Brrtish Journal of Obstetrics and Gynaecology February 1977. Vol84. pp 98-107
A CRITICAL EVALUATION OF TESTS USED TO ASSESS GESTATIONAL AGE BY
R. F. HARRISON, Senior Registrar and Lecturer * A. P. ROBERTS, Lecturer AND
S. CAMPBELL, Professor of Clinical Obstetrics and Gynaecology Institute of Obstetrics and Gynaecology, Queen Charlotte’s Hospital, London Summary The reliability of eight methods for estimating gestational age in the third trimester of pregnancy has been assessed in patients with fetuses of known maturity. Late ultrasound cephalometry, amniotic fluid creatinine estimations and lecithin/ sphingomyelin ratio were found t o be significantly more reliable than the other five methods. The mean of estimated gestational ages provided by the three techniques used in combination gave a significantly more accurate prediction of fetal age than any single test and allowed formation of a ‘maturity profile’. and five biochemical tests have been assessed to determine if any test, or combination of tests, could give a ‘maturity profile’ which was of optimal clinical value.
AN accurate assessment of fetal maturity is necessary in order to undertake safely many of the prophylactic procedures which have been introduced into current obstetric practice. A previous study at Queen Charlotte’s Maternity Hospital (Dewhurst et al, 1972) has shown an increase in perinatal mortality from 14 t o 61 per 1000 when gestational age was unknown. While impeccable menstrual data (Lind, 1970) or early ultrasound fetal measurements (Campbell, 1969; Robinson, 1974) give the best indications of fetal age, there are many occasions when such data are not available. Previous work (Underhill et al, 1971) has shown that late ultrasound cephalometry is of more predictive value than radiology or amniotic fluid cytology. A number of other tests have been reported t o be of value in the determination of gestational age in the third trimester of pregnancy. In the present report, amniotic fluid cytology, late ultrasound cephalometry
PATIENTS AND METHODS Patients All patients were attending the antenatal clinic at Queen Charlotte’s Maternity Hospital, London. The gestational age of each patient was reliable, having been calculated either from impeccable menstrual data, using Naegele’s calculation, and confirmed by estimation of uterine size at first visit, or from early (before 20 weeks) ultrasound biparietal diameter measurements (Campbell, 1969). This is subsequently referred to as the actual gestational age. A total of 91 patients had amniocentesis performed for various reasons in the third trimester of pregnancy. Methodology and the minimal complications arising have been reported more fully elsewhere (Harrison et al,
* Present
Address: Consultant and Senior Lecturer, TCD Unit at the Rotunda Hospital, Dublin, Ireland 98
ASSESSMENT OF GESTATIONAL AGE
1975). Two patients required more than one tap and two went spontaneously into labour within 24 hours of the amniocentesis.
Amniotic fluid cytology Nile blue sulphate test (Brosens and Gordon, 1966). The maturity criteria modifications suggested by Sharma and Trussell (1970) were used to group the gestational age assessment as less than 34 weeks, 34 to 38 weeks, or more than 38 weeks. The results were compared with the actual gestational age and recorded as correct or incorrect. Haematoxylin and eosin stain (Lind et al, 1971). The results were scored as up to 32 weeks, 33 to 36 weeks, and 37 weeks or over. Results were then compared with the actual gestational age and recorded as correct or incorrect. The Lind scoring system (Lind, 1973) which utilizes cytology, creatinine and amniotic/serum urea difference was also employed, as it is suggested that this improves cytological prediction value. Biochemical tests Urea. Amniotic fluid urea levels were measured by the method described by Gillibrand (1969). Using the mean data provided, a line was fitted to the graph of Lind et a1 (1971) and used to estimate gestational age. Later graphs (Lind, 1973) may, however, have improved upon this, although they are constructed from urea for given gestation and it is possible that a different line would be produced for gestation for given urea. Urea diference. The maternal serum urea was measured by the method described by Gillibrand (1969) and the values obtained were subtracted from the relevant amniotic fluid urea value. The difference obtained was used to calculate the estimated gestational age from the graphs provided by Lind and Billewicz (1971). Uric acid. Amniotic fluid uric acid levels were measured by the method of Brown (1945) and the estimated gestational age was obtained from the graph of Harrison (1972). The original graph was prepared at the Rotunda Hospital, Dublin and so, in 25 samples, uric acid was measured in the laboratories of both Queen Charlotte’s Maternity Hospital and the Rotunda
99
Hospital. The mean difference in the measurements was 0.57, which was not statistically significant (t = 0.138, p>O.8). Lecithinlsphingomyelin ratio (L/S ratio). The method of Borer et a1 (1971) was used to assess the L/S ratio and the estimated gestational age was obtained from the normal values found in our own hospital (Dewhurst e f al, 1973), combined with those of Clements et a1 (1972). Creatinine. Amniotic fluid creatinine levels were measured by the Folin-Wu modification of the Jaffe reaction (Owen et al, 1954). The estimated gestational age was calculated from the graph of Harrison (1973) and, as this graph was prepared at the Rotunda Hospital, creatinine was measured in 23 samples, both in the laboratories of Queen Charlotte’s Maternity Hospital and the Rotunda. A mean difference of 0.28 was found which was not statistically significant (t = 0.271; p>O.7). Late ultrasound cephalometry. The fetal biparietal diameter was measured by the method of Campbell (1969) and the estimated gestational age obtained from the graphs of Campbell and Newman (1971).
