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 meconium /me·co·ni·um/ (mi-ko´ne-um) dark green mucilaginous material in the intestine of the full-term fetus.
1. or oligohydramnios with deep variable fetal heart rate fetal heart rate Obstetrics A rate which, in the non-stressed fetus, reflects cardioaccelerator and cardiodecelerator reflexes; analysis of the FHR requires evaluation of a baseline FHR between uterine contractions or periodic changes in the FHR and non-periodic, decelerations. Its benefit in women with previous cesarean cesarean /ce·sar·e·an/ (se-zar´e-an) see under section.
ce·sar·e·an or cae·sar·e·an or cae·sar·i·an or ce·sar·i·an
Of or relating to a cesarean section. deliveries is less known. Theoretically, rapid increases in intrauterine intrauterine /in·tra·uter·ine/ (-u´ter-in) within the uterus.
Within the uterus.
Situated or occuring in the uterus. 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 The online medical database of the U.S. National Library of Medicine (NLM) whose parent is the National Institutes of Health, Bethesda, MD. MEDLINE contains millions of articles from thousands of medical journals and publications. The consumer section of the site (http://medlineplus. , 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 cesarean section (sĭzâr`ēən), delivery of an infant by surgical removal from the uterus through an abdominal incision. The operation is of ancient origin: indeed, the name derives from the legend that Julius Caesar was born in this . 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 dehiscence /de·his·cence/ (de-his´ins) a splitting open.
wound dehiscence separation of the layers of a surgical wound.
n. , 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 vocal cords: see larynx.
The pair of elastic, fibered bands inside the human larynx. The cords are covered with a mucous membrane and pass horizontally backward from the thyroid cartilage (Adam's apple) to insert on , and the incidence of meconium aspiration syndrome Meconium aspiration syndrome
Breathing in of meconium (a newborn's first stool) by a fetus or newborn, which can block air passages and interfere with lung expansion. . (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 acidemia /ac·i·de·mia/ (as?i-de´me-ah) increased acidity of the blood. For those characterized by increased concentration of a specific acid, see at the acid. , or low Apgar score Ap·gar score
A system of evaluating a newborn's physical condition by assigning a value (0, 1, or 2) to each of five criteria: heart rate, respiratory effort, muscle tone, response to stimuli, and skin color. , (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 controlled trial Clinical research A clinical study in which one group of participants receives an experimental drug while the other receives either a placebo or an approved–'gold standard' therapy. See Blinding, Double-blinded. 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 uterine /uter·ine/ (u´ter-in) pertaining to the uterus.
Of, relating to, or in the region of the uterus. dehiscence" combined individually with "amnioinfusion." These searches yielded one article in addition to the three previously identified as satisfying the study criteria.
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 Rupture of membranes (ROM) is a term used during pregnancy to describe a rupture of the amniotic sac at the onset of, or during, labor. This is colloquially known as "breaking water". , the fetal heart rate tracing showed moderate variable decelerations, although the degree of fetal heart rate deceleration deceleration /de·cel·er·a·tion/ (de-sel?er-a´shun) decrease in rate or speed.
early deceleration was not discretely defined. Amnioinfusion of 600 mL normal saline normal saline Physiologic saline solution, see there was accomplished with the aid of an electronic infusion pump infusion pump A device designed to deliver drugs and/or 'biologicals', at low doses and at a constant or controllable rate; ↑ rates of delivery in such devices may be associated with local hemolysis, compromising the potential benefits of a calibrated delivery . The fetal heart tracing initially improved, but there was subsequent severe fetal bradycardia bradycardia: see arrhythmia. 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 oxytocin (ŏksĭtō`sĭn), hormone released from the posterior lobe of the pituitary gland that facilitates uterine contractions and the milk-ejection reflex. . 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 bolus /bo·lus/ (bo´lus)
1. a rounded mass of food or pharmaceutical preparation ready to swallow, or such a mass passing through the gastrointestinal tract.
2. a concentrated mass of pharmaceutical preparation, e. 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 TOLAC Trial of Labor After Cesarean ) 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 palpation /pal·pa·tion/ (pal-pa´shun) the act of feeling with the hand; the application of the fingers with light pressure to the surface of the body for the purpose of determining the condition of the parts beneath in physical diagnosis. 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 amniotic fluid
The fluid within the amnion that surrounds the fetus and protects it from injury.
The liquid that surrounds the baby within the amniotic sac. 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).
