Systematic review of the risk of uterine rupture with the use of amnioinfusion after previous cesarean delivery.

Objectives: Amnioinfusion is commonly used for the intrapartum treatment of women with pregnancy complicated by thick meconium or oligohydramnios with deep variable fetal heart rate decelerations. Its benefit in women with previous cesarean deliveries is less known. Theoretically, rapid increases in intrauterine volume would lead to a higher risk of uterine rupture.

Methods: Searches of the Cochrane Library from inception to the third quarter of 2001 and MEDLINE, 1966 to November 2001, were performed by using keywords "cesarean" and "amnioinfusion." Search terms were expanded to maximize results. All languages were included. Review articles, editorials, and data previously published in other sites were not analyzed.

Results: Four studies were retrieved having unduplicated data describing amnioinfusion in women who were attempting a trial of labor after previous cesarean section. As the studies were of disparate types, meta-analysis was not possible.

Conclusions: The use of amnioinfusion in women with previous cesarean delivery who are undergoing a trial of labor may be a safe procedure, but confirmatory large, controlled prospective studies are needed before definitive recommendations can be made.

Key Words: amnioinfusion, cesarean section, dehiscence, uterine rupture

**********

Amnioinfusion is a proven therapy for intrapartum management of thick meconium. It has been shown to decrease the rate of subsequent cesarean section, the finding of meconium below the vocal cords, and the incidence of meconium aspiration syndrome. (1-10) Its use in oligohydramnios is more debated. In women with oligohydramnios and fetal heart rate decelerations, it is of clear benefit in decreasing ominous fetal heart tracings and the need for cesarean delivery. (10-12) Data regarding its use prophylactically in women without such decelerations are not as clear. Although several studies attest to a decreased risk of cesarean section, fetal acidemia, or low Apgar score, (7-9,13-18) others have not shown benefit, (19-22) including a recent Cochrane Review. (23)

The use of amnioinfusion in women who have undergone previous cesarean section is less well studied. The principal concern is that rapid expansion of the intrauterine volume would lead to an increased risk of uterine rupture. This article will address that concern and evaluate the literature to date on the use of amnioinfusion in women with previous cesarean section.

Materials and Methods

Searches were performed by using MEDLINE and the Cochrane Library, including the Database of Systematic Review, the Controlled Trial Registry, and the Abstracts and Reviews of Effectiveness. The search of the Cochrane Library extended from its inception to the third quarter of 2001. MEDLINE was searched from 1966 to November 2001 by using the key words "amnioinfusion" and "cesarean." Total search yielded 63 articles. They were further selected by abstract to those articles that dealt in total or in part with women undergoing transcervical amnioinfusion who had at least one previous cesarean section. Only those studies that provided original data were included. Review articles were not analyzed. References from these studies were also evaluated for pertinence. To maximize yield of the search, separate searches were performed by using the words "cesarean," "cesarean section," "uterine rupture," and "uterine dehiscence" combined individually with "amnioinfusion." These searches yielded one article in addition to the three previously identified as satisfying the study criteria.

Results

Of the four articles, two were case reports (24,25) (one an uncontrolled case series (26) and one a retrospective cohort study). (27) Given the variability in study type, true meta-analysis is not possible. A description of the studies is as follows.

Adair et al (24) describe a woman admitted at term for induction for oligohydramnios. After artificial rupture of membranes, the fetal heart rate tracing showed moderate variable decelerations, although the degree of fetal heart rate deceleration was not discretely defined. Amnioinfusion of 600 mL normal saline was accomplished with the aid of an electronic infusion pump. The fetal heart tracing initially improved, but there was subsequent severe fetal bradycardia accompanied by abdominal pain. On emergency cesarean section, uterine rupture was identified.

Gimovsky et al (25) also describe a woman with a term gestation admitted for induction secondary to oligohydramnios. The patient was induced with Prostin gel and subsequently with oxytocin. At artificial rupture of membranes, a small amount of thick meconium was noted. Fetal heart tracing was reactive. An amnioinfusion of 500 mL normal saline bolus was followed by 125 mL per hour. Three hours later, repetitive deep variable decelerations were noted. Repeat cesarean section was performed and revealed complete dehiscence of the previous uterine incision. In both cases, the outcomes for the baby and the mother were good.