Calculation With each of the biochemical tests and with the late cephalometry, the estimated gestational age of the fetus was given to the nearest week and recorded. The actual gestational age of the fetus was subtracted from the estimated gestational age and the difference recorded; a positive difference indicated that the test overestimated gestational age, while a negative difference indicated an underestimation. The mean difference was calculated and its significance assessed using Student’s ‘t’ test. The variance of the differences about the mean was used as a measure of the relative reliability of the tests; the variance ratio (F) test was used to assess the significance of differences in the variances. RESuLTS Amnioticfluid cytology The results of the comparison between the actual and estimated gestational ages are given in Table I. It is clear that the haematoxylin and eosin stain recommended by Lind (1970), with
100
HARRISON, ROBERTS AND CAMPBELL
combination with the haematoxylin and eosin stain gave 55 per cent correct predictions to within one week, and 82 per cent to within two weeks. The Nile blue sulphate test gave better results, correctly predicting gestational age in 73 per cent of cases, although it was disturbing to note that the actual gestational age was less than 38 weeks in 14 of 35 instances when the estimated gestational age was greater than 38 weeks. In one case the actual gestational age was only 31 weeks.
TABLE I Comparison of actual gestational age with estimated gestational age based on resulrs or cytology tests on amniotic fluid
Estimate Correct Incorrect
Test Nile blue sulphate Haematoxylin and eosin (Lind, 1970)
Total
62
23
85
31
50
81
only 38 per cent correct predictions, was not found to be sufficiently accurate to be clinically reliable. It was found difficult to differentiate between the cell types described in this method, more especially in distinguishing between fully mature anucleate cells and normally degenerating cells. Using the Lind scoring method however (Lind, 1973) creatinine and urea difference in
l6
B. Amniotic tluid urea ditference.
A. Amniotic fluid urea,
1 .
Biochemical tests on amniotic fluid and late ultrasound cephalometry The differences between the actual and estimated gestational ages from the various individual biochemical tests and by late ultrasound cephalometry are shown graphically in Figure 1, and are analyzed and compared in Table 11.
n.91
n =79
h30.132
s'. 25.352
C .Amniotic fluid uric acid.
n.92 s'=21.364
a m
z 4 -
+-
W P-
12
Q
a
U
-
6
20
6 +
4
-
O
6
&
+
10-
0
5
5
+10
THE E S T I M A T E D MINUS ACTUAL GESTATION I N WEEKS.
mg*
n
10
5
0
5+lO
E . Amniotic fluid creatinine.
-8
4
0
&
+
F. Late ccphatomelry
FIG.1 Individual tests-Comparison of differences between actual and gestational ages. The solid areas number of patients in whom the fetus in utero was thought to be small-for-dates.
