotic fluid with maturity and suggest that this is a good test for fetal maturity. Pitkin and Zwirekll studied amniotic fluid creatinine obtained by amniocentesis in 120 patients. Forty-seven of these patients had medical comphcations and 73 had uncomplicated pregnancies. They found that the level of amniotic fluid creatinine remained constant or increased very little to 34 weeks, when an abrupt rise took place so that after 37 weeks the level was 2 mg. per 100 ml. or higher in 94 per cent of patients. They felt that this assay could be a useful test of fetal maturity. CherryI” measured amniotic fluid creatinine to maternal serum creatinine ratio in 60 patients, 22 of whom were diabetic. He found an increasing content of creatinine in amniotic fluid with gestational age and a decreased ratio of amniotic fluid creatinine to maternal serum creatinine in diabetes. Over the past 4 years we have utilized amniocentesis in our hospital on almost all Rh-sensitized patients and in addition, have provided a spectrophotometric analysis service on amniotic fluid samples sent in from four other hospitals in our area. A small number of control samples of amniotic fluids from therapeutic abortion specimens were collected. In addition to measuring amniotic fluid bilirubin on these samples,13 we have measured creatinine, uric acid, and electrolytes as well as some enzymes not covered in this paper. I* Our purpose here is to report on our findings with particular emphasis on the measurement of amniotic fluid creatinine and its relationship to maturity. Unquestionably, situations arise in obstetrics where intervention is contemplated and where a reliable test for fetal maturity would be invaluable. Materials
and
methods
Four hundred and twenty-six amniotic fluids by amniocentesis were studied. For technical reasons it was not possible to do multiple biochemical determinations on all
Amer.
February J. Obstet.
1, 1970 Gynec.
the amniotic fluids obtained. There were 119 single amniocenteses and 307, serial ranging from 2 to 6 amniocenteses in the same patient. Three hundred and sixty-nine amniotic fluid samples were measured for creatinine. These samples were grouped as follows : Controls 8 Unaffected 57 Mildly affected 66 Moderately affected 133 Severely affected 49 Stillbirths 56 Controls, unaffected and mildly affected were grouped as “normal” and moderately affected, severely affected, and stillbirths as “abnormal.” The fluid was centrifuged, filtered and creatinine content was measured by a modification of the Jaf?‘C picric acid method.15 -4mniotic fluid uric acid was measured in 253 samples by the method of Browne and Freier.16 Sodium, potassium, and chloride were measured simultaneously in 333 samples by the AutoAnalyzer method.17 Results
Creatinine. Fig. 1 summarizes results obtained for creatinine levels in all amniotic fluid samples. Although there was a smaller number of samples up to 24 weeks’ gestation, levels seemed to remain constant during this period. There was a gradual increase from 24 to 34 weeks’ gestation, then a more abrupt increase from 34 weeks to term. Creatinine values were generally below 1 mg. per 100 ml. at less than 28 weeks and were at about 2 mg. per 100 ml. near term. Eighty-six per cent of all creatinine values at 37 weeks’ gestation or more were at or above 1.6 mg. per 100 ml. at 37 weeks’ gestation or more were at or above 1.6 mg. per 100 ml. In an effort to reduce the effect of Rh sensitization, mean values for the “normal” and “abnormal” groups were calculated and plotted at two weekly intervals (Fig. 2). The stippled area represents two standard deviations from the normal mean values. The mean values for the “abnormal” group were slightly lower than the “normal” group throughout
Volume Number
Contents
106 3
4.0
F
3.2
0
SlILlBIRTHS
.
SEVERELY AFFECTLO
I
MOD, UNAFFECTED AND CONTROtS
of
amniotic
fluid
327
WEEKS OF GESTATION Fig.
1. Amniotic
2.8
fluid
creatinine
levels-all
samples.
•“N~RMAL”MEAN
VALUES
b”ABNORMAL”MEAN
2.4
-
2.0
-
1.6
-
1.2
-
.a
-
VALUES
5 8 7 : ii i F z 25
.4
x
t t
12
I
i
16
I
20
I
I
24 WEEKS Of
‘Fig. 2. “Normal” and represents two standard
“abnormal” deviations
amniotic fluid from the “normal”
I
1
I
28
1
1
1
32
36
40
QESTATION creatinine mean mean values.
values.
The
stippled
area
328
Doran,
Bjerre,
and
Porter Amer.
Table
I. Mean
values for amniotic 13-29% No.
fluid
creatinine,
uric 30-34%
weeks Mean
No.
February J. Obstet.
1, 1970 Gynec.
acid, electrolytes weeks
Above
Mean
No.
