- Email: [email protected]
Effect of maternal hydration on oligohydramnios: a comparison of three volume expansion methods
Effect of Maternal Hydration on Oligohydramnios: A Comparison of Three Volume Expansion Methods SHIGEHARU DOI, MD, HISAO OSADA, MD, KATSUYOSHI SEKI, MD, AND SOUEI SEKIYA, MD Objective: To determine the effect of maternal hydration with intravenous (IV) isotonic fluid, IV hypotonic fluid, and oral water on amniotic fluid index (AFI) in women with oligohydramnios. Methods: Patients with low AFI and gestational age over 35 weeks without maternal complications were randomized into four groups (2 L/2 h IV isotonic fluid, 2 L/2 h IV hypotonic fluid, 2 L/2 h oral water, control). Maternal plasma osmolality, AFI, hematocrit, and hemoglobin concentration were measured before and after hydration. Results: Eighty-four patients (n 5 21/group) completed the study without any maternal adverse effects. The mean increase in AFI after hydration was significantly greater in the IV hypotonic and oral water groups (2.8 6 1.9, P < .001; 3.8 6 1.9, P < .001, respectively), but not in the IV isotonic group (0.5 6 1.1), compared with the control group (0.5 6 1.1). Significant decreases in maternal hematocrit and hemoglobin concentration were found only after IV isotonic hydration (32.0 6 2.9 to 29.5 6 2.3, P < .001; 11.0 6 1.6 to 10.1 6 1.4, P < .001, respectively). Changes in maternal osmolality correlated with the changes in AFI in both the IV hypotonic group (r 5 .58, P < .001) and oral water group (r 5 .63, P < .001). Conclusion: Maternal hydration with either IV hypotonic fluid or oral water increases AFI in oligohydramnios. Maternal osmotic change rather than maternal volume expansion had a more direct impact on increasing amniotic fluid volume with short-term acute hydration.(Obstet Gynecol 1998;92:525–9. © 1998 by The American College of Obstetricians and Gynecologists.)
Oligohydramnios is a common phenomenon in postterm pregnancy and fetal growth restriction (FGR), and etiologies of reduced amniotic fluid (AF) volume may include maternal intravascular fluid depletion1 and even insensible fluid loss.2 Maternal hydration has been From the Department of Obstetrics and Gynecology, Chiba University School of Medicine, Chiba, Japan.
VOL. 92, NO. 4, PART 1, OCTOBER 1998
the focus recently of studies in women with oligohydramnios,1,3– 6 with the expectation of an increase in AF volume. The mode of administration that received the most attention in these studies was oral hydration, achieving a reduction of maternal plasma osmolality and a significant increase in amniotic fluid index (AFI).3–5 An alternative route of maternal hydration is intravenous (IV) fluid loading, which was attempted as a method of volume expansion in women who were dehydrated or hypovolemic, and this corrected oligohydramnios as well as maternal plasma volume.1,6 Importantly, AF volume has been reported to correlate with maternal plasma volume.1 Although one randomized study in women showed the benefit of IV hydration with isotonic fluid for increasing AFI,7 the effect of IV route on AF volume is still controversial. In ovine studies, isotonic maternal volume expansion through the IV route did not increase fetal urine production,8,9 which is thought to be the most important contributor to AF volume in the third trimester; however, hypotonic volume expansion increased fetal urine production.8 No reported studies in women have compared the effects of oral and IV routes of administration on AF volume. This investigation, therefore, was designed as a randomized and blinded study to compare the effects of maternal hydration with oral water, IV isotonic fluid, and IV hypotonic fluid on AF volume in women with oligohydramnios and to evaluate the processes involved in increasing AF volume.