(m) show
the
Late cephalometry
_-
Creatinine
85
85
85
L/S ratio
-
+1.098
92
Uric acid
-0.694
+2.165
+0.176
$0.734
79
Urea difference
+0.472
91
Urea
No. of patients
2.463 P0.4
6.667
7.163
8.028
21.364
25.352
30.430
~~
Mean difference estimated- Student’s actual ‘t’ test Variance gestation (weeks)
F ::=3.803 P
A CRITICAL EVALUATION OF TESTS USED TO ASSESS GESTATIONAL AGE BY
R. F. HARRISON, Senior Registrar and Lecturer * A. P. ROBERTS, Lecturer AND
S. CAMPBELL, Professor of Clinical Obstetrics and Gynaecology Institute of Obstetrics and Gynaecology, Queen Charlotte’s Hospital, London Summary The reliability of eight methods for estimating gestational age in the third trimester of pregnancy has been assessed in patients with fetuses of known maturity. Late ultrasound cephalometry, amniotic fluid creatinine estimations and lecithin/ sphingomyelin ratio were found t o be significantly more reliable than the other five methods. The mean of estimated gestational ages provided by the three techniques used in combination gave a significantly more accurate prediction of fetal age than any single test and allowed formation of a ‘maturity profile’. and five biochemical tests have been assessed to determine if any test, or combination of tests, could give a ‘maturity profile’ which was of optimal clinical value.
AN accurate assessment of fetal maturity is necessary in order to undertake safely many of the prophylactic procedures which have been introduced into current obstetric practice. A previous study at Queen Charlotte’s Maternity Hospital (Dewhurst et al, 1972) has shown an increase in perinatal mortality from 14 t o 61 per 1000 when gestational age was unknown. While impeccable menstrual data (Lind, 1970) or early ultrasound fetal measurements (Campbell, 1969; Robinson, 1974) give the best indications of fetal age, there are many occasions when such data are not available. Previous work (Underhill et al, 1971) has shown that late ultrasound cephalometry is of more predictive value than radiology or amniotic fluid cytology. A number of other tests have been reported t o be of value in the determination of gestational age in the third trimester of pregnancy. In the present report, amniotic fluid cytology, late ultrasound cephalometry
PATIENTS AND METHODS Patients All patients were attending the antenatal clinic at Queen Charlotte’s Maternity Hospital, London. The gestational age of each patient was reliable, having been calculated either from impeccable menstrual data, using Naegele’s calculation, and confirmed by estimation of uterine size at first visit, or from early (before 20 weeks) ultrasound biparietal diameter measurements (Campbell, 1969). This is subsequently referred to as the actual gestational age. A total of 91 patients had amniocentesis performed for various reasons in the third trimester of pregnancy. Methodology and the minimal complications arising have been reported more fully elsewhere (Harrison et al,
* Present
Address: Consultant and Senior Lecturer, TCD Unit at the Rotunda Hospital, Dublin, Ireland 98
ASSESSMENT OF GESTATIONAL AGE
1975). Two patients required more than one tap and two went spontaneously into labour within 24 hours of the amniocentesis.
Amniotic fluid cytology Nile blue sulphate test (Brosens and Gordon, 1966). The maturity criteria modifications suggested by Sharma and Trussell (1970) were used to group the gestational age assessment as less than 34 weeks, 34 to 38 weeks, or more than 38 weeks. The results were compared with the actual gestational age and recorded as correct or incorrect. Haematoxylin and eosin stain (Lind et al, 1971). The results were scored as up to 32 weeks, 33 to 36 weeks, and 37 weeks or over. Results were then compared with the actual gestational age and recorded as correct or incorrect. The Lind scoring system (Lind, 1973) which utilizes cytology, creatinine and amniotic/serum urea difference was also employed, as it is suggested that this improves cytological prediction value. Biochemical tests Urea. Amniotic fluid urea levels were measured by the method described by Gillibrand (1969). Using the mean data provided, a line was fitted to the graph of Lind et a1 (1971) and used to estimate gestational age. Later graphs (Lind, 1973) may, however, have improved upon this, although they are constructed from urea for given gestation and it is possible that a different line would be produced for gestation for given urea. Urea diference. The maternal serum urea was measured by the method described by Gillibrand (1969) and the values obtained were subtracted from the relevant amniotic fluid urea value. The difference obtained was used to calculate the estimated gestational age from the graphs provided by Lind and Billewicz (1971). Uric acid. Amniotic fluid uric acid levels were measured by the method of Brown (1945) and the estimated gestational age was obtained from the graph of Harrison (1972). The original graph was prepared at the Rotunda Hospital, Dublin and so, in 25 samples, uric acid was measured in the laboratories of both Queen Charlotte’s Maternity Hospital and the Rotunda
99
Hospital. The mean difference in the measurements was 0.57, which was not statistically significant (t = 0.138, p>O.8). Lecithinlsphingomyelin ratio (L/S ratio). The method of Borer et a1 (1971) was used to assess the L/S ratio and the estimated gestational age was obtained from the normal values found in our own hospital (Dewhurst e f al, 1973), combined with those of Clements et a1 (1972). Creatinine. Amniotic fluid creatinine levels were measured by the Folin-Wu modification of the Jaffe reaction (Owen et al, 1954). The estimated gestational age was calculated from the graph of Harrison (1973) and, as this graph was prepared at the Rotunda Hospital, creatinine was measured in 23 samples, both in the laboratories of Queen Charlotte’s Maternity Hospital and the Rotunda. A mean difference of 0.28 was found which was not statistically significant (t = 0.271; p>O.7). Late ultrasound cephalometry. The fetal biparietal diameter was measured by the method of Campbell (1969) and the estimated gestational age obtained from the graphs of Campbell and Newman (1971).