35 1
weeks Mean
31
0.97
53
1.40
47
1.88
76
0.87
104
1.24
58
1.65
Normal Uric Acid Abnormal
22
5.09
33
6.05
26
6.42
57
4.92
73
5.81
37
6.74
Normal Sodium Abnormal
27
136.74
45
134.58
39
132.89
70
140.18
95
136.55
51
132.80
Normal Chloride Abnormal
27
112.70
45
111.62
39
111.05
70
115.06
96
112.66
51
110.59
27
4.01
45
4.30
39
4.54
69
4.10
96
4.24
51
4.57
Normal
Creatinine Abnormal
Normal Potassium Abnormal
pregnancy, the difference increasing after 32 weeks’ gestation. The “normal” mean value for creatinine from 36 weeks to term was 1.9 mg. per 100 ml. and the “abnormal” mean in the same gestational period was 1.8 mg. per 100 ml. Amniotic fluid creatinine values for stillbirths were generally low and serial values tended to show a decline (Fig. 1) . Mean values for three gestational periods for “normals” and “abnormals” are shown in Table I. As illustrated in Fig. 2 there was a small progressive difference between “normal” and “abnormal” mean creatinine levels in each gestational age bracket. To illustrate creatinine trends in serial amniocenteses in normal pregnancy, a graph was made depicting serial amniocenteses where four or more were done in the same patient and the pregnancy fell in the “normal” group (Fig. 3). These curves show the same trend as the “normal” mean values confirming that there is a progressive upward trend in amniotic fluid creatinine in the individual patient during pregnancy. To further study the relationship between amniotic fluid creatinine and weight and maturity of the fetus, 47 amniotic fluid creatinine values measured on samples taken by amniocentesis within one week of delivery (excluding stillbirths) were plotted against
maturity and against birth weight (Figs. 4 and 5). Coefficients of correlation were calculated and found to be fairly good. Coefficient of correlation between weeks gestation and amniotic fluid creatinine was 0.67, and between birth weight and amniotic fluid creatinine 0.66. Uric acid. Aminotic fluid uric acid was determined in 253 samples of amniotic fluid (Table I). When plotted against maturity, amniotic fluid uric acid showed a wide scattering of values as opposed to the narrower range found for creatinine. There was an upward trend in amniotic fluid uric acid with increasing gestational age as confirmed in the table of means. Electrolytes. Three hundred and thirtytwo samples of amniotic fluid were analyzed for sodium, chloride, and potassium (Table I). Electrolyte values, although more widely scattered than creatinine showed more of a trend than uric acid values. Although mean values of sodium tended to stay in the range for normal serum throughout pregnancy there was a slight progressive fall toward term. Amniotic fluid chloride showed a similar progressive fall toward term but at slightly higher levels than normal serum. Potassium values tended to remain in the range of normal serum throughout preg-
Volume Number
106 3
Contents
of
amniotic
fluid
32Y
t 0.5
t,
I
21
23
I
1
I
I
I
I
,
25
27
29
31
33
35
37
WEEKS
Fig. 3. Serial amniocenteses compared to “normal” nancy with a slight rise to term. sodium, chloride, and potassium not seem to show any definite severity of the hemolytic disease in
Uric acid, values did trend with utero.
OF GESTATION
mean values.
Table II. Amniotic
Of the biochemical changes studied, the most useful seemed to be that of amniotic fluid creatinine. The over-all results showed a progressive rise in amniotic fluid creatinine toward term, the slope increasing after 34 weeks’ gestation. There was a surprisingly small difference between the “normal” and “abnormal” mean values, the difference increasing toward term. Our results agree fairly closely with those of Pitkin and Zwirek.ll Our “normal” mean for amniotic fluid creatinine 36 weeks to term was 1.9 mg. per 100 ml. and theirs was 2.0 mg. per 100 ml. A comparison of mean values is shown in Table II. ‘Pitkin and Zwirek’sll results suggest a continued increase in amniotic fluid creatinine from 40 to 42 weeks. We were unabIe to verify this as our group did not contain any postterm pregnancies. In our “normal”
creatinine
T.G.H.
Gestation (weeks)
Comment
fluid
mean values
20-23 24-27 28-3 1 32-35 36-40 40 +
“normals” No. 9 8 30 48 31 -
Pitkin
1 Mean
No.