Materials and Methods Patients with ultrasonographic diagnosis of oligohydramnios were evaluated for participation in a randomized trial after admission for induction of labor at the Division of Obstetrics and Gynecology of Chiba Uni-
0029-7844/98/$19.00 PII S0029-7844(98)00242-7
525
versity Hospital, Chiba, Japan. Oligohydramnios was diagnosed as an AFI of less than or equal to 5.0 cm of four-quadrant ultrasonographic measurement.10 This study was approved by the Chiba University Hospital Ethics Committee. The subjects met the following criteria: singleton pregnancy; well-established gestational age over 35 weeks; intact membranes; no maternal complications, such as hypertension, cardiovascular disease, hyperthyroidism, and diabetes; no evidence of preeclampsia; no fetal structural malformation; and no evidence of fetal distress on nonstress test. After obtaining written informed consent, prospective randomization was carried out by sealed-card selection into four groups as follows: 1) IV infusion of 2 L/2 h lactated Ringer’s solution as an isotonic fluid (255 mOsm/kg/H2O); 2) IV infusion of 2 L/2 h hypotonic fluid made of diluted Ringer’s solution (150 mOsm/kg/H2O); 3) oral intake of 2 L/2 h water; and 4) control group receiving a fixed slow drip for maintenance of venous route. Overhydration with acute IV infusion may elicit adverse effects such as cardiac failure and/or pulmonary edema. Therefore, we monitored serially maternal electrocardiogram (ECG), blood pressure (BP), respiratory rates, and peripheral venous pressure through an indwelling 18-gauge catheter in the antecubital vein for prevention of maternal side effects in the IV infusion groups. Changes in peripheral venous pressure have been shown to be related closely to changes in central venous pressure.11 Maternal plasma osmolality, serum sodium level, hematocrit, and hemoglobin concentration were measured before and at the end of hydration by the usual laboratory techniques. In the IV hypotonic group, we measured plasma electrolytes at least once during hydration to prevent potential hyponatremia and extensive hemolysis from occurring. All measurements of AFI and Doppler studies were performed with a 3.5-MHz transducer with pulse-wave color Doppler ultrasonography (Aloka SSD-2000, Tokyo, Japan) before hydration and at 1 hour after hydration by one ultrasonographer who was blinded to the randomization of the study groups. Measurement of AFI was performed twice on each occasion, and mean AFI was obtained by averaging the two measurements. Patients were excluded from enrollment to the study when AFI was found to be greater than 6.0 cm. The fetal renal artery was visualized as a branch from the descending aorta into the hilum of the kidney in the longitudinal view of the fetal body with color flow mapping. Velocity waveforms were recorded in the state of absent fetal breathing movements. The pulsatility index12 (PI) was calculated (PI 5 [systolic velocity -
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Table 1. Patient Characteristics
Characteristic
IV isotonic (n 5 21)
IV hypotonic (n 5 21)
Oral water (n 5 21)
Control (n 5 21)
Maternal age 28.1 (23–33) 26.3 (26 –34) 29.3 (25–35) 28.6 (22–32) (y) Parity (n) 1.3 (0 –2) 1.5 (0 –3) 1.5 (0 –2) 1.6 (0 –3) Gestational age 39.5 (35– 41) 39.7 (35– 42) 37.3 (36 – 42) 38.9 (35– 42) at study (wk) Gestational age 8 10 11 8 .41 wk (n) SGA at 4 4 6 5 delivery (n) IV 5 intravenous; SGA 5 small for gestational age.13 Data are presented as mean (range) or n.
diastolic velocity] / mean velocity), with three consecutive waveforms as renal artery resistance. The sample size was determined from our data of a preliminary study of AFI measurements in 30 cases of oligohydramnios (3.6 6 1.5 cm, mean 6 standard deviation). The initial oral hydration study by Kilpatrick et al3 demonstrated a 1.5-cm increase in AFI in women with oligohydramnios. Therefore, a power calculation indicated that approximately 20 subjects per group would be required to have 90% of power at one-sided a of .05 to detect at least a 1.5-cm increase in AFI. Eighty-four women with oligohydramnios, divided into four groups, were enrolled finally in this study. Characteristics of the patients are listed in Table 1. Maternal age, gestational age, parity, rate of FGR,13 and postterm pregnancy were similar among all groups. Data were compared by paired t test within each group. The differences of the values between prehydration and posthydration were presented as D and compared between the groups with analysis of variance followed by Fisher protected least significance difference. Linear regression analysis was performed for the correlation between D AFI and D osmolality. P , .05 was considered statistically significant.
Results There were no changes in maternal ECG, BP, and peripheral venous pressure during hydration, and no patients discontinued the study because of adverse effects. Table 2 presents the values of AFI, maternal plasma osmolality, hematocrit, and hemoglobin concentration. There were no differences in AFI, maternal osmolality, hematocrit, and hemoglobin concentration before hydration among the groups. One hour after hydration, D AFI was significantly greater in the IV
Obstetrics & Gynecology
Table 2. Changes in Amniotic Fluid Volume, Maternal Osmolality, Hematocrit, and Hemoglobin Concentration Before and After Hydration IV isotonic (n 5 21) AFI Before Change in AFI Osmolality Before Change in osmolality Hct Before After P Hb Before After P
IV hypotonic (n 5 21)
Oral water (n 5 21)
Control (n 5 21)
3.5 6 1.5 0.5 6 1.1
3.6 6 1.3 2.8 6 1.9*
3.4 6 1.5 3.8 6 1.9*
3.2 6 1.3 0.5 6 1.1
285.6 6 2.8 20.5 6 1.2
286.1 6 3.8 26.9 6 3.5*
285.1 6 3.3 28.0 6 3.8*
286.2 6 2.4 20.4 6 1.3
32.0 6 2.9 29.5 6 2.3 ,.001
31.5 6 3.2 32.2 6 3.2 NS
31.7 6 2.9 32.5 6 3.1 NS
31.0 6 3.4 31.3 6 3.1 NS
11.0 6 1.6 10.1 6 1.4 ,.001
11.2 6 1.9 11.3 6 2.0 NS
11.1 6 1.5 11.3 6 1.7 NS
10.8 6 1.3 10.9 6 1.3 NS
IV 5 intravenous; AFI 5 amniotic fluid index; Hct 5 hematocrit; P 5 significance by paired t test; NS 5 no significance; Hb 5 hemoglobin concentration. Data are presented as mean 6 standard deviation. * P , .001 includes both compared with IV isotonic group and compared with control group by analysis of variance followed by Fisher protected least significance difference.
