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The effect of gestational age on amniotic fluid glucose in pregnancy complicated by diabetes mellitus
The effect of gestational age on amniotic fluid glucose in pregnancy complicated by diabetes mellitus SHARON
L.
NC)!-D
DOOLEY,
E. MET%GER,
RlCHARD
DEPP.
M.D. M.D.
M.D.
SORKERI‘
1;REISKE:L.
M.D.
RICHARD
I..
M.D.
(.YII~(I~~.
I’HELPS,
Illihc
Amniotic fluid glucose was measured in 189 amniotic fluid samples from 117 well-controlbd Class A to F diabetic pregnant women from 32 to 40 weeks’ gestation. A simultaneous maternal plasma glucose level was determined at each amniocentesis. Samples were obtained with the mother in the fasting or nonfasting (3.8 hours after breavast) state. Amniotic fluid glucose correlated significantly with simultaneous maternal glucose (r = 0.562; p = 0.001). A sigM~%M dwvnward linear trend of mean amniotic fluid glucose with advancing gestatkmai age was &mor@~m (p < 0.01). No Wend of mean simultaneous maternal glucose with gestational age was seen. These feet& were not affected by maternal prandial status at the time of amniocentesis. It is conoluded that amniotic fluid glucose decreases with advancing gestational age in well-controlled di&etii pregnant women Independent of maternal glycemic levels. Studies of amniotic fluid glucose and/or its relationship to other metabolic hormones must take this into account. (AM. J. OBSTET. GYNECOL. 142:492, 1982.)
If .4s Kb:EN co~~siderable interest in determining if’ amniotic fluid glucose (,\FG) Iweis reflect llie metabolic milieu of’ the fttus. In spite of’ this interest. neither the source, turnover rate, nor fate of’ glucose in amniotic ftuid has been determined. In normal pregnay, ;\FG levels correlate with simultaneous maternal glucose concentrations ’ ’ and rise acutelv in response to 2 marernal glucose load.“. ” Aclctitionall~-, lhe co~lcentration of’ AFG diminishes with advancing gestational age. ‘. ’ akhough the ph) siologic basis for this obser\ ccl phenomenon is not clear. ‘1.14 t.RE:
492
Studies of .4FG in preqx~ncies c-omplicated h!- diabetes mellitus have demonstrated levels higher than those observed in normal pregnancy.“- ‘. ‘-!I There is general agreement that AFG correlates with maternal glycemia at the time of’ amniocentesis as in nondiabetic gestation.“. ‘I’ However, there are confiicting reports as to whether or not the AFG concentration f’alls with advancing gestational age.“. ‘. I’. ‘I Contiol for the timing of’amniocentesis in relatioil to mau3~nal prxidial status \vas considered in only one 01’ thehe rraports.’ IlIvestigators to (Iilk lxtvr not ass wed maternal glucose levels at the time of amniocentc is to demonstrate the presence or absence of a gestatic *ial age ef’fkct independent of’ the potential influencr I f changing matei-nal diabetic control. The potential conf’ounding eftect ot :esrational age must be delineated if’ amniotic gtucc~e , to be evatuatecl as a metabolic indicator of’ feeal sta 11s in pregnancy complicated by cliabetes mellitus. This is relevant whether ,4FG is studied atone or concurre.iTIs with metabolic hormones, e.g., inwlin, C-peptidr, glwa~ot~. and/or growth hormone. The present report examkes the inHuence of advancing gesrational age on AFG concentration in pregnant w&en with welt-controlled di0002-9378/X2/050492+05$~.50/0
0
1982 I‘hc c: Y. MOSb\ co.
Effect of gestafional age on amniotic fluid glucose 493
Table I. Distribution prandial status
of amniocenteses by maternal
32-33 wk
34-35 wk
36-37 wk
238 wk
Total
17
46
38 33
23 17
124 65 189
F NF
15
F = Fasting; iXF = nonfasting (see text for definition) Table II. Correlation of AFG with plasma SMG by prandial status and gestational age r
N
P
0.590
124
O..i26
65
0.001 0.001
All we&:
F NF F + NF: 32-33 wk
:34-35 wk 36-37 wk ~38 wk
0.655
17
0.004
0.616
61
0.001
0.527
71 40
0.001 0.001
0.490
F = Fasting: NF = nonfasting. ahetes, with attention to both timing of amniocentesis in relation to maternal prandial status and concurrent maternal glycemic control. Material and methods A total of’ 189 transabdominal amniocenteses were performed on I 17 patients from 32 to 40 weeks’ gestation. All women were consenting participants in the Sorthwestern L.niversity Diabetes in Pregnancy Center. The subjects were grouped by classes according to the criteria ot \2’hite,lzJ as I modified by Phelps and associates” f’or qestational diabetes. Insulin-dependent diabetic \vomen rver-e hospitalized for variable periods prior to deli\,ery depending upon their classification and the presence or absence of pregnancy complications. Diabetic control was achieved by multiple-dose insulin administration; regular insulin was given before major meals and intermediate-acting insulin was given once or tlvice daily. In-hospital glycemic control was monitored tvith daily f’asting and premeal plasma glucose deter-minations and intermittent Z-hour postprandial and 3:OO A M determinations. (;estational age eras determined by reliable menstrtlal tlates lvhen confirmed by ultrasound age determined b\ fetal biparietal diameter. When there was a large discrepant!- bcttveen sonographic and menstrual according to the age, gestational aqe was assiqned ‘ method of Depp.‘” Dubowitz examination of the neonate demonstrated excellent agreement with obstetric age.
