Clinical Articles A prospective randomized study of saline solution amnioinfusion John Owen, MD, Brenda V. Henson, RN, and John C. Hauth, MD Birmingham, Alabama We performed a prospective randomized study of saline solution amnioinfusion in four types of pregnancy complications: postterm pregnancy, variable decelerations in labor, preterm labor, and oligohydramnios-suspected growth retardation. A total of 100 patients were randomized, 43 to undergo amnioinfusion and 57 to be in a control group. Patients undergoing amnioinfusion had a significantly decreased incidence of postpartum endometritis (2.4% vs 19%, P = 0.01) and a lower incidence of cesarean delivery that was due to fetal distress in labor (4.7% vs 16%, P = 0.07). The use of amnioinfusion also made a significant contribution to the four-quadrant ultrasonographic estimate of amniotic fluid volume (14.7 vs 9.8 cm, p < 0.001). All other maternal and neonatal outcome parameters were similar between the two groups. We conclude that saline solution amnioinfusion in labor may be a beneficial procedure but that further stUdies are needed. (AM J DeSTET GVNECOL 1990;162:1146-9.)
Key words: Saline solution amnioinfusion, fetal distress, postpartum infection The use of saline solution amnioinfusion has been reported to be of value in patients with preterm premature rupture of the membranes l and recurrent variable decelerations in labor!' 3 To further define its role in obstetrics, we undertook a prospective randomized study of amnioinfusion in women with four types of pregnancy complications: postterm pregnancy, variable decelerations in labor, pre term labor with ruptured amniotic membranes, and oligohydramnios-suspected growth retardation. We postulated that the use of amnioinfusion in patients with these obstetric complications would decrease the incidence of operative vaginal or cesarean delivery, or both, as a result of fetal distress in labor.
Material and methods Patients came to the labor suite at the University of Alabama Hospital and were evaluated by one of the authors for inclusion criteria. Patients who were considered eligible and who consented to the study were randomly assigned to either amnioinfusion or control From the Department of Obstetrics and Gynecology, The University of Alabama at Birmingham. Received for publication October 27, 1989; revised January 24, 1990; accepted February 6, 1990. Reprint requests: John Owen, MD, Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, AL 35294. 611 /20024
1146
groups and in relation to the following criteria. For the postdate pregnancy group, patients must have completed at least 42 weeks' gestation. All patients had excellent gestational dates, including an early ultrasonographic examination. Patients either were in spontaneous labor or were seen for an indicated induction of labor, and none of them had a prior positive fetal heart rate contraction stress test. For the group with variable decelerations in labor, patients must have had recurrent mild to moderate variable decelerations that did not respond to maternal position change, hydration, and oxygen therapy. Patients also were eligible if they had intermittent episodes of baseline bradycardia that were not judged severe enough to warrant immediate delivery. In the group with preterm labor, those included were in labor before 37 weeks' gestation. In the oligohydramnios-suspected growth retardation group, patients were between 37 and 42 weeks' gestation with an admisison diagnosis of oligohydramnios and/ or suspected fetal growth retardation. After each patient was assigned to one of the four complication groups, the randomization to receive amnioinfusion or to serve as a control was performed by using sealed envelopes. We did not collect data on the few patients who were eligible but who refused participation in the study. In summary, the groups with postterm pregnancies, preterm labor, and oligohydramnios-suspected growth retardation were considered to be at increased
Saline amnioinfusion in labor
Volume 162 Number 5
risk for significant cord compression and received amnioinfusion as a prophylactic measure. Only those patients with variable decelerations of the fetal heart rate received amnioinfusion as a treatment of the existing non reassuring fetal heart rate patterns. Thereafter an intrauterine pressure catheter was placed for direct monitoring of the labor pattern, and a four-quadrant assessment of amniotic fluid volume was performed.' Randomization was performed by drawing the randomly generated group assignments from a sealed envelope. All randomized patients were included in the data analyses. If amnioinfusion was chosen, a second pressure catheter was introduced through which the saline solution was infused. The decisions of when to place the pressure catheter and how to manage the remainder of each patient's labor and delivery were made by the resident staff in consultation with an attending physician. Normal saline solution was warmed to 37° C and infused with an IMED pump. The infusion rate was 10 mUmin for 60 minutes and then 3 mUmin until delivery. After the initial 600 ml had been infused, each patient underwent a second four-quadrant ultrasonographic determination of amniotic fluid volume. The ultrasonographic examinations and saline solution infusions were performed