) Mean
0.80 0.95 1.16 1.54 1.90 -
3 ;
0.87 0.96 1.18 1.47 2.03 2.80
9 9 4
group a creatinine of 1.6 mg. per 100 ml. or greater indicated a maturity of 37 weeks or more in 90 per cent of cases. This observation could be of value to the practising obstetrician considering an indicated induction. The significance of the trend of amniotic fluid creatinine with gestation is of interest. The over-all trend of values and of serial values in individual patients presumably reflects both increasing maturity and weight of the fetus. Similarly amniotic fluid creatinine Ievels taken within one week of delivery correlated well with both weight and matur-
330
Doran,
Bjerre,
and
Porter Amer.
ity of the fetus. Studies of intrauterine growth retardation might provide further information regarding this relationship. The lower amniotic fluid creatinine values in stillbirths with decline in serial values could reflect a failure of growth. Similarly, Cherryl*
-
2 2.5z c z 2.1 -
-
6'0 I
’
32
L
I
I
I
WEEKS
I
1
44
40
36
OF GESTATION
Fig. 4. Amniotic fluid creatinine versus maturity when sample taken within one week of delivery.
x
3.3-
2.9
-
11
2.0
2.4
a
2.8
‘1
11
”
1
3.2
3.6
4.0
4..4
WEIGHT
Fig. 5. Amniotic pf delivery.
fluid creatinine
1, 1970 Gym.
found a low amniotic fluid serum creatinine ratio in association with fetal morbidity and mortality. Previous investigators have demonstrated increasing concentrations of creatinine, uric acid, and urea in amniotic fluid with gestationlsT I3 and have demonstrated fetal micturition in utero as a probable source for changes in these substances. 2o Undoubtedly, fetal urinary function, decreasing amniotic volume near term, and diffusion gradients of creatinine across amniotic membranes”l play a role in influencing amniotic fluid creatinine levels. The exact interrelationship of these factors will only be elucidated by sophisticated balance studies. Changes in amniotic fluid uric acid and electrolytes levels during pregnancy, although interesting, are probably not clearly enough defined to be of value as tests for fetal maturity. The minimal downward trend of amniotic fluid sodium and chloride toward term has been previously reported,2”’ s but the slight upward trend of amniotic fluid potassium within the normal range for serum has not, to our knowledge, been reported. The significance of these changes is not apparent.
3.32.9
February J. Obstet.
versus newborn
weight
‘I
4.8
kg
when sample taken within
one week
Volume 106 Number 3
It
is
Contents
our
creatinine
conclusion
tion
to
fetal
maturity.
We
in
amniotic
changes
the
normal” it
increasing
can
be
utiIized
index
of
fluid
amniotic
addi-
show
number need
of
to know
fluid
pregnancies
as an
amniotic
is a valuable
that
determination
creatinine
before in
all
maturity.
indices more in
suggesting obstetric
Other
of
about
tests
ple
of tests
diction
that
results logic
on
(bilirubin
promise.
of
“ab-
situations new
fluid
We
amniotic
of data
sessment
and
suggest fluid
be done may
of amniotic
will of fetal
tests
fat
that
with
provide
the
a battery of
Correlation a more
also a sam-
accuracy
clinical
331
cells)
when
is obtained,
so that
be enhanced.
these
fluid
of and
accurate
prethe
radioas-
maturity.
REFERENCES
6. 7.
8. 9. 10. 11. 12. 13.
Bevis, D. C. A.: Lancet 2: 443, 1950. Liley, A. W.: AMER. J. OBSTET. GYNEC. 83: 1359, 1961. Freda, V. J.: AMER. J. OBSTET. GYNEC. 92: 341, 1965. Bowman, I. M., and Pollock, R. T.: Pediatrics 35: 815,‘i965.. Jeffcoate, T. N. A., Fliegner, J. R. H., Russell, S. H., Davis, J. C., and Wade, A. P.: Lancet’2: 553; 1965.. ’ Nadler, H. L.: J. Pediat. 74: 132, 1969. Be&her, N. A., Brown, J. B., and Townsend, L.: AMER. J. OBSTET. GYNEC. 103: 496, 1969. Mandelbaum, B., LaCroix, G. C., and Robinson, A. R.: Obstet. Gynec. 29: 471, 1967. Brosens, H., and Gordon, H.: Obstet. Gynec. 30: 652, 1967. Bishop, E. H., and Carson, S.: ADIER. J. OBSTET. GYNEC. 102: 654, 1968. Pitkin, R. N., and Zwirek, S. J.: AMER. J. OBSTET. GYNEC. 98: 1135, 1967. Cherry, S. H.: Bull. Sloane Hosp. 13: 81, 1967. Bjerre, S., Gold, C. C., Wilson, R., and Discussion DR.
GEORGE
B. MAUGHAN,
Montreal,
Quebec.