Fig. 1. AFG and plasma SMG (mean t SEW versus gestational age in all study patients. N = Number of paired maternal and amniotic Huid samples at each gestational age interval. * = Significant linear rrend at the p < 0.01 level.
Amniocenteses were performed for assessment of fetal pulmonary maturity. The first amniocentesis was performed at approximately 34 weeks’ gestation, with repeal assessment at P-week inter\rals whenever feasible. When the placenta was anterior by ultrasonographic localization, the first amniocentesis was deferred until 36 weeks unless specificall)- indicated b) fetal risk. All amniocenteses at ~34 weeks were performed with the patient in the fasting state (overnight fast). Amniocenteses after 34 weeks were randomly carried out in the fasting or nonfasting maternal state. If a patient underwent any subsequent amniocentesis, it was performed in the prandial state opposite to the previous one. Nonfasting amniocenteses were performed an average of 3.8 hours after breakfast, when maternal glucose concentration was expected to have returned to premeal levels. Breakfjst consisted of two se\Tenths of the daily dietar), intake of 38 kcalikg of’ ideal body weight and contained 45% carbohydrate. At the time of amniocentesis, an aliquot of’ amniotic Huid was obtained in a sterile container for glucose analysis. Immediately prior to amniocentesis, a 3 to 5 ml maternal peripheral venous blood sample was obtained in a heparinized tllbe for glucose analysis. Both amniotic fluid and maternal samples were transported promptly to the laboratory and centrifuged; supernate
494
Dooley et al.
Table III. Correlation of AFG with maternal glucose in hospitalized patients
.4F(; versus SM<; AF(; versus MM(;
plasma
r
N
P
0.633 0.634
83 x3
0.001 0.00 1
See text f’or definition of AF<;. SM<;. and MM(;. Table IV. AFG and SMG (mean 2 SEM) by gestational age and maternal prandial status
All patient,\: AFG (mgidl) F”
32-33 wk 34-35 urk 36-37 wk
~38 ulk
38 t 3 (46) .4i + 6 (15)
28 ‘- 2 (38) 34 5 2 (33)
26 + 2 (23) 33 k 5 (li)
100 k 5 102 ” 7 (17) (46) 101 t 9 (15)
86 2 5 (38) 86 -c 6 (33)
88 + 6 (23) 107 t 14 (17)
27 2 3 (22) 36 i 3
2.5 It 4 (N 35 ? 7 (12)
42 2 ?I
(17:) SM(; (mgidl) F NF Cla.~se.c B to F:
AFC; (mgidi) F* NFP SMG (mg/dl) F NF
47 + 6 (12) -
40 2 4 (33) .il 2 7 (9)
cm
105 r 7 113 ? 8 92 k 7 (33) (12) (22) 93 2 11 96 -c Y (20) (9)
100 * I3 (8) 122 -c 18
(12)
F = Fasting; NF = nonfasting. *Significant linear trend at p < 0.01 level. tNumber of observations. $Significant linear trend at p < 0.05 level. FtBorderline significant linear trend (0.10 > p > 0.05). or plasma was frozen at - 20” C for subsequent analysis. Glucose determinations were made in duplicate with glucose osidase on a Beckman Glucose Analyzer. Therefore. each amniocentesis yielded paired AFG and simultaneous maternal plasma glucose (SMG) samples. For some of the analyses, maternal glycemic control was assessed for the clay prior to amniocentesis. A mean maternal glucose (MMG) was calculated as the mean of fasting and premeal glucoses during the 24 hours prior to amniocentesis up to and including the SMG. The following statistical methods were used: unpaired Student’s t test, linear correlation, and one-wa) analysis of variance (ANOVA) with tests for (1) overall difference between time periods and (2) linear temporal trends with advancing gestational age.