by one of the authors (B. V. H.). The cervical dilatation at the time of randomization, the total volume of saline solution infused, and the labor curve from randomization until delivery were recorded prospectively. The study patients, as well as the nurses and physicians in the labor suite, were not blinded to the randomized assignments. Exclusion criteria included multiple gestation, nonvertex presentation, amnionitis, vaginal bleeding, a fetal heart rate baseline or pattern severe enough to warrant immediate delivery, known fetal anomalies, and significant maternal disease states such as severe pregnancy-induced hypertension or insulin-dependent diabetes mellitus. The presence of meconium staining of the amniotic fluid, a prior low transverse cesarean section, or the need for oxytocin induction or augmentation of labor were not considered contraindications. During the study period, all fetuses had continuous internal electronic monitoring of the heart rate. The diagnosis of fetal distress was made by the resident staff in consultation with the attending physician, and all operative deliveries were determined to be indicated by the attending physician. Whenever possible, arterial and venous cord blood gas determinations were obtained on each neonate. There were no restrictions to the use of conduction anesthesia because of the amnioinfusion protocol. Postpartum evaluations were performed by the resident staff, and standard definitions of postoperative febrile morbidity and endometritis
1147
were used. Data were analyzed by X2 test, Fisher's exact test, and the Student t test where appropriate. If the probability of a type I error was ~0.05, the result was considered significant. Results
A total of 100 patients were randomized; 43 received amnioinfusion and 57 served as controls. Table I depicts the risk group assignments for the treatment and control populations. A comparison of demographic and obstetric characteristics is listed in Table II. There were no significant differences between the two study populations except that the estimated gestational age of patients with oligohydramnios/suspected growth retardation in the amnioinfusion group was significantly less that that of the control group (p = 0.05). In 31 of the 43 patients receiving treatment the initial 600 ml infusion was completed and the second amniotic fluid volume estimate was performed according to the protocol. However, 10 patients were delivered of their infants before the loading volume had been infused. In the remaining two patients the postinfusion ultrasonographic examination was not accomplished. In these 31 patients the mean amniotic fluid volume increased from 9.8 ± 3.8 to 14.7 ± 3.7 cm after infusion of the loading 600 ml of saline solution (p < 0.001). Maternal and neonatal outcome data are listed in Table III. For all but one of the outcome parameters studied, there was no significant difference between the treatment and control groups although a trend toward a decreased incidence of cesarean delivery because of fetal distress was noted in the amnioinfusion patients (4.7% vs 16%, P = 0.07, one-tailed). As has been previously reported,' we sought to determine the effects of parity on the incidence of cesarean delivery because of fetal distress between the amnioinfusion and control groups. However, unlike Miyazaki and Nevarez,' who found that amnioinfusion was more beneficial in primiparous women, we found in multiparous patients that the incidence of cesarean delivery because of fetal distress was 0% (0 of 22) in the amnioinfusion group versus 22% (8 of 36) in the control group (p = 0.02). A similar benefit was not seen in the primiparous patients (p = 1.0). An unexpected finding was a decreased incidence of postpartum endometritis in the amnioinfusion patients (2.4% vs 19%, P = 0.01). This difference could not be explained on the basis of a difference in the incidence of positive maternal group B streptococcal cultures of the cervix. Comment
The theoretical basis for amnioinfusion is that it reduces umbilical cord compression and variable fetal heart rate decelerations, a common cause of fetal dis-
1148 Owen, Henson, and Hauth
May 1990 Am J Obstet Gynecol
Table I. Study group assignments for amnioinfusion and control Category
P=
A mnioinfusion
Control
Total
Postterm pregnancy Variable decelerations in labor Pre term labor Oligohydramnios-growth retardation
5 13 II 14
6 20 18 13
11 33 29 27
TOTAL
43
57
100
0.71.
Table II. Demographic variables of amnioinfusion and control groups Treatment
Initial 4-quadrant AFV* (cm) Cervical examination randomization (cm) Gestational age (wk) Postterl!l (n = 11) Decelerations (n = 33) Preterm labor (n = 28) Oligo/IUGR (n = 26) Meconium-stained fluid Primiparous Birth weight (gm) Nonwhite Maternal age (yr) Epidural anesthesia Labor abnormality Oxytocin used Nuchal cord
Control
(N = 43)
(N = 57)
p
9.2 ± 3.7 3.7 ± 1.4
8.4 ± 3.1 3.6 ± 1.9
0.22 0.63
43 ± 0.33 40 ± 0.65 34 ± 1.8 40 ± 1.7 II (26%) 21 (49%) 2894 ± 657 29 (67%) 23 ± 5.0 29 (67%) 17 (40%) 32 (74%) 13 (30%)
43 ± 0.46 39 ± 2.6 34 ± 1.7 41 ± 1.6 19 (33%) 21 (37%) 2951 ± 755 39 (71 %) 23 ± 5.4 38 (67%) 28 (49%) 36 (63%) 18 (32%)
0.60 0.43 0.99 0.05 0.40 0.23 0.69 0.92 0.70 0.94 0.34 0.23 0.89
Test
AFV, Amniotic fluid volume; Oligo, oligohydramnios; [VCR, intrauterine growth retardation.