hypotonic and oral water groups (2.8 6 1.9, P , .001; 3.8 6 1.9, P , .001, respectively) than in the control group (0.5 6 1.1), but not in the IV isotonic group (0.5 6 1.1). Similarly, D osmolality also was significantly greater in the IV hypotonic and oral water groups (2 6.9 6 3.5, P , .001; 2 8.0 6 3.8, P , .001, respectively) than in the control group (2 0.4 6 1.3), but was not higher in the IV isotonic group (2 0.5 6 1.2). On the other hand, significant decreases of maternal hematocrit and hemoglobin concentration were found only after IV isotonic hydration (32.0 6 2.9 to 29.5 6 2.3, P , .001; 11.0 6 1.6 to 10.1 6 1.4, P , .001, respectively). There was a significant correlation between D AFI and D osmolality in both IV hypotonic (r 5 .58, P , .001) and oral water groups (r 5 .63, P , .001) (Figure 1). Maternal serum sodium levels also decreased significantly after hydration in the IV hypotonic and oral water groups (138.5 6 2.0 to 130.8 6 3.8, P , .01; 139.6 6 2.4 to 130.2 6 2.5, P , .001, respectively), but not in the IV isotonic and control groups (137.2 6 1.8 to 138.4 6 3.5, not significant; 137.0 6 2.5 to 136.8 6 3.5, not significant). Table 3 demonstrates the differences between the PI values of the fetal renal artery before and after hydration in each group. No significant differences were observed among the groups.
However, with regard to oral hydration, our results showed a similar effect as in other reported studies3,4; we demonstrated that IV hydration with hypotonic fluid was equally effective for increasing the AFI. The changes in AFI correlated significantly with changes in maternal osmolality. The results suggest that maternal plasma osmotic change has a more profound impact on acute increase of AF volume when compared with maternal volume expansion through the IV route.
Discussion Our randomized study demonstrated that in women with oligohydramnios, a significant increase in the AFI was achieved by both IV hypotonic fluid loading and oral hydration, but not by IV isotonic fluid loading.
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Figure 1. Correlation between maternal osmotic change and changes in amniotic fluid index (AFI). The solid line represents the linear regression line of the oral water group (closed circles), and the dashed line represents that of the intravenous hypotonic fluid group (open circles). Osm 5 osmolality.
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Table 3. Difference in Fetal Renal Artery Pulsatility Index Before and After Hydration Renal artery
IV isotonic
IV hypotonic
Oral water
Control
Change in PI* 20.05 6 0.42 20.07 6 0.51 0.05 6 0.57 20.06 6 0.66 (n 5 16) PI 5 pulsatility index. Data are presented as mean 6 standard deviation. P values were not significant between the groups by analysis of variance followed by Fisher protected least significance difference. * Posthydration value minus prehydration value.
Goodlin et al1 showed that vigorous IV fluid loading improved the maternal “dehydrated” state, as evidenced by the decrease in both hematocrit and plasma osmolality, resulting in an increase in AF volume. In the present study, apparently “dehydrated” and “hypovolemic” women with higher plasma osmolality were not included in any of the groups. Therefore, it seems unlikely that in the IV isotonic group, maternal osmolality changes significantly in “nondehydrated” women. With respect to the physiologic principles, water transfer between mother and fetus is regulated dominantly by osmotic forces, in which electrolyte gradients determine net transplacental water exchange.14 In a recent ovine study with maternal oral water loading,15 it also was reported that a reduction of maternal fetal osmotic gradient facilitated water transfer to the fetus, leading to an increase in fetal urine production. Thus, taken together with our results, it is unlikely that acute maternal volume expansion achieves fluid shift into the fetus without maternal osmotic change. Of interest was the fact that the IV isotonic group alone showed a significant decrease in both hematocrit and hemoglobin concentration. The decrease in hemoglobin concentration may reflect the maternal plasma volume expansion in the IV isotonic group.16 It is uncertain whether plasma volume expansion failed to occur in the IV hypotonic and oral water groups. Alternatively, the lack of change in hemoglobin concentration in these groups may be explained in part by water transfer from the mother into the fetus. In contrast to our results, Chelmow et al7 found a significant increase of 5 cm in AFI in patients with premature ruptured membranes after infusion of 1L IV isotonic fluid. The reason for this conflicting finding is unclear, because the magnitudes of maternal osmotic change and plasma volume expansion were not evaluated in their study. The main source of the increase in AFI with hydration has not been identified. Flack et al4 reported that fetal urine production did not change significantly with maternal oral hydration in women with oligohydram-
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nios, as determined by ultrasonographic estimation of hourly fetal urine flow. On the other hand, recent ovine studies have demonstrated that maternal water loading with the administration of IV arginine vasopressin agonist increased fetal urine production15,17 and decreased fetal swallowing activity, resulting in a marked increase in AF volume.17 In the human fetus, Doppler velocity waveform indices of the fetal renal artery have been used to represent an indirect method for evaluation of fetal renal perfusion, and the correlations between fetal renal artery resistance and AF volume, and fetal urine production also have been investigated.18 –21 Thus, it can be hypothesized that a reduction of the PI of the fetal renal artery by maternal hydration may represent an increase in fetal renal perfusion, presumably an increase in fetal urine production. However, at least in our study, PI did not show a significant change in any of the groups. In fact, changes in PI evaluated at preglomerular regions of the fetal renal artery may not reflect the amount of water filtered in the glomerulus.