Results
I-he 1 Ii study patients were distributed according IO White’s classes as ti~llows: Class A, 50; Class B. Z’,H;C:kss C, 16; Class I>, 10; Class F, Z3.Sixty-three patients underwent a single amniocentesis, and 5-t patients had two or more determinations. All amniotic Rrritl \pecimens were tiec of 0, erT meconium or blood. No Iilltowarcl effects of atnniorentcsis wel-c i~o,c(l. For the purpose of’ analysis, result4 were grouped into P-week gestational age inter\ als. .I’he distribution of amniocenteses according to prandial status of. the mother and gestational age interval is shown in Table I. One patient had two amniocenteses performed within one gestation;il age interval. ‘l‘\\.o patients underwent an amniocentesis at 40 weeks; these 1vt.t.e includecl in the ~38 week categort Relationship of AFG to maternal glycemia. A significant linear correlation between amniotic Huid glucose and simultaneous maternal glucose was demonstrated for the 189 paired samples in the total group (r = 0.562: p = 0.001). Results of analyses subdivided by maternal prandial status are shown in Table Il. .4 significant linear correlation between AFG and SMG was seen in the fasting samples. when the metabolic condition would be expected to be most stable. ‘This significant relationship was maintained in separate analysis of the nonfasting samples in spite of. the tnetabolic perturbation of a recent meal. Accordingl) , fasting and nonfasting values were pooled to examine the relationship between AFG and SMG within the various gestational age intervals (Table 11). A significant linear correlation was maintained at all gestational ages. The I-elationship between ;\I:(; and SMG was examined in greater detail on a subgroup of’ XX amniocenteses performed on 54 hospitalized patients, all having Class B to F diabetes. The correlation between XE‘(; and SMG in this group (l’able III) was similat- to that observed when all of the values were atlalyzed together (see above and Table 1 I). Additionally, nlaternal glycemic control was assessed for the ‘L&hour period prior to amniotic fluid sampling in this subgroup 1,~ calculation of’ MMG for each amniocentesis. A bighI!significant correlation was found between AH; and MMG (Table III). Relationship of AFG and maternal glycemia to advancing gestational age. Values for mean (*SEM) AFG and SMG according to gestationat age intervals for all 189 paired samples are depicted in Fig. 1. Analysis h! one-way ANOVA demonstrated a significant difference between time periods for mean AFG (p < O.Ol), and linear regression analysis showed a significant downward trend with advancing gestationat age
Effect of gestational age on amniotic fluid glucose 495
(p < 0.01). There were no significant differences between time periods and no significant temporal trend for mean SMG which could account for the observed changes in AFG. The significant temporal trend for AFG was maintained when the data were analyzed separately by fasting and nonfasting prandial status at the time of amniocentesis (Table IV). Again, no temporal trends were found f’or the corresponding fasting and nonfasting mean SMG values, and there were no significant differences between time intervals. As seen in Table IV, AFG tended to be slightly higher in nonfasting groups than in fasting groups. However the difference was significant only in the Class B to F determinations in the 36- to 37-week interval, where the fasting and nonfasting values were 27 and 36 mgidl, respectively (unpaired t, p < 0.05). Analysis of trends of AFG and SMG was perf’ormed separately in women with Class B to F diabetes who were intensely treated with multiple-dose insulin. Thus, the gfycemic control of’ these predominantly hospitalized patients was quite stable over the time period of amniotic fluid sampling, allowing a more critical interpretation of’changes in AFG. The results are shown in the lower portion of Tahle I\‘. It is seen that the same progressive decline in AFG occurs with advancing gestational age, although this showed only borderline significancein the smaller subgroupofnonfastingsamples. Ko corresponding decline in simultaneous maternal glucose could be demonstrated, and, as predicted, these values remained quite stable with advancing gestational age.
Comment Little is known about the source and fate of AFG. The mother, f’etopfacental unit, and amniotic fluid are a complex and intimately related three-compartment system wflich renders such investigation difficult. The confirmation in this study of a correlation between maternal and amniotic fluid glucose levels does not preclude a fetal contribution of‘ glucose to amniotic fluid. The rapid transpfacentaf transfer of glucose to the fetus b) f’acifitated dif’fusion maintains the fetal plasma concentrations profmrtionate to maternal levels. Whether ot‘maternal or fetal source, AFG may fluctuate acuteI> in response to changing concentrations in the maternaf-fetal compartments. Greco and associates” observed a peak AFG concentration 30 minutes f’oflowing an intravenous glucose load in normal pregnant women, with return to near baseline levels by 90 minutes. Our results in diabetic pregnancy are consistent with their findings. We observed minimal difference between fasting and nonfasting AFG levels when the latter determinations
were made an average of 3.8 hours postprandially. Our demonstration of a significant correlation of AFG with MMG levels for 24 hours prior to amniocentesis does not address this issue ofsourceof AFG but is in keeping with the concept of an intimately related three-compartment system. The physiologic mechanism(s) responsible for diminishing AFG with advancing gestational age remains uncertain. Fetal urine is likely to be a significant source of‘ AFG. It could be postulated that maturation of fetal renal tubular function results in increased reabsorption of’ filtered glucose, thus decreasing this contribution with advancing gestationat age. Additionally, maturation of fetal gastrointestinal function may increase the clearance of’ AFG by means of fetal swallowing and gut ahsorption. Glucose ma) also transfer directly into amniotic fluid across the amnion. The amnion is known to metabofize glucose actively”’ and to be fess permeable to glucose with advancing gestationat age.” A potential influence of the maturing placenta on glucose homeostasis in the conceptus might also be implicated because of’ the high rate of gtycolysis in this organ.“, ” Any or all of’these factors may be involved in the gestational age ef’fect on AFG. In the fIresent studies we have observed diminishing AFG levels with advancing gestation in diabetic pregnant women that cannot be attributed to changes in mateI-nat gtycemic control. Our demonstration of this phenomenon in the maternal postprandial state as weft as the fasting state may have been possible because of excellent control in a large series of diabetic patients. Previously reported concentrations of AFG in late gestation in diabetic pregnant women range from 21 to >200 mg/dl,“+“, +I1 with most in the range of 60 to 70 mgidf. Our mean levels were considerably lower than these. It is also possible that the maturational events leading to diminishing AFG may themselves be inHuellced by maternal metabolic control and thus be more easily demonstrable in a well-controlled diabetic population. Regardless of the factors involved, our results indicate that studies of AFG and/or of its refationship to other metabolic factors or hormones must take into account a decrease in AFG with advancing gestation in the diabetic state as in the normal state. We acknowledge the help of’the research nurses of the Diabetes in Pregnancy Center and the staf’f of the Clinical Research Center for their participation in the care of’ flatients and the securing of samples. We are particularly indebted to Naomi Vaisrub, Ph.D., for her assistance in statistical analysis, and to Barbara Jones and the staff of’the biometry unit for their aid in data handling.