The case series of Strong et al (26) describes 18 women who received amnioinfusion for the indications of oligohydramnios and/or deep variable decelerations during their trial of labor. Three patients had repeat cesarean section secondary to arrest of labor. The remaining 15 women delivered vaginally, giving a rate for successful trial of labor after cesarean section (TOLAC) of 83%. The rate of successful TOLAC in their institution was 70.9% overall. There were no cases of uterine rupture or dehiscence. All scars were examined at delivery by palpation of the uterine scar by vaginal examination. Amnioinfusion was accomplished by means of the gravity flow method in 78% of cases and by infusion pump in 22%. Total volumes infused were not listed. Boluses ranged from 250 to 500 mL. The rate of complications of amnioinfusion beyond uterine rupture was not discussed.

Ouzounian et al (27) presented the largest sample size of studies retrieved. This retrospective cohort study has two control groups: women undergoing a TOLAC who did not undergo amnioinfusion and those who had not had a previous cesarean who required amnioinfusion. Of the 1,436 women in the TOLAC group, 122 (8.5%) underwent amnioinfusion and represent the study cohort. The indication for amnioinfusion was oligohydramnios in 79%, meconium in 11%, and variable decelerations in 8%. Amnioinfusion was performed by means of the gravity method, with bolus amounts of 250 mL in those patients with an amniotic fluid index of 5 and 10 cm and 500 mL normal saline if less than 5 cm. The amounts infused for the other indications were not described.

Table 1 describes the rate of complications in women who underwent amnioinfusion. Of note, there was no increased risk of uterine rupture. The power to detect a small difference, however, was not great. Therefore, the uterine rupture rate of 0.8% among women undergoing a TOLAC and amnioinfusion, albeit fully within the national averages for women undergoing a TOLAC, and less than the 1.1% rate of uterine rupture at their institution, cannot be definitively established to be of similar or decreased risk. Regarding other complications, the rate of amnionitis was significantly increased for those women who had had a previous cesarean section, with a relative risk of 1.75 (1.19 to 2.58) (Table 2).

Discussion

There is insufficient evidence to draw firm conclusions concerning the safety of amnioinfusion in women with a previous cesarean delivery. The data, as they exist, have several limitations. Most importantly, there are simply very few studies that have been done pertaining to its use in women undergoing TOLAC. Those that do exist are of varying study types and scientific quality. Case reports, although interesting and often highlighting important points, are of limited scientific validity. Uncontrolled descriptive studies similarly serve more to define the problem than to come to its answer. Only controlled cohort studies and prospective, randomized, controlled trials may serve to bring this question to its resolution.

Also complicating the current data is the use of adjunctive therapies in women without spontaneous labor or those who require augmentation. Both the use of prostaglandin for cervical ripening and oxytocin for induction or augmentation of labor have been shown to increase the risk of uterine rupture. (28) Control for these factors was not made in the above studies secondary to their small sample size and study type.

Of further note is the rate of complications beyond uterine rupture. Contrary to the finding of similar or decreased risk of infection in other studies, (11,29,30) Ouzounian et al found a 9.1% absolute increase in the risk for amnionitis. This led to a surprising number needed to harm of 11. That is to say, in women undergoing amnioinfusion during a TOLAC compared with those without previous cesarean, 1 more out of every 11 may have amnionitis, presumably requiring antibiotics and prolonging hospital stay. Whether this potential increased risk would be replicated in larger studies remains to be established.

Of particular concern, though, is the indication justifying the use of amnioinfusion. If one considers deep variable decelerations a predictor of uterine rupture, using amnioinfusion in the face of decelerations in patients with oligohydramnios may lead to women not being treated for cord compression but instead further compromising a uterus predisposed to rupture. Its use in pregnancies complicated by thick meconium remains potentially more appropriate.