References 1. Goodlin RC, Anderson JC, Gallagher TF. Relationship between amniotic fluid volume and maternal plasma volume expansion. Am J Obstet Gynecol 1983;146:505–11. 2. Sciscione AC, Costigan KA, Johnson TRB. Increase in ambient temperature may explain decrease in amniotic fluid index. Am J Perinatol 1997;14:249 –51. 3. Kilpatrick SJ, Safford KL, Pomeroy T, Hoedt L, Scheerer L, Laros RK. Maternal hydration increases amniotic fluid index. Obstet Gynecol 1991;78:1098 –102. 4. Flack NJ, Sepulvada W, Bower S, Fisk NM. Acute maternal hydration in third-trimester oligohydramnios: Effects on amniotic fluid volume, uteroplacental perfusion, and fetal blood flow and urine output. Am J Obstet Gynecol 1995;173:1186 –91. 5. Ross MG, Cedars L, Nijland MJM, Ogundipe A. Treatment of oligohydramnios with maternal 1-deamino-[8-d-arginine] vasopressin-induced plasma hypoosmolality. Am J Obstet Gynecol 1996;174:1608 –13. 6. Sherer DM, Cullen JBH, Thompson HO, Woods JR Jr. Transient oligohydramnios in a severely hypovolemic gravid woman at 35 weeks’ gestation, with fluid reaccumulating immediately after intravenous maternal hydration. Am J Obstet Gynecol 1990;162: 770 –1. 7. Chelmow D, Baker ER, Jones L. Maternal intravenous hydration and amniotic fluid index in patients with preterm ruptured membranes. J Soc Gynecol Investig 1996;3:127–30. 8. Powers DR, Brace RA. Fetal cardiovascular and fluid responses to maternal volume loading with lactated Ringer’s or hypotonic solution. Am J Obstet Gynecol 1991;165:1504 –15. 9. Hurley JK, Kirkpatrick SE, Pitlick PT, Friedman WF, Mendosa SA. Renal responses of the fetal lamb to fetal or maternal volume expansion. Circ Res 1977;40:557– 60. 10. Phelan JP, Smith CV, Broussard P, Small M. Amniotic fluid volume assessment with the four-quadrant technique at 36-42 weeks’ gestation. J Reprod Med 1987;32:540 –2. 11. Gauer OH, Seiker HD. The continuous recording of central venous pressure from an arm vein. Circ Res 1956;4:74 – 8. 12. Gosling RG, King DH. Ultrasound angiology. In: Marcus AW,
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13. 14.
15.
16.
17.
18.
19.
20.
Adamson L, eds. Arteries and veins. New York: Churchill Livingstone, 1975:61–98. Nishida H, Sakanoue M, Kurachi K, Asada A, Kubo S, Funakawa H. Fetal growth curve of Japanese. Acta Neonat Jpn 1984;20:90 –7. Faber JJ, Anderson DF. Model study of placental water transfer and causes of fetal water disease in sheep. Am J Physiol 1990;258: R1257–70. Nijland MJM, Ross MG, Kullama LK, Bradley K, Ervin MG. DDAVP-induced maternal hypoosmolality increases ovine fetal urine flow. Am J Physiol 1995;268:R358 – 65. Nisell H, Carlstrom K, Cizinsky S, Grunewald C, Nylund L, Randmaa I. Atrial natriuretic peptide concentrations and hemodynamic effects of acute plasma volume expansion in normal pregnancy and preeclampsia. Obstet Gynecol 1992;79:902–7. Ross MG, Nijland MJM, Kullama LK. 1-Deamino-[8-d-arginine] vasopressin-induced maternal plasma hypoosmolality increases ovine amniotic fluid volume. Am J Obstet Gynecol 1996;174:1118 – 27. Veile JC, Penry M, Mueller-Heubach E. Fetal renal pulsed Doppler waveform in prolonged pregnancies. Am J Obstet Gynecol 1993; 169:882– 4. Mari G, Kirshon B, Abuhamad A. Fetal renal artery flow velocity waveforms in normal pregnancies and pregnancies complicated by polyhydramnios and oligohydramnios. Obstet Gynecol 1993;81: 560 – 4. Mitra SC, Ganesh V, Apuzzio JJ. Fetal renal artery and umbilical
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artery Doppler flow and fetal urine output. Am J Perinatol 1995;12:11–3. 21. Yasuhi I, Hirai M, Ishimaru T, Yamabe T. Change in fetal urine production rate in growth-retarded fetuses after maternal meal ingestion. Obstet Gynecol 1996;88:833–7.