*Initial ultrasonographic examination not performed in four cases.
tress. 5 Since an unknown quantity of instilled fluid may leak out during the therapy, to date it has not been known how much is actually retained. Our results using a four-quadrant estimate show that amnioinfusion makes a significant impact on the amniotic fluid volume. Miyazaki and Nevarez' reported that variable decelerations in labor were ameliorated in 51 % of patients who received amnioinfusion versus only 4.2% of the control group and further noted that the effects of amnioinfusion were more pronounced in the primiparous group than in multiparous patients. Their series contained 48 nulliparous patients, and in this population the incidence of cesarean delivery because of fetal distress was 15% in the amnioinfusion group versus 48% in the control group (p = 0.03). Nageotte et al. l also reported that amnioinfusion had a significant impact on the incidence of variable decelerations in labor in patients with preterm premature rupture of the membranes; they also noted, as we have, a trend toward a decreased incidence of cesarean delivery because of fetal distress in the amnioinfusion group as compared with the control group (0.05 < P < 0.10). With optimal labor management, one would not ex-
pect a technique such as amnioinfusion to improve the immediate neonatal outcome, although Nageotte et al. l reported a significantly lower umbilical cord arterial pH in 32 control subjects compared with 29 amnioinfusion patients. However, as our results indicate, the incidence of cesarean delivery because of fetal distress was reduced in the treatment group, although the reduction did not reach statistical significance except in the multiparous patients. This is likely a result of our sample size since it would require 200 patients in each group to be 80% certain of detecting a 50% reduction in the rate of cesarean section because of fetal distress (from 16%, as in our control group, to 8%, one-tailed, a = 0.05). If a 25% reduction is considered clinically significant, then 910 patients in each group would be required. Nevertheless, the power of this study to detect a threefold difference in the incidence of cesarean delivery because of fetal distress (16% vs 4.7%), if this difference actually exists, is 0.99. Furthermore, we could demonstrate no harmful effects from either the placement of a second intrauterine pressure catheter or the saline solution amnioinfusion. In fact the maternal infection rate was significantly lower in the treatment group. This might be secondary
Saline amnioinfusion in labor
Volume 162 Number 5
1149
Table III. Maternal and neonatal outcome variables for amnioinfusion and control groups Treatment = 43)
(N
Operative delivery because of fetal distress Cesarean delivery Indicated operative vaginal delivery Total Total cesarean deliveries Postpartum endometritis Cord arterial pH
Key words: Saline solution amnioinfusion, fetal distress, postpartum infection The use of saline solution amnioinfusion has been reported to be of value in patients with preterm premature rupture of the membranes l and recurrent variable decelerations in labor!' 3 To further define its role in obstetrics, we undertook a prospective randomized study of amnioinfusion in women with four types of pregnancy complications: postterm pregnancy, variable decelerations in labor, pre term labor with ruptured amniotic membranes, and oligohydramnios-suspected growth retardation. We postulated that the use of amnioinfusion in patients with these obstetric complications would decrease the incidence of operative vaginal or cesarean delivery, or both, as a result of fetal distress in labor.