496
Dooley et al.
REFERENCES
1~ Kim. 1’. J., and Felig, P.: Maternal and amniotic fluid stthstrate levels during caloric deprivation in human pregnancy, Metabolism 21:507, 1972. 2. Wood, C.. Acharya, P. T’., Cornwell, E., and Pinkerton, ,J, H. M.: The significance of glucose and lactic acid concentration in the amniotic fluid, J. Obstet. Gynaecol. Br. Commons. 70~274, 1963. 3. Archimaur. G., Belizan, J. M., Ross, pi. A., and Althabe, 0.: Glucose concentration in amniotic Huid: Its possible signiticance in diabetic pregnancy, AM. J. OBSTET. GYNECOL. 119:596, 1974. 4. Spellacy. N’. N., Buhi, W. C., Bradley, B., and Holsinger, li. K.: Maternal, fetal and amniotic Huid levels of glucose, insulin and growth hormone, Obstet. Gynecol. 41:323. 19iY. j, Peclersen, J,: Glucose content of the amniotic Huid in diahetic prenancies: Correlations with the maternal blood sugar, Acta Endocrinol. 15:342, 1954. 6. Grew. A. V., Rebuzzi, A. G., Bellati, CT., Serri, F., Altomonte, L., Manna, R., and Ghirlanda, G.: Fetal origin of amniotic Huid insulin in the human mother, Clin. Endocrinol. 12:6i, 1980. 7. DraLancic, A., and Kuvacic, I.: Amniotic fluid glucose concentration, AM. J. OBSTET. GYNECOL. 120~40, 1974. X. Vewman, R. L., and Tutera, G.: The glucose-insulin ratio in amniotic fluid, Obstet. Gvnecol. 47:599, 1976. 9. l‘chobroutsky, G., Heard, I., Tchobroutsky, C., and Eschwege, E.: Amniotic Huid C-peptide in normal and insulin-dependent diabetic pregnancies, Diabetologia 18: 289, 1980. IO. Seed. X. El.. Leung, L. S., Tabor, >I, W., and Russell, P. ‘I-.: Changes in amniotic Huid glucose, /3- hydroxy-buryrate, glycerol, and lactate concentration in diabetic pregnancy, AM. J, OBSTET. GYNECOL. 135:887, 1979.
Il. 12. 13. 14.
15.
16.
17. 18.
19.
Cassady, G., Blake, M., Bailey, P., Younger, B., and Sunners, ,J.: Amniotic Huid glucose in pregnancies complicated by diabetes, AM. J. OBSTET. GYNLCOL. 127:21. 1977. Wood, G. P., and Sherline, D. M.: Amniotic fluid glucow: A maternal, fetal. and neonatal correlation. .-\M. 1, OBSTET.GYNECOL. 112:151,1975. Nelson, H. El., Gillespie, L.. and \Vhitc, I’.: Pregnant\ complicated hv diabetes mellitus. Obstet. Gvnewl. 1:219. 1953. Phelps, R. L., Metrgrr, B. E., and t;wirtkrl, S.: Iledlc;tI management of diabetes in pregnancy, ire Sciarra. J. ,J.. editor, and Depp, R.. associate editor: <;ynecolog) and Obstetrics, Hagerstown, Maryland, 1979, vol. 3. Harpcl& Row, Publisher, Inc., chap. 13. Depp, R.: Dynamics of fetal growth, rrr Sabbagha, K. E.. editor: Diagnostic C‘ltrasound Applied to Obstetric+ and Gynecolog,y, Hagerstown, Maryland. 1980, Harper & Roiv, Pubhshers, Inc.. chap. 1 I, p. 1 II. SchbvartL. A. L., Forster, (1. S., Smith, 1’. \.. and L.&gin\. G. (:.: Human amnion metabolism. ;\M. .I. ~hWI’E:l GYNECOI.. 127:470, 1977. Marin, R. D.. and Hood, W.: Signil~cance ot ammo& f-luid glucose in late pregnant), Aust. N. %. J. Obstet. Gynaecol. 19:91, 1979. Freinkel, N.: Effects of the conceptus on maternal metabolism during pregnant?, in Leihel B. S., and Wrenshall (;. A., editors: On the Nature and Treatment of Diabetcc. hmsterdam, 1965, Excerpta Medica Foundation. pp. 679-691. Burd, I.. I.. Jones. M. D., Jr., Simmon.\. .lf. A., Makrwski. F.. I... Meschia, G.. and Battaglia. F. (Z.: Placental production and foetdl utilisation of lactate ancl p\‘ruvate, Naturr 254:710. 1975.