Address reprint requests to:
Shigeharu Doi, MD Department of Obstetrics and Gynecology Chiba University School of Medicine 1-8-1 Inohana, Chuo-ku, Chiba City Chiba 260 Japan E-mail: [email protected]
Received January 20, 1998. Received in revised form May 1, 1998. Accepted May 7, 1998.
Copyright © 1998 by The American College of Obstetricians and Gynecologists. Published by Elsevier Science Inc.
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Oligohydramnios is a common phenomenon in postterm pregnancy and fetal growth restriction (FGR), and etiologies of reduced amniotic fluid (AF) volume may include maternal intravascular fluid depletion1 and even insensible fluid loss.2 Maternal hydration has been From the Department of Obstetrics and Gynecology, Chiba University School of Medicine, Chiba, Japan.
VOL. 92, NO. 4, PART 1, OCTOBER 1998
the focus recently of studies in women with oligohydramnios,1,3– 6 with the expectation of an increase in AF volume. The mode of administration that received the most attention in these studies was oral hydration, achieving a reduction of maternal plasma osmolality and a significant increase in amniotic fluid index (AFI).3–5 An alternative route of maternal hydration is intravenous (IV) fluid loading, which was attempted as a method of volume expansion in women who were dehydrated or hypovolemic, and this corrected oligohydramnios as well as maternal plasma volume.1,6 Importantly, AF volume has been reported to correlate with maternal plasma volume.1 Although one randomized study in women showed the benefit of IV hydration with isotonic fluid for increasing AFI,7 the effect of IV route on AF volume is still controversial. In ovine studies, isotonic maternal volume expansion through the IV route did not increase fetal urine production,8,9 which is thought to be the most important contributor to AF volume in the third trimester; however, hypotonic volume expansion increased fetal urine production.8 No reported studies in women have compared the effects of oral and IV routes of administration on AF volume. This investigation, therefore, was designed as a randomized and blinded study to compare the effects of maternal hydration with oral water, IV isotonic fluid, and IV hypotonic fluid on AF volume in women with oligohydramnios and to evaluate the processes involved in increasing AF volume.
Materials and Methods Patients with ultrasonographic diagnosis of oligohydramnios were evaluated for participation in a randomized trial after admission for induction of labor at the Division of Obstetrics and Gynecology of Chiba Uni-
0029-7844/98/$19.00 PII S0029-7844(98)00242-7
525
versity Hospital, Chiba, Japan. Oligohydramnios was diagnosed as an AFI of less than or equal to 5.0 cm of four-quadrant ultrasonographic measurement.10 This study was approved by the Chiba University Hospital Ethics Committee. The subjects met the following criteria: singleton pregnancy; well-established gestational age over 35 weeks; intact membranes; no maternal complications, such as hypertension, cardiovascular disease, hyperthyroidism, and diabetes; no evidence of preeclampsia; no fetal structural malformation; and no evidence of fetal distress on nonstress test. After obtaining written informed consent, prospective randomization was carried out by sealed-card selection into four groups as follows: 1) IV infusion of 2 L/2 h lactated Ringer’s solution as an isotonic fluid (255 mOsm/kg/H2O); 2) IV infusion of 2 L/2 h hypotonic fluid made of diluted Ringer’s solution (150 mOsm/kg/H2O); 3) oral intake of 2 L/2 h water; and 4) control group receiving a fixed slow drip for maintenance of venous route. Overhydration with acute IV infusion may elicit adverse effects such as cardiac failure and/or pulmonary edema. Therefore, we monitored serially maternal electrocardiogram (ECG), blood pressure (BP), respiratory rates, and peripheral venous pressure through an indwelling 18-gauge catheter in the antecubital vein for prevention of maternal side effects in the IV infusion groups. Changes in peripheral venous pressure have been shown to be related closely to changes in central venous pressure.11 Maternal plasma osmolality, serum sodium level, hematocrit, and hemoglobin concentration were measured before and at the end of hydration by the usual laboratory techniques. In the IV hypotonic group, we measured plasma electrolytes at least once during hydration to prevent potential hyponatremia and extensive hemolysis from occurring. All measurements of AFI and Doppler studies were performed with a 3.5-MHz transducer with pulse-wave color Doppler ultrasonography (Aloka SSD-2000, Tokyo, Japan) before hydration and at 1 hour after hydration by one ultrasonographer who was blinded to the randomization of the study groups. Measurement of AFI was performed twice on each occasion, and mean AFI was obtained by averaging the two measurements. Patients were excluded from enrollment to the study when AFI was found to be greater than 6.0 cm. The fetal renal artery was visualized as a branch from the descending aorta into the hilum of the kidney in the longitudinal view of the fetal body with color flow mapping. Velocity waveforms were recorded in the state of absent fetal breathing movements. The pulsatility index12 (PI) was calculated (PI 5 [systolic velocity -
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Table 1. Patient Characteristics
Characteristic
IV isotonic (n 5 21)
IV hypotonic (n 5 21)
Oral water (n 5 21)
Control (n 5 21)
Maternal age 28.1 (23–33) 26.3 (26 –34) 29.3 (25–35) 28.6 (22–32) (y) Parity (n) 1.3 (0 –2) 1.5 (0 –3) 1.5 (0 –2) 1.6 (0 –3) Gestational age 39.5 (35– 41) 39.7 (35– 42) 37.3 (36 – 42) 38.9 (35– 42) at study (wk) Gestational age 8 10 11 8 .41 wk (n) SGA at 4 4 6 5 delivery (n) IV 5 intravenous; SGA 5 small for gestational age.13 Data are presented as mean (range) or n.