Material and methods Patients came to the labor suite at the University of Alabama Hospital and were evaluated by one of the authors for inclusion criteria. Patients who were considered eligible and who consented to the study were randomly assigned to either amnioinfusion or control From the Department of Obstetrics and Gynecology, The University of Alabama at Birmingham. Received for publication October 27, 1989; revised January 24, 1990; accepted February 6, 1990. Reprint requests: John Owen, MD, Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, AL 35294. 611 /20024
1146
groups and in relation to the following criteria. For the postdate pregnancy group, patients must have completed at least 42 weeks' gestation. All patients had excellent gestational dates, including an early ultrasonographic examination. Patients either were in spontaneous labor or were seen for an indicated induction of labor, and none of them had a prior positive fetal heart rate contraction stress test. For the group with variable decelerations in labor, patients must have had recurrent mild to moderate variable decelerations that did not respond to maternal position change, hydration, and oxygen therapy. Patients also were eligible if they had intermittent episodes of baseline bradycardia that were not judged severe enough to warrant immediate delivery. In the group with preterm labor, those included were in labor before 37 weeks' gestation. In the oligohydramnios-suspected growth retardation group, patients were between 37 and 42 weeks' gestation with an admisison diagnosis of oligohydramnios and/ or suspected fetal growth retardation. After each patient was assigned to one of the four complication groups, the randomization to receive amnioinfusion or to serve as a control was performed by using sealed envelopes. We did not collect data on the few patients who were eligible but who refused participation in the study. In summary, the groups with postterm pregnancies, preterm labor, and oligohydramnios-suspected growth retardation were considered to be at increased
Saline amnioinfusion in labor
Volume 162 Number 5
risk for significant cord compression and received amnioinfusion as a prophylactic measure. Only those patients with variable decelerations of the fetal heart rate received amnioinfusion as a treatment of the existing non reassuring fetal heart rate patterns. Thereafter an intrauterine pressure catheter was placed for direct monitoring of the labor pattern, and a four-quadrant assessment of amniotic fluid volume was performed.' Randomization was performed by drawing the randomly generated group assignments from a sealed envelope. All randomized patients were included in the data analyses. If amnioinfusion was chosen, a second pressure catheter was introduced through which the saline solution was infused. The decisions of when to place the pressure catheter and how to manage the remainder of each patient's labor and delivery were made by the resident staff in consultation with an attending physician. Normal saline solution was warmed to 37° C and infused with an IMED pump. The infusion rate was 10 mUmin for 60 minutes and then 3 mUmin until delivery. After the initial 600 ml had been infused, each patient underwent a second four-quadrant ultrasonographic determination of amniotic fluid volume. The ultrasonographic examinations and saline solution infusions were performed by one of the authors (B. V. H.). The cervical dilatation at the time of randomization, the total volume of saline solution infused, and the labor curve from randomization until delivery were recorded prospectively. The study patients, as well as the nurses and physicians in the labor suite, were not blinded to the randomized assignments. Exclusion criteria included multiple gestation, nonvertex presentation, amnionitis, vaginal bleeding, a fetal heart rate baseline or pattern severe enough to warrant immediate delivery, known fetal anomalies, and significant maternal disease states such as severe pregnancy-induced hypertension or insulin-dependent diabetes mellitus. The presence of meconium staining of the amniotic fluid, a prior low transverse cesarean section, or the need for oxytocin induction or augmentation of labor were not considered contraindications. During the study period, all fetuses had continuous internal electronic monitoring of the heart rate. The diagnosis of fetal distress was made by the resident staff in consultation with the attending physician, and all operative deliveries were determined to be indicated by the attending physician. Whenever possible, arterial and venous cord blood gas determinations were obtained on each neonate. There were no restrictions to the use of conduction anesthesia because of the amnioinfusion protocol. Postpartum evaluations were performed by the resident staff, and standard definitions of postoperative febrile morbidity and endometritis
1147
were used. Data were analyzed by X2 test, Fisher's exact test, and the Student t test where appropriate. If the probability of a type I error was ~0.05, the result was considered significant. Results
A total of 100 patients were randomized; 43 received amnioinfusion and 57 served as controls. Table I depicts the risk group assignments for the treatment and control populations. A comparison of demographic and obstetric characteristics is listed in Table II. There were no significant differences between the two study populations except that the estimated gestational age of patients with oligohydramnios/suspected growth retardation in the amnioinfusion group was significantly less that that of the control group (p = 0.05). In 31 of the 43 patients receiving treatment the initial 600 ml infusion was completed and the second amniotic fluid volume estimate was performed according to the protocol. However, 10 patients were delivered of their infants before the loading volume had been infused. In the remaining two patients the postinfusion ultrasonographic examination was not accomplished. In these 31 patients the mean amniotic fluid volume increased from 9.8 ± 3.8 to 14.7 ± 3.7 cm after infusion of the loading 600 ml of saline solution (p < 0.001). Maternal and neonatal outcome data are listed in Table III. For all but one of the outcome parameters studied, there was no significant difference between the treatment and control groups although a trend toward a decreased incidence of cesarean delivery because of fetal distress was noted in the amnioinfusion patients (4.7% vs 16%, P = 0.07, one-tailed). As has been previously reported,' we sought to determine the effects of parity on the incidence of cesarean delivery because of fetal distress between the amnioinfusion and control groups. However, unlike Miyazaki and Nevarez,' who found that amnioinfusion was more beneficial in primiparous women, we found in multiparous patients that the incidence of cesarean delivery because of fetal distress was 0% (0 of 22) in the amnioinfusion group versus 22% (8 of 36) in the control group (p = 0.02). A similar benefit was not seen in the primiparous patients (p = 1.0). An unexpected finding was a decreased incidence of postpartum endometritis in the amnioinfusion patients (2.4% vs 19%, P = 0.01). This difference could not be explained on the basis of a difference in the incidence of positive maternal group B streptococcal cultures of the cervix. Comment
The theoretical basis for amnioinfusion is that it reduces umbilical cord compression and variable fetal heart rate decelerations, a common cause of fetal dis-
1148 Owen, Henson, and Hauth
May 1990 Am J Obstet Gynecol
Table I. Study group assignments for amnioinfusion and control Category
P=
A mnioinfusion
Control
Total
Postterm pregnancy Variable decelerations in labor Pre term labor Oligohydramnios-growth retardation
5 13 II 14
6 20 18 13
11 33 29 27
TOTAL
43
57
100
0.71.