L.
NC)!-D
DOOLEY,
E. MET%GER,
RlCHARD
DEPP.
M.D. M.D.
M.D.
SORKERI‘
1;REISKE:L.
M.D.
RICHARD
I..
M.D.
(.YII~(I~~.
I’HELPS,
Illihc
Amniotic fluid glucose was measured in 189 amniotic fluid samples from 117 well-controlbd Class A to F diabetic pregnant women from 32 to 40 weeks’ gestation. A simultaneous maternal plasma glucose level was determined at each amniocentesis. Samples were obtained with the mother in the fasting or nonfasting (3.8 hours after breavast) state. Amniotic fluid glucose correlated significantly with simultaneous maternal glucose (r = 0.562; p = 0.001). A sigM~%M dwvnward linear trend of mean amniotic fluid glucose with advancing gestatkmai age was &mor@~m (p < 0.01). No Wend of mean simultaneous maternal glucose with gestational age was seen. These feet& were not affected by maternal prandial status at the time of amniocentesis. It is conoluded that amniotic fluid glucose decreases with advancing gestational age in well-controlled di&etii pregnant women Independent of maternal glycemic levels. Studies of amniotic fluid glucose and/or its relationship to other metabolic hormones must take this into account. (AM. J. OBSTET. GYNECOL. 142:492, 1982.)
If .4s Kb:EN co~~siderable interest in determining if’ amniotic fluid glucose (,\FG) Iweis reflect llie metabolic milieu of’ the fttus. In spite of’ this interest. neither the source, turnover rate, nor fate of’ glucose in amniotic ftuid has been determined. In normal pregnay, ;\FG levels correlate with simultaneous maternal glucose concentrations ’ ’ and rise acutelv in response to 2 marernal glucose load.“. ” Aclctitionall~-, lhe co~lcentration of’ AFG diminishes with advancing gestational age. ‘. ’ akhough the ph) siologic basis for this obser\ ccl phenomenon is not clear. ‘1.14 t.RE:
492
Studies of .4FG in preqx~ncies c-omplicated h!- diabetes mellitus have demonstrated levels higher than those observed in normal pregnancy.“- ‘. ‘-!I There is general agreement that AFG correlates with maternal glycemia at the time of’ amniocentesis as in nondiabetic gestation.“. ‘I’ However, there are confiicting reports as to whether or not the AFG concentration f’alls with advancing gestational age.“. ‘. I’. ‘I Contiol for the timing of’amniocentesis in relatioil to mau3~nal prxidial status \vas considered in only one 01’ thehe rraports.’ IlIvestigators to (Iilk lxtvr not ass wed maternal glucose levels at the time of amniocentc is to demonstrate the presence or absence of a gestatic *ial age ef’fkct independent of’ the potential influencr I f changing matei-nal diabetic control. The potential conf’ounding eftect ot :esrational age must be delineated if’ amniotic gtucc~e , to be evatuatecl as a metabolic indicator of’ feeal sta 11s in pregnancy complicated by cliabetes mellitus. This is relevant whether ,4FG is studied atone or concurre.iTIs with metabolic hormones, e.g., inwlin, C-peptidr, glwa~ot~. and/or growth hormone. The present report examkes the inHuence of advancing gesrational age on AFG concentration in pregnant w&en with welt-controlled di0002-9378/X2/050492+05$~.50/0
0
1982 I‘hc c: Y. MOSb\ co.
Effect of gestafional age on amniotic fluid glucose 493
Table I. Distribution prandial status
of amniocenteses by maternal
32-33 wk
34-35 wk
36-37 wk
238 wk
Total
17
46
38 33
23 17
124 65 189
F NF
15
F = Fasting; iXF = nonfasting (see text for definition) Table II. Correlation of AFG with plasma SMG by prandial status and gestational age r
N
P
0.590
124
O..i26
65
0.001 0.001
All we&:
F NF F + NF: 32-33 wk
:34-35 wk 36-37 wk ~38 wk
0.655
17
0.004
0.616
61
0.001
0.527
71 40
0.001 0.001
0.490
F = Fasting: NF = nonfasting. ahetes, with attention to both timing of amniocentesis in relation to maternal prandial status and concurrent maternal glycemic control. Material and methods A total of’ 189 transabdominal amniocenteses were performed on I 17 patients from 32 to 40 weeks’ gestation. All women were consenting participants in the Sorthwestern L.niversity Diabetes in Pregnancy Center. The subjects were grouped by classes according to the criteria ot \2’hite,lzJ as I modified by Phelps and associates” f’or qestational diabetes. Insulin-dependent diabetic \vomen rver-e hospitalized for variable periods prior to deli\,ery depending upon their classification and the presence or absence of pregnancy complications. Diabetic control was achieved by multiple-dose insulin administration; regular insulin was given before major meals and intermediate-acting insulin was given once or tlvice daily. In-hospital glycemic control was monitored tvith daily f’asting and premeal plasma glucose deter-minations and intermittent Z-hour postprandial and 3:OO A M determinations. (;estational age eras determined by reliable menstrtlal tlates lvhen confirmed by ultrasound age determined b\ fetal biparietal diameter. When there was a large discrepant!- bcttveen sonographic and menstrual according to the age, gestational aqe was assiqned ‘ method of Depp.‘” Dubowitz examination of the neonate demonstrated excellent agreement with obstetric age.