diastolic velocity] / mean velocity), with three consecutive waveforms as renal artery resistance. The sample size was determined from our data of a preliminary study of AFI measurements in 30 cases of oligohydramnios (3.6 6 1.5 cm, mean 6 standard deviation). The initial oral hydration study by Kilpatrick et al3 demonstrated a 1.5-cm increase in AFI in women with oligohydramnios. Therefore, a power calculation indicated that approximately 20 subjects per group would be required to have 90% of power at one-sided a of .05 to detect at least a 1.5-cm increase in AFI. Eighty-four women with oligohydramnios, divided into four groups, were enrolled finally in this study. Characteristics of the patients are listed in Table 1. Maternal age, gestational age, parity, rate of FGR,13 and postterm pregnancy were similar among all groups. Data were compared by paired t test within each group. The differences of the values between prehydration and posthydration were presented as D and compared between the groups with analysis of variance followed by Fisher protected least significance difference. Linear regression analysis was performed for the correlation between D AFI and D osmolality. P , .05 was considered statistically significant.
Results There were no changes in maternal ECG, BP, and peripheral venous pressure during hydration, and no patients discontinued the study because of adverse effects. Table 2 presents the values of AFI, maternal plasma osmolality, hematocrit, and hemoglobin concentration. There were no differences in AFI, maternal osmolality, hematocrit, and hemoglobin concentration before hydration among the groups. One hour after hydration, D AFI was significantly greater in the IV
Obstetrics & Gynecology
Table 2. Changes in Amniotic Fluid Volume, Maternal Osmolality, Hematocrit, and Hemoglobin Concentration Before and After Hydration IV isotonic (n 5 21) AFI Before Change in AFI Osmolality Before Change in osmolality Hct Before After P Hb Before After P
IV hypotonic (n 5 21)
Oral water (n 5 21)
Control (n 5 21)
3.5 6 1.5 0.5 6 1.1
3.6 6 1.3 2.8 6 1.9*
3.4 6 1.5 3.8 6 1.9*
3.2 6 1.3 0.5 6 1.1
285.6 6 2.8 20.5 6 1.2
286.1 6 3.8 26.9 6 3.5*
285.1 6 3.3 28.0 6 3.8*
286.2 6 2.4 20.4 6 1.3
32.0 6 2.9 29.5 6 2.3 ,.001
31.5 6 3.2 32.2 6 3.2 NS
31.7 6 2.9 32.5 6 3.1 NS
31.0 6 3.4 31.3 6 3.1 NS
11.0 6 1.6 10.1 6 1.4 ,.001
11.2 6 1.9 11.3 6 2.0 NS
11.1 6 1.5 11.3 6 1.7 NS
10.8 6 1.3 10.9 6 1.3 NS
IV 5 intravenous; AFI 5 amniotic fluid index; Hct 5 hematocrit; P 5 significance by paired t test; NS 5 no significance; Hb 5 hemoglobin concentration. Data are presented as mean 6 standard deviation. * P , .001 includes both compared with IV isotonic group and compared with control group by analysis of variance followed by Fisher protected least significance difference.