There is insufficient evidence insufficient evidence n. a finding (decision) by a trial judge or an appeals court that the prosecution in a criminal case or a plaintiff in a lawsuit has not proved the case because the attorney did not present enough convincing 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 ran·dom·ize
tr.v. ran·dom·ized, ran·dom·iz·ing, ran·dom·iz·es
To make random in arrangement, especially in order to control the variables in an experiment. , 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 prostaglandin (prŏs'təglăn`dən), any of a group of about a dozen compounds synthesized from fatty acids in mammals as well as in lower animals. for cervical ripening cervical ripening Obstetrics The stromal response of the cervix in phase 1 of parturition, which precedes the onset of labor, in which the cervix becomes softer and more dilatable. See Cervical effacement. 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 The number needed to harm (NNH) is an epidemiological measure that indicates how many patients need to be exposed to a risk-factor to cause harm in one patient that would not otherwise have been harmed. It is defined as the inverse of the attributable risk. 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 pre·sum·a·ble
That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster. 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 pre·dis·pose
v. pre·dis·posed, pre·dis·pos·ing, pre·dis·pos·es
a. To make (someone) inclined to something in advance: to rupture. Its use in pregnancies complicated by thick meconium remains potentially more appropriate.
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 backflow /back·flow/ (-flo) reflux or regurgitation (1).
pyelovenous backflow drainage from the renal pelvis into the venous system occurring under certain conditions of back pressure. 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.
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Aspiration of amniotic fluid contaminated with meconium by a fetus in hypoxic distress. in labor using amnioinfusion. Obstet Gynecol 1989;73:647-651.
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9. De Meeus JB, Magnin G, Vequeau V, et al. Prophylactic amnion Amnion
A thin, cellular, extraembryonic membrane forming a closed sac surrounding the embryo in all reptiles, birds, and mammals. It is present only in these forms; the collective term amniotes is applied to these animals. infusion during labor: apropos of 195 cases. J Gynecol Obstet Biol Reprod 1997;26:610-616.
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Induction of labor involves using artificial means to assist the mother in delivering her baby.
Purpose and newborn outcome. Ginekol Pol 2000;71:837-842.
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18. Mino M, Puertas A, Herruzo AJ, et al. Amnioinfusion in labor induction of term pregnancies with premature rupture of membranes Premature Rupture of Membranes Definition
Premature rupture of membranes (PROM) is an event that occurs during pregnancy when the sac containing the developing baby (fetus) and the amniotic fluid bursts or develops a hole prior to the start of labor. and low amniotic fluid. In J Gynaecol Obstet 1998;61:135-140.
19. Nageotte MPO MPO myeloperoxidase.
MPO Myeloperoxidase, see there , Bertucci L, Towers CV, et al. Prophylactic amnioinfusion in pregnancies complicated by oligohydramnios; a prospective study. Obstet Gynecol 1991;77:677-680.
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24. Adair CD, Sanchez-Ramos L, Kaunitz AM, et al. A trial of labor complicated by uterine rupture following amnioinfusion. South Med J 1995;88:847-848.
25. Gimovsky ML, Bayer-Zwirello LA, Plevyak M. Fetal heart rate monitoring casebook A printed compilation of judicial decisions illustrating the application of particular principles of a specific field of law, such as torts, that is used in Legal Education to teach students under the Case Method system. . J Perinatol 1997;17:83-86.
26. Strong TH Jr, Vega JS, O'Shaughnessy MJ, et al. Amnioinfusion among women attempting vaginal birth after cesarean vaginal birth after cesarean VBAC Obstetrics Vagina delivery of an infant after a cesarean section Complications Uterine apoplexy delivery. Obstet Gynecol 1992;79:673-674.
27. Ouzounian JG, Miller DA, Paul RH. Amnioinfusion in women with previous cesarean births: a preliminary report. Am J Obstet Gynecol 1996;174:783-786.
28. Lydon-Rochelle M, Holt VL, Easterling TR, et al. Risk of uterine rupture during labor among women with a prior cesarean delivery. N Engl J Med 2001;345:3-8.
29. Owen J, Henson BV, Hauth JC. A prospective randomized study of saline solution saline solution
A solution of any salt, usually an isotonic sodium chloride solution. Also called salt solution.
A solution of sterile water and salt used in a variety of medical procedures. amnioinfusion. Am J Obstet Gynecol 1990;162:1146-1149.
30. Moen MD, Besinger RE, Tomich PG, et al. Effect of amnioinfusion on the incidence of postpartum endometritis endometritis /en·do·me·tri·tis/ (-me-tri´tis) inflammation of the endometrium.
puerperal endometritis that following childbirth. in patients undergoing cesarean delivery. J Reprod Med 1995;40:383-386.
31. Glantz JC, Letteney DL. Pumps and warmers during amnioinfusion: is either necessary? Obstet Gynecol 1996;87:150-155.
RELATED ARTICLE: Key Points
* Amnioinfusion is commonly used in modern obstetric ob·stet·ric or ob·stet·ri·cal
Of or relating to the profession of obstetrics or the care of women during and after pregnancy.
pertaining to or emanating from obstetrics. 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: firstname.lastname@example.org