Fig. 1. AFG and plasma SMG (mean t SEW versus gestational age in all study patients. N = Number of paired maternal and amniotic Huid samples at each gestational age interval. * = Significant linear rrend at the p < 0.01 level.
Amniocenteses were performed for assessment of fetal pulmonary maturity. The first amniocentesis was performed at approximately 34 weeks’ gestation, with repeal assessment at P-week inter\rals whenever feasible. When the placenta was anterior by ultrasonographic localization, the first amniocentesis was deferred until 36 weeks unless specificall)- indicated b) fetal risk. All amniocenteses at ~34 weeks were performed with the patient in the fasting state (overnight fast). Amniocenteses after 34 weeks were randomly carried out in the fasting or nonfasting maternal state. If a patient underwent any subsequent amniocentesis, it was performed in the prandial state opposite to the previous one. Nonfasting amniocenteses were performed an average of 3.8 hours after breakfast, when maternal glucose concentration was expected to have returned to premeal levels. Breakfjst consisted of two se\Tenths of the daily dietar), intake of 38 kcalikg of’ ideal body weight and contained 45% carbohydrate. At the time of amniocentesis, an aliquot of’ amniotic Huid was obtained in a sterile container for glucose analysis. Immediately prior to amniocentesis, a 3 to 5 ml maternal peripheral venous blood sample was obtained in a heparinized tllbe for glucose analysis. Both amniotic fluid and maternal samples were transported promptly to the laboratory and centrifuged; supernate
494
Dooley et al.
Table III. Correlation of AFG with maternal glucose in hospitalized patients
.4F(; versus SM<; AF(; versus MM(;
plasma
r
N
P
0.633 0.634
83 x3
0.001 0.00 1
See text f’or definition of AF<;. SM<;. and MM(;. Table IV. AFG and SMG (mean 2 SEM) by gestational age and maternal prandial status
All patient,\: AFG (mgidl) F”
32-33 wk 34-35 urk 36-37 wk
~38 ulk
38 t 3 (46) .4i + 6 (15)
28 ‘- 2 (38) 34 5 2 (33)
26 + 2 (23) 33 k 5 (li)
100 k 5 102 ” 7 (17) (46) 101 t 9 (15)
86 2 5 (38) 86 -c 6 (33)
88 + 6 (23) 107 t 14 (17)
27 2 3 (22) 36 i 3
2.5 It 4 (N 35 ? 7 (12)
42 2 ?I
(17:) SM(; (mgidl) F NF Cla.~se.c B to F:
AFC; (mgidi) F* NFP SMG (mg/dl) F NF
47 + 6 (12) -
40 2 4 (33) .il 2 7 (9)
cm
105 r 7 113 ? 8 92 k 7 (33) (12) (22) 93 2 11 96 -c Y (20) (9)
100 * I3 (8) 122 -c 18
(12)
F = Fasting; NF = nonfasting. *Significant linear trend at p < 0.01 level. tNumber of observations. $Significant linear trend at p < 0.05 level. FtBorderline significant linear trend (0.10 > p > 0.05). or plasma was frozen at - 20” C for subsequent analysis. Glucose determinations were made in duplicate with glucose osidase on a Beckman Glucose Analyzer. Therefore. each amniocentesis yielded paired AFG and simultaneous maternal plasma glucose (SMG) samples. For some of the analyses, maternal glycemic control was assessed for the clay prior to amniocentesis. A mean maternal glucose (MMG) was calculated as the mean of fasting and premeal glucoses during the 24 hours prior to amniocentesis up to and including the SMG. The following statistical methods were used: unpaired Student’s t test, linear correlation, and one-wa) analysis of variance (ANOVA) with tests for (1) overall difference between time periods and (2) linear temporal trends with advancing gestational age.