hypotonic and oral water groups (2.8 6 1.9, P , .001; 3.8 6 1.9, P , .001, respectively) than in the control group (0.5 6 1.1), but not in the IV isotonic group (0.5 6 1.1). Similarly, D osmolality also was significantly greater in the IV hypotonic and oral water groups (2 6.9 6 3.5, P , .001; 2 8.0 6 3.8, P , .001, respectively) than in the control group (2 0.4 6 1.3), but was not higher in the IV isotonic group (2 0.5 6 1.2). On the other hand, significant decreases of maternal hematocrit and hemoglobin concentration were found only after IV isotonic hydration (32.0 6 2.9 to 29.5 6 2.3, P , .001; 11.0 6 1.6 to 10.1 6 1.4, P , .001, respectively). There was a significant correlation between D AFI and D osmolality in both IV hypotonic (r 5 .58, P , .001) and oral water groups (r 5 .63, P , .001) (Figure 1). Maternal serum sodium levels also decreased significantly after hydration in the IV hypotonic and oral water groups (138.5 6 2.0 to 130.8 6 3.8, P , .01; 139.6 6 2.4 to 130.2 6 2.5, P , .001, respectively), but not in the IV isotonic and control groups (137.2 6 1.8 to 138.4 6 3.5, not significant; 137.0 6 2.5 to 136.8 6 3.5, not significant). Table 3 demonstrates the differences between the PI values of the fetal renal artery before and after hydration in each group. No significant differences were observed among the groups.
However, with regard to oral hydration, our results showed a similar effect as in other reported studies3,4; we demonstrated that IV hydration with hypotonic fluid was equally effective for increasing the AFI. The changes in AFI correlated significantly with changes in maternal osmolality. The results suggest that maternal plasma osmotic change has a more profound impact on acute increase of AF volume when compared with maternal volume expansion through the IV route.
Discussion Our randomized study demonstrated that in women with oligohydramnios, a significant increase in the AFI was achieved by both IV hypotonic fluid loading and oral hydration, but not by IV isotonic fluid loading.
VOL. 92, NO. 4, PART 1, OCTOBER 1998
Figure 1. Correlation between maternal osmotic change and changes in amniotic fluid index (AFI). The solid line represents the linear regression line of the oral water group (closed circles), and the dashed line represents that of the intravenous hypotonic fluid group (open circles). Osm 5 osmolality.
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Table 3. Difference in Fetal Renal Artery Pulsatility Index Before and After Hydration Renal artery
IV isotonic
IV hypotonic
Oral water
Control
Change in PI* 20.05 6 0.42 20.07 6 0.51 0.05 6 0.57 20.06 6 0.66 (n 5 16) PI 5 pulsatility index. Data are presented as mean 6 standard deviation. P values were not significant between the groups by analysis of variance followed by Fisher protected least significance difference. * Posthydration value minus prehydration value.
Goodlin et al1 showed that vigorous IV fluid loading improved the maternal “dehydrated” state, as evidenced by the decrease in both hematocrit and plasma osmolality, resulting in an increase in AF volume. In the present study, apparently “dehydrated” and “hypovolemic” women with higher plasma osmolality were not included in any of the groups. Therefore, it seems unlikely that in the IV isotonic group, maternal osmolality changes significantly in “nondehydrated” women. With respect to the physiologic principles, water transfer between mother and fetus is regulated dominantly by osmotic forces, in which electrolyte gradients determine net transplacental water exchange.14 In a recent ovine study with maternal oral water loading,15 it also was reported that a reduction of maternal fetal osmotic gradient facilitated water transfer to the fetus, leading to an increase in fetal urine production. Thus, taken together with our results, it is unlikely that acute maternal volume expansion achieves fluid shift into the fetus without maternal osmotic change. Of interest was the fact that the IV isotonic group alone showed a significant decrease in both hematocrit and hemoglobin concentration. The decrease in hemoglobin concentration may reflect the maternal plasma volume expansion in the IV isotonic group.16 It is uncertain whether plasma volume expansion failed to occur in the IV hypotonic and oral water groups. Alternatively, the lack of change in hemoglobin concentration in these groups may be explained in part by water transfer from the mother into the fetus. In contrast to our results, Chelmow et al7 found a significant increase of 5 cm in AFI in patients with premature ruptured membranes after infusion of 1L IV isotonic fluid. The reason for this conflicting finding is unclear, because the magnitudes of maternal osmotic change and plasma volume expansion were not evaluated in their study. The main source of the increase in AFI with hydration has not been identified. Flack et al4 reported that fetal urine production did not change significantly with maternal oral hydration in women with oligohydram-
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nios, as determined by ultrasonographic estimation of hourly fetal urine flow. On the other hand, recent ovine studies have demonstrated that maternal water loading with the administration of IV arginine vasopressin agonist increased fetal urine production15,17 and decreased fetal swallowing activity, resulting in a marked increase in AF volume.17 In the human fetus, Doppler velocity waveform indices of the fetal renal artery have been used to represent an indirect method for evaluation of fetal renal perfusion, and the correlations between fetal renal artery resistance and AF volume, and fetal urine production also have been investigated.18 –21 Thus, it can be hypothesized that a reduction of the PI of the fetal renal artery by maternal hydration may represent an increase in fetal renal perfusion, presumably an increase in fetal urine production. However, at least in our study, PI did not show a significant change in any of the groups. In fact, changes in PI evaluated at preglomerular regions of the fetal renal artery may not reflect the amount of water filtered in the glomerulus.