Calculation With each of the biochemical tests and with the late cephalometry, the estimated gestational age of the fetus was given to the nearest week and recorded. The actual gestational age of the fetus was subtracted from the estimated gestational age and the difference recorded; a positive difference indicated that the test overestimated gestational age, while a negative difference indicated an underestimation. The mean difference was calculated and its significance assessed using Student’s ‘t’ test. The variance of the differences about the mean was used as a measure of the relative reliability of the tests; the variance ratio (F) test was used to assess the significance of differences in the variances. RESuLTS Amnioticfluid cytology The results of the comparison between the actual and estimated gestational ages are given in Table I. It is clear that the haematoxylin and eosin stain recommended by Lind (1970), with
100
HARRISON, ROBERTS AND CAMPBELL
combination with the haematoxylin and eosin stain gave 55 per cent correct predictions to within one week, and 82 per cent to within two weeks. The Nile blue sulphate test gave better results, correctly predicting gestational age in 73 per cent of cases, although it was disturbing to note that the actual gestational age was less than 38 weeks in 14 of 35 instances when the estimated gestational age was greater than 38 weeks. In one case the actual gestational age was only 31 weeks.
TABLE I Comparison of actual gestational age with estimated gestational age based on resulrs or cytology tests on amniotic fluid
Estimate Correct Incorrect
Test Nile blue sulphate Haematoxylin and eosin (Lind, 1970)
Total
62
23
85
31
50
81
only 38 per cent correct predictions, was not found to be sufficiently accurate to be clinically reliable. It was found difficult to differentiate between the cell types described in this method, more especially in distinguishing between fully mature anucleate cells and normally degenerating cells. Using the Lind scoring method however (Lind, 1973) creatinine and urea difference in
l6
B. Amniotic tluid urea ditference.
A. Amniotic fluid urea,
1 .
Biochemical tests on amniotic fluid and late ultrasound cephalometry The differences between the actual and estimated gestational ages from the various individual biochemical tests and by late ultrasound cephalometry are shown graphically in Figure 1, and are analyzed and compared in Table 11.
n.91
n =79
h30.132
s'. 25.352
C .Amniotic fluid uric acid.
n.92 s'=21.364
a m
z 4 -
+-
W P-
12
Q
a
U
-
6
20
6 +
4
-
O
6
&
+
10-
0
5
5
+10
THE E S T I M A T E D MINUS ACTUAL GESTATION I N WEEKS.
mg*
n
10
5
0
5+lO
E . Amniotic fluid creatinine.
-8
4
0
&
+
F. Late ccphatomelry
FIG.1 Individual tests-Comparison of differences between actual and gestational ages. The solid areas number of patients in whom the fetus in utero was thought to be small-for-dates.
(m) show
the
Late cephalometry
_-
Creatinine
85
85
85
L/S ratio
-
+1.098
92
Uric acid
-0.694
+2.165
+0.176
$0.734
79
Urea difference
+0.472
91
Urea
No. of patients
2.463 P0.4
6.667
7.163
8.028
21.364
25.352
30.430
~~
Mean difference estimated- Student’s actual ‘t’ test Variance gestation (weeks)
F ::=3.803 P