Results
I-he 1 Ii study patients were distributed according IO White’s classes as ti~llows: Class A, 50; Class B. Z’,H;C:kss C, 16; Class I>, 10; Class F, Z3.Sixty-three patients underwent a single amniocentesis, and 5-t patients had two or more determinations. All amniotic Rrritl \pecimens were tiec of 0, erT meconium or blood. No Iilltowarcl effects of atnniorentcsis wel-c i~o,c(l. For the purpose of’ analysis, result4 were grouped into P-week gestational age inter\ als. .I’he distribution of amniocenteses according to prandial status of. the mother and gestational age interval is shown in Table I. One patient had two amniocenteses performed within one gestation;il age interval. ‘l‘\\.o patients underwent an amniocentesis at 40 weeks; these 1vt.t.e includecl in the ~38 week categort Relationship of AFG to maternal glycemia. A significant linear correlation between amniotic Huid glucose and simultaneous maternal glucose was demonstrated for the 189 paired samples in the total group (r = 0.562: p = 0.001). Results of analyses subdivided by maternal prandial status are shown in Table Il. .4 significant linear correlation between AFG and SMG was seen in the fasting samples. when the metabolic condition would be expected to be most stable. ‘This significant relationship was maintained in separate analysis of the nonfasting samples in spite of. the tnetabolic perturbation of a recent meal. Accordingl) , fasting and nonfasting values were pooled to examine the relationship between AFG and SMG within the various gestational age intervals (Table 11). A significant linear correlation was maintained at all gestational ages. The I-elationship between ;\I:(; and SMG was examined in greater detail on a subgroup of’ XX amniocenteses performed on 54 hospitalized patients, all having Class B to F diabetes. The correlation between XE‘(; and SMG in this group (l’able III) was similat- to that observed when all of the values were atlalyzed together (see above and Table 1 I). Additionally, nlaternal glycemic control was assessed for the ‘L&hour period prior to amniotic fluid sampling in this subgroup 1,~ calculation of’ MMG for each amniocentesis. A bighI!significant correlation was found between AH; and MMG (Table III). Relationship of AFG and maternal glycemia to advancing gestational age. Values for mean (*SEM) AFG and SMG according to gestationat age intervals for all 189 paired samples are depicted in Fig. 1. Analysis h! one-way ANOVA demonstrated a significant difference between time periods for mean AFG (p < O.Ol), and linear regression analysis showed a significant downward trend with advancing gestationat age
Effect of gestational age on amniotic fluid glucose 495
(p < 0.01). There were no significant differences between time periods and no significant temporal trend for mean SMG which could account for the observed changes in AFG. The significant temporal trend for AFG was maintained when the data were analyzed separately by fasting and nonfasting prandial status at the time of amniocentesis (Table IV). Again, no temporal trends were found f’or the corresponding fasting and nonfasting mean SMG values, and there were no significant differences between time intervals. As seen in Table IV, AFG tended to be slightly higher in nonfasting groups than in fasting groups. However the difference was significant only in the Class B to F determinations in the 36- to 37-week interval, where the fasting and nonfasting values were 27 and 36 mgidl, respectively (unpaired t, p < 0.05). Analysis of trends of AFG and SMG was perf’ormed separately in women with Class B to F diabetes who were intensely treated with multiple-dose insulin. Thus, the gfycemic control of’ these predominantly hospitalized patients was quite stable over the time period of amniotic fluid sampling, allowing a more critical interpretation of’changes in AFG. The results are shown in the lower portion of Tahle I\‘. It is seen that the same progressive decline in AFG occurs with advancing gestational age, although this showed only borderline significancein the smaller subgroupofnonfastingsamples. Ko corresponding decline in simultaneous maternal glucose could be demonstrated, and, as predicted, these values remained quite stable with advancing gestational age.
Comment Little is known about the source and fate of AFG. The mother, f’etopfacental unit, and amniotic fluid are a complex and intimately related three-compartment system wflich renders such investigation difficult. The confirmation in this study of a correlation between maternal and amniotic fluid glucose levels does not preclude a fetal contribution of‘ glucose to amniotic fluid. The rapid transpfacentaf transfer of glucose to the fetus b) f’acifitated dif’fusion maintains the fetal plasma concentrations profmrtionate to maternal levels. Whether ot‘maternal or fetal source, AFG may fluctuate acuteI> in response to changing concentrations in the maternaf-fetal compartments. Greco and associates” observed a peak AFG concentration 30 minutes f’oflowing an intravenous glucose load in normal pregnant women, with return to near baseline levels by 90 minutes. Our results in diabetic pregnancy are consistent with their findings. We observed minimal difference between fasting and nonfasting AFG levels when the latter determinations
were made an average of 3.8 hours postprandially. Our demonstration of a significant correlation of AFG with MMG levels for 24 hours prior to amniocentesis does not address this issue ofsourceof AFG but is in keeping with the concept of an intimately related three-compartment system. The physiologic mechanism(s) responsible for diminishing AFG with advancing gestational age remains uncertain. Fetal urine is likely to be a significant source of‘ AFG. It could be postulated that maturation of fetal renal tubular function results in increased reabsorption of’ filtered glucose, thus decreasing this contribution with advancing gestationat age. Additionally, maturation of fetal gastrointestinal function may increase the clearance of’ AFG by means of fetal swallowing and gut ahsorption. Glucose ma) also transfer directly into amniotic fluid across the amnion. The amnion is known to metabofize glucose actively”’ and to be fess permeable to glucose with advancing gestationat age.” A potential influence of the maturing placenta on glucose homeostasis in the conceptus might also be implicated because of’ the high rate of gtycolysis in this organ.“, ” Any or all of’these factors may be involved in the gestational age ef’fect on AFG. In the fIresent studies we have observed diminishing AFG levels with advancing gestation in diabetic pregnant women that cannot be attributed to changes in mateI-nat gtycemic control. Our demonstration of this phenomenon in the maternal postprandial state as weft as the fasting state may have been possible because of excellent control in a large series of diabetic patients. Previously reported concentrations of AFG in late gestation in diabetic pregnant women range from 21 to >200 mg/dl,“+“, +I1 with most in the range of 60 to 70 mgidf. Our mean levels were considerably lower than these. It is also possible that the maturational events leading to diminishing AFG may themselves be inHuellced by maternal metabolic control and thus be more easily demonstrable in a well-controlled diabetic population. Regardless of the factors involved, our results indicate that studies of AFG and/or of its refationship to other metabolic factors or hormones must take into account a decrease in AFG with advancing gestation in the diabetic state as in the normal state. We acknowledge the help of’the research nurses of the Diabetes in Pregnancy Center and the staf’f of the Clinical Research Center for their participation in the care of’ flatients and the securing of samples. We are particularly indebted to Naomi Vaisrub, Ph.D., for her assistance in statistical analysis, and to Barbara Jones and the staff of’the biometry unit for their aid in data handling.