References 1. Goodlin RC, Anderson JC, Gallagher TF. Relationship between amniotic fluid volume and maternal plasma volume expansion. Am J Obstet Gynecol 1983;146:505–11. 2. Sciscione AC, Costigan KA, Johnson TRB. Increase in ambient temperature may explain decrease in amniotic fluid index. Am J Perinatol 1997;14:249 –51. 3. Kilpatrick SJ, Safford KL, Pomeroy T, Hoedt L, Scheerer L, Laros RK. Maternal hydration increases amniotic fluid index. Obstet Gynecol 1991;78:1098 –102. 4. Flack NJ, Sepulvada W, Bower S, Fisk NM. Acute maternal hydration in third-trimester oligohydramnios: Effects on amniotic fluid volume, uteroplacental perfusion, and fetal blood flow and urine output. Am J Obstet Gynecol 1995;173:1186 –91. 5. Ross MG, Cedars L, Nijland MJM, Ogundipe A. Treatment of oligohydramnios with maternal 1-deamino-[8-d-arginine] vasopressin-induced plasma hypoosmolality. Am J Obstet Gynecol 1996;174:1608 –13. 6. Sherer DM, Cullen JBH, Thompson HO, Woods JR Jr. Transient oligohydramnios in a severely hypovolemic gravid woman at 35 weeks’ gestation, with fluid reaccumulating immediately after intravenous maternal hydration. Am J Obstet Gynecol 1990;162: 770 –1. 7. Chelmow D, Baker ER, Jones L. Maternal intravenous hydration and amniotic fluid index in patients with preterm ruptured membranes. J Soc Gynecol Investig 1996;3:127–30. 8. Powers DR, Brace RA. Fetal cardiovascular and fluid responses to maternal volume loading with lactated Ringer’s or hypotonic solution. Am J Obstet Gynecol 1991;165:1504 –15. 9. Hurley JK, Kirkpatrick SE, Pitlick PT, Friedman WF, Mendosa SA. Renal responses of the fetal lamb to fetal or maternal volume expansion. Circ Res 1977;40:557– 60. 10. Phelan JP, Smith CV, Broussard P, Small M. Amniotic fluid volume assessment with the four-quadrant technique at 36-42 weeks’ gestation. J Reprod Med 1987;32:540 –2. 11. Gauer OH, Seiker HD. The continuous recording of central venous pressure from an arm vein. Circ Res 1956;4:74 – 8. 12. Gosling RG, King DH. Ultrasound angiology. In: Marcus AW,
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Adamson L, eds. Arteries and veins. New York: Churchill Livingstone, 1975:61–98. Nishida H, Sakanoue M, Kurachi K, Asada A, Kubo S, Funakawa H. Fetal growth curve of Japanese. Acta Neonat Jpn 1984;20:90 –7. Faber JJ, Anderson DF. Model study of placental water transfer and causes of fetal water disease in sheep. Am J Physiol 1990;258: R1257–70. Nijland MJM, Ross MG, Kullama LK, Bradley K, Ervin MG. DDAVP-induced maternal hypoosmolality increases ovine fetal urine flow. Am J Physiol 1995;268:R358 – 65. Nisell H, Carlstrom K, Cizinsky S, Grunewald C, Nylund L, Randmaa I. Atrial natriuretic peptide concentrations and hemodynamic effects of acute plasma volume expansion in normal pregnancy and preeclampsia. Obstet Gynecol 1992;79:902–7. Ross MG, Nijland MJM, Kullama LK. 1-Deamino-[8-d-arginine] vasopressin-induced maternal plasma hypoosmolality increases ovine amniotic fluid volume. Am J Obstet Gynecol 1996;174:1118 – 27. Veile JC, Penry M, Mueller-Heubach E. Fetal renal pulsed Doppler waveform in prolonged pregnancies. Am J Obstet Gynecol 1993; 169:882– 4. Mari G, Kirshon B, Abuhamad A. Fetal renal artery flow velocity waveforms in normal pregnancies and pregnancies complicated by polyhydramnios and oligohydramnios. Obstet Gynecol 1993;81: 560 – 4. Mitra SC, Ganesh V, Apuzzio JJ. Fetal renal artery and umbilical
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artery Doppler flow and fetal urine output. Am J Perinatol 1995;12:11–3. 21. Yasuhi I, Hirai M, Ishimaru T, Yamabe T. Change in fetal urine production rate in growth-retarded fetuses after maternal meal ingestion. Obstet Gynecol 1996;88:833–7.
Address reprint requests to:
Shigeharu Doi, MD Department of Obstetrics and Gynecology Chiba University School of Medicine 1-8-1 Inohana, Chuo-ku, Chiba City Chiba 260 Japan E-mail: [email protected]
Received January 20, 1998. Received in revised form May 1, 1998. Accepted May 7, 1998.
Copyright © 1998 by The American College of Obstetricians and Gynecologists. Published by Elsevier Science Inc.
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