Dr. Doran must be congratulated for a very extensive and precise testing of the various parameters outlined in the title. The results conform very well with the scant literature on the subject. By serial determinations in many instances he has gone a step further than any reported work. In interpreting the levels in amniotic fluid of the components analyzed, we must look on the amniotic fluid as one of three fluid compartments in the pregnant woman which are kept by transudation, filtration, secretion and excretion more or less in balance. The maternal serum and interstitial fluid is one component, the fetus the second component, and the amniotic fluid itself the third component. All of these by the abovenoted processes contribute to, and subtract from, the contents of the amniotic fluid, keeping it more or less in balance.
14. 15. 16. 17. 18.
19. 20.
21.
22.
23.
Doran, T. A.: AMER. J. OBSTET. GYNEC. 102: 275, 1968. Bjerre, s.: Clin. Chem. 12: 551, 1966. Technicon Comoration. Ardslev. New York, Method 11B for AutoAnalyze;,. 1965. Brown, R. A., and Freier, E.: Clin. Biochem. 1: 154, 1967. Technicon Corporation, Ardsley, New York, Method N-21A-for AutoAnalyzk;, 1965. Makeueace. A. W.. Fremont-Smith. F.. Dailey, M. E’., ancl Carroll, M. P.: Sdrg.’ Gynec: Obstet. 53: 635, 1931. Serr, D. M., Czaczkes, J. W., and Zuckerman, H.: Obstet. Gynec. 21: 551, 1963. Chez, R. A., Smith, F. G., and Hutahinson, D. L.: AMER. J. OBSTET. GYNEC. 90: 128, 1964. McGaughey, H. S., Jr., Corey, E. L., Scoggin, W. A., FickIen, C. H., and Thornton, W. N., Jr.: AMER. J. OBSTET. GYNEC. 80: 108, 1960. Battaglia, F., Prystowsky, H., Smisson, C., Hellegers, A., and Bruns, P. D.: Surg. Gynec. Obstei. 169: 509, 1969. Bonsnes. R. W.: Clin. Obstet. Gvnec. 9: 440. 1966. ’
I was struck by the higher potassium levels in amniotic fluid in the severely affected cases and cases resulting in stillbirth. I hope Dr. Doran can speculate as to whether these higher potassium levels represent terminal metabolic acidosis in the fetus in question. Dr. Doran points out, as did Pitkin in 1967, that only the creatinine levels beyond 34 weeks’ gestation are different from maternal serum or interstitial fluid levels. During intrauterine development of the fetus, the nephrogenic zone in the kidney is gradually disappearing until at 36 weeks’ gestation it has completely disappeared and the fetal kidney at this time, at least histologically, is the same as the adult organ. While normal decrease in amniotic fluid volume, with resultant concentration, may serve as an explanation of the higher amniotic creatinine levels, as may the increased muscle mass of the fetus, I would like Dr. Doran to express his opinion as to whether these levels
332
Doran,
Bjerre,
and
Porter
merely represent increased urinary excretion of creatinine by the fetus. Dr. Low’s paper to follow may well give us the answer by demonstrating that the maternal kidney, on more or less constant daily excretion of creatinine, cannot cope with the creatinine excretion of the fetus as well. The increased amniotic fluid creatinine level may well be an index of fetal kidney function and if so, of the fairly constant disappearance of the nephrogenic zone at 36 weeks. Desquamated fetal skin cells and now creatinine levels in amniotic fluid, may both be used as indices of fetal maturity, but, of course, their estimation still requires amniocentesis. In spite of our modern free-wheeling entry into the amniotic sac during pregnancy, there are some dangers to both fetus and mother associated with this procedure. We have the other commonly used clinical milestones which require relatively simple arithmetic as indices and we have radiologic evidence of ossification centers (useful in
Amer.
February J. Obstet.
1, 1970 Gynec.
all but fetal growth retardation problems) as laboratory evidence of maturity. Modern radiologic techniques should not be associated with infant or childhood leukemias and I would expect that only in the event of failure of these techniques to give a definitive answer would amniocentesis be resorted to for positive evidence. Under the circumstances in which Dr. Doran has used creatinine levels in amniotic fluid as an index of fetal maturity, where amniocentesis must be done for other reasons, the assay of creatinine levels is excellent supportive evidence of fetal maturity in assessment of the best time for induction of labor. Under circumstances in which amniocentesis would be used simply as an index of maturity alone, I would deplore its use as an unnecessary hazard. May I congratulate Dr. Doran on a painstaking and precise addition to our knowledge of the environment to which we are all subjected during our first 9 months of life.