496
Dooley et al.
REFERENCES
1~ Kim. 1’. J., and Felig, P.: Maternal and amniotic fluid stthstrate levels during caloric deprivation in human pregnancy, Metabolism 21:507, 1972. 2. Wood, C.. Acharya, P. T’., Cornwell, E., and Pinkerton, ,J, H. M.: The significance of glucose and lactic acid concentration in the amniotic fluid, J. Obstet. Gynaecol. Br. Commons. 70~274, 1963. 3. Archimaur. G., Belizan, J. M., Ross, pi. A., and Althabe, 0.: Glucose concentration in amniotic Huid: Its possible signiticance in diabetic pregnancy, AM. J. OBSTET. GYNECOL. 119:596, 1974. 4. Spellacy. N’. N., Buhi, W. C., Bradley, B., and Holsinger, li. K.: Maternal, fetal and amniotic Huid levels of glucose, insulin and growth hormone, Obstet. Gynecol. 41:323. 19iY. j, Peclersen, J,: Glucose content of the amniotic Huid in diahetic prenancies: Correlations with the maternal blood sugar, Acta Endocrinol. 15:342, 1954. 6. Grew. A. V., Rebuzzi, A. G., Bellati, CT., Serri, F., Altomonte, L., Manna, R., and Ghirlanda, G.: Fetal origin of amniotic Huid insulin in the human mother, Clin. Endocrinol. 12:6i, 1980. 7. DraLancic, A., and Kuvacic, I.: Amniotic fluid glucose concentration, AM. J. OBSTET. GYNECOL. 120~40, 1974. X. Vewman, R. L., and Tutera, G.: The glucose-insulin ratio in amniotic fluid, Obstet. Gvnecol. 47:599, 1976. 9. l‘chobroutsky, G., Heard, I., Tchobroutsky, C., and Eschwege, E.: Amniotic Huid C-peptide in normal and insulin-dependent diabetic pregnancies, Diabetologia 18: 289, 1980. IO. Seed. X. El.. Leung, L. S., Tabor, >I, W., and Russell, P. ‘I-.: Changes in amniotic Huid glucose, /3- hydroxy-buryrate, glycerol, and lactate concentration in diabetic pregnancy, AM. J, OBSTET. GYNECOL. 135:887, 1979.
Il. 12. 13. 14.
15.
16.
17. 18.
19.
Cassady, G., Blake, M., Bailey, P., Younger, B., and Sunners, ,J.: Amniotic Huid glucose in pregnancies complicated by diabetes, AM. J. OBSTET. GYNLCOL. 127:21. 1977. Wood, G. P., and Sherline, D. M.: Amniotic fluid glucow: A maternal, fetal. and neonatal correlation. .-\M. 1, OBSTET.GYNECOL. 112:151,1975. Nelson, H. El., Gillespie, L.. and \Vhitc, I’.: Pregnant\ complicated hv diabetes mellitus. Obstet. Gvnewl. 1:219. 1953. Phelps, R. L., Metrgrr, B. E., and t;wirtkrl, S.: Iledlc;tI management of diabetes in pregnancy, ire Sciarra. J. ,J.. editor, and Depp, R.. associate editor: <;ynecolog) and Obstetrics, Hagerstown, Maryland, 1979, vol. 3. Harpcl& Row, Publisher, Inc., chap. 13. Depp, R.: Dynamics of fetal growth, rrr Sabbagha, K. E.. editor: Diagnostic C‘ltrasound Applied to Obstetric+ and Gynecolog,y, Hagerstown, Maryland. 1980, Harper & Roiv, Pubhshers, Inc.. chap. 1 I, p. 1 II. SchbvartL. A. L., Forster, (1. S., Smith, 1’. \.. and L.&gin\. G. (:.: Human amnion metabolism. ;\M. .I. ~hWI’E:l GYNECOI.. 127:470, 1977. Marin, R. D.. and Hood, W.: Signil~cance ot ammo& f-luid glucose in late pregnant), Aust. N. %. J. Obstet. Gynaecol. 19:91, 1979. Freinkel, N.: Effects of the conceptus on maternal metabolism during pregnant?, in Leihel B. S., and Wrenshall (;. A., editors: On the Nature and Treatment of Diabetcc. hmsterdam, 1965, Excerpta Medica Foundation. pp. 679-691. Burd, I.. I.. Jones. M. D., Jr., Simmon.\. .lf. A., Makrwski. F.. I... Meschia, G.. and Battaglia. F. (Z.: Placental production and foetdl utilisation of lactate ancl p\‘ruvate, Naturr 254:710. 1975.