Conclusion

It is clear that further studies are needed to determine if amnioinfusion in women undergoing a trial of labor after cesarean section is a safe procedure and does not increase the risk of uterine rupture. It is unlikely, though, that there will be sufficient data available in the near future to answer this question. Assuming a baseline rate of uterine rupture of 7 to 8 per 1,000 women undergoing a TOLAC, to detect a 20% difference with 80% statistical power (d = 0.80) would require that more than 27,000 women be enrolled in the amnioinfusion arm. This is 225 times the size of the largest study to date. A study of such enormity is difficult to imagine.

Less extensive works will have to suffice. It is recommended in this study that they be prospective, randomized, controlled trials or large controlled, retrospective, cohort studies, as seen in the work of Ouzounian and colleagues. (27) Also, future studies will need to evaluate what components of the care provided by Ouzounian and colleagues led to the unchanged risk of uterine rupture they observed. These included (1) using small volumes of 250 to 500 mL normal saline for a bolus, (2) confirming good backflow before infusing a maintenance rate, and (3) infusing it through the gravity flow technique and not on an infusion pump. (Glantz and Letteney (31) similarly found an increased risk of fetal distress when infusion pumps were used.) Pending repetition of their work, the state of the literature is insufficient to recommend unequivocally for or against the use of amnioinfusion in women after previous cesarean delivery.

Whatever is begun in anger ends in shame.
--Benjamin Franklin

Table 1. Maternal and neonatal complications among patients who received
amnioinfusion

                        Previous          No previous
                        cesarean section  cesarean section

Maternal complications
  Amnionitis             26 (21.3%)        99 (12.2%)
  Uterine dehiscence      0                 0
  Uterine rupture         1 (0.8%)          0
Neonatal complications
  Meconium below cords    3 (2.4%)         14 (1.8%)
  Meconium aspiration     0                 7 (0.9%)
  5-min Apgar <7          3 (2.4%)          7 (0.9%)

                        Relative risk (95%
                        confidence interval)  Significance

Maternal complications
  Amnionitis             1.75 (1.19-2.58)      P < 0.01
  Uterine dehiscence     ...                   ...
  Uterine rupture        ...                   ...
Neonatal complications
  Meconium below cords   1.43 (0.42-4.88)      P = 0.84
  Meconium aspiration    ...                   P = 0.64
  5-min Apgar <7         2.86 (0.75-10.91)     P = 0.26

Statistically significant ([chi square]), < 0.05.
Ouzounian JG, Miller DA, Paul RH. Amnioinfusion in women with previous
cesarean births: a preliminary report. Am J Obstet Gynecol 1996; 174:
783-786 (reprinted with permission).

Table 2. Incidence of uterine rupture among patients with previous
cesarean births who underwent trial of labor

                                    No
                     Amnioinfusion  amnioinfusion

No. of patients      122             1314
Successful VBAC (%)   71 (58.2)     1,006 (76.5)
Uterine rupture (%)    1 (0.8)         15 (1.1)

                     Relative risk (95%
                     confidence interval)  Significance

No. of patients      ...                   ...
Successful VBAC (%)  0.76 (0.65-0.89)      P < 0.01 (a)
Uterine rupture (%)  0.72 (0.10-5.39)      P = 0.60 (b)

VBAC, vaginal birth after cesarean.
(a) [chi square] test.
(b) Fisher exact test.
Ouzounian JG, Miller DA, Paul RH. Amnioinfusion in women with previous
cesarean births: a preliminary report. Am J Obstet Gynecol 1996; 174:
783-786. (reprinted with permission).

Accepted February 4, 2004.

References

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RELATED ARTICLE: Key Points

* Amnioinfusion is commonly used in modern obstetric practice.

* Many physicians hesitate to use it in women with a previous uterine scar.

* Review of the literature is inconclusive as to whether there is an increased risk of uterine rupture among women undergoing amnioinfusion who have had previous cesarean section.

Paul Hicks, MD

From Salud Family Health Center, Fort Lupton, CO.

Reprint requests to Paul Hicks, MD, 1115 Second Street, Fort Lupton, CO 80621. Email: [e-mail]