Table II. Demographic variables of amnioinfusion and control groups Treatment
Initial 4-quadrant AFV* (cm) Cervical examination randomization (cm) Gestational age (wk) Postterl!l (n = 11) Decelerations (n = 33) Preterm labor (n = 28) Oligo/IUGR (n = 26) Meconium-stained fluid Primiparous Birth weight (gm) Nonwhite Maternal age (yr) Epidural anesthesia Labor abnormality Oxytocin used Nuchal cord
Control
(N = 43)
(N = 57)
p
9.2 ± 3.7 3.7 ± 1.4
8.4 ± 3.1 3.6 ± 1.9
0.22 0.63
43 ± 0.33 40 ± 0.65 34 ± 1.8 40 ± 1.7 II (26%) 21 (49%) 2894 ± 657 29 (67%) 23 ± 5.0 29 (67%) 17 (40%) 32 (74%) 13 (30%)
43 ± 0.46 39 ± 2.6 34 ± 1.7 41 ± 1.6 19 (33%) 21 (37%) 2951 ± 755 39 (71 %) 23 ± 5.4 38 (67%) 28 (49%) 36 (63%) 18 (32%)
0.60 0.43 0.99 0.05 0.40 0.23 0.69 0.92 0.70 0.94 0.34 0.23 0.89
Test
AFV, Amniotic fluid volume; Oligo, oligohydramnios; [VCR, intrauterine growth retardation.
*Initial ultrasonographic examination not performed in four cases.
tress. 5 Since an unknown quantity of instilled fluid may leak out during the therapy, to date it has not been known how much is actually retained. Our results using a four-quadrant estimate show that amnioinfusion makes a significant impact on the amniotic fluid volume. Miyazaki and Nevarez' reported that variable decelerations in labor were ameliorated in 51 % of patients who received amnioinfusion versus only 4.2% of the control group and further noted that the effects of amnioinfusion were more pronounced in the primiparous group than in multiparous patients. Their series contained 48 nulliparous patients, and in this population the incidence of cesarean delivery because of fetal distress was 15% in the amnioinfusion group versus 48% in the control group (p = 0.03). Nageotte et al. l also reported that amnioinfusion had a significant impact on the incidence of variable decelerations in labor in patients with preterm premature rupture of the membranes; they also noted, as we have, a trend toward a decreased incidence of cesarean delivery because of fetal distress in the amnioinfusion group as compared with the control group (0.05 < P < 0.10). With optimal labor management, one would not ex-
pect a technique such as amnioinfusion to improve the immediate neonatal outcome, although Nageotte et al. l reported a significantly lower umbilical cord arterial pH in 32 control subjects compared with 29 amnioinfusion patients. However, as our results indicate, the incidence of cesarean delivery because of fetal distress was reduced in the treatment group, although the reduction did not reach statistical significance except in the multiparous patients. This is likely a result of our sample size since it would require 200 patients in each group to be 80% certain of detecting a 50% reduction in the rate of cesarean section because of fetal distress (from 16%, as in our control group, to 8%, one-tailed, a = 0.05). If a 25% reduction is considered clinically significant, then 910 patients in each group would be required. Nevertheless, the power of this study to detect a threefold difference in the incidence of cesarean delivery because of fetal distress (16% vs 4.7%), if this difference actually exists, is 0.99. Furthermore, we could demonstrate no harmful effects from either the placement of a second intrauterine pressure catheter or the saline solution amnioinfusion. In fact the maternal infection rate was significantly lower in the treatment group. This might be secondary
Saline amnioinfusion in labor
Volume 162 Number 5
1149
Table III. Maternal and neonatal outcome variables for amnioinfusion and control groups Treatment = 43)
(N
Operative delivery because of fetal distress Cesarean delivery Indicated operative vaginal delivery Total Total cesarean deliveries Postpartum endometritis Cord arterial pH
