Version May 2024
INTRODUCTION — Amnioinfusion refers to the instillation of fluid into the amniotic cavity. The rationale is that augmenting amniotic fluid volume may decrease or eliminate problems associated with a severe reduction or absence of amniotic fluid, such as severe variable decelerations during labor. The procedure can be performed by transcervical or transabdominal routes. Transcervical amnioinfusion for the treatment of recurrent variable decelerations is the most common indication. Other possible uses include transabdominal amnioinfusion to aid in ultrasound diagnosis or to aid external cephalic version, although supporting data are lacking.
This topic will discuss the indications, techniques, and monitoring of transcervical amnioinfusion for management of recurrent variable decelerations in labor. Information on topics related to amniotic fluid and amniocentesis are presented separately.
●(See "Physiology of amniotic fluid volume regulation".)
●(See "Assessment of amniotic fluid volume".)
●(See "Diagnostic amniocentesis".)
In this topic, when discussing study results, we will use the terms "woman/en" or "patient(s)" as they are used in the studies presented. We encourage the reader to consider the specific counseling and treatment needs of transgender and gender-expansive individuals.
INDICATIONS — In general, amnioinfusion is a second-line intervention for persistent variable decelerations seen on fetal heart rate tracings during labor and appears to decrease the risk of meconium aspiration syndrome in the setting of moderate to thick amniotic-stained fluid [1,2].
●(See "Meconium aspiration syndrome: Management and outcome".)
Amnioinfusion does not appear to be helpful for treatment of chorioamnionitis or oligohydramnios, or thick meconium [3,4]. Its role in oligohydramnios resulting from bilateral renal agenesis is a focus of study [5].
●(See "External cephalic version", section on 'Other'.)
●(See "Preterm prelabor rupture of membranes: Management and outcome", section on 'Amnioinfusion'.)
●(See "Prelabor rupture of membranes before and at the limit of viability", section on 'Amnioinfusion'.)
●(See "Clinical chorioamnionitis".)
PREPARATION
●Informed consent – As with all procedures, patients undergoing amnioinfusion are consented for treatment. The main benefit is avoiding cesarean delivery in individuals with recurrent variable decelerations during labor. The main risk is that the procedure does not resolve the concerning fetal heart tracing pattern and the patient requires a cesarean delivery. Additional risks, albeit extremely rare, include umbilical cord prolapse, amniotic fluid embolism, placental abruption, chorioamnionitis, and uterine rupture [6-8]. (See 'Complications' below.)
●Prophylactic antibiotics – In the absence of other indications for antibiotic use, we do not administer antibiotics during amnioinfusion. A randomized trial showed that prophylactic use of cefazolin in the infusate (1 g/1000 mL of normal saline) did not significantly reduce rates of maternal or neonatal infection [9].
MATERIALS AND EQUIPMENT — The materials and equipment are all items that are typically available on any labor and delivery unit. Required materials include:
●Catheter (intrauterine pressure catheter [preferred] or pediatric nasogastric feeding tube).
●Solution for infusion (Lactated Ringer solution without dextrose [preferred] or normal saline).
●Method of infusion.
●Tubing to connect the components. We advise using an infusion pump because it allows instillation of a known rate of fluid, but gravity drainage is possible. (See 'Transcervical approach' below.)
We prefer Lactated Ringer to normal (0.9 percent) saline because the latter may cause small changes in the concentration of fetal electrolytes [10]. However, the electrolyte concentrations remain in the physiologic range so normal saline is an acceptable alternative if Lactated Ringer solution is not available [11,12]. There is no evidence that the fluid needs to be warmed above ambient room temperature prior to administration; however, warming the fluid to body temperature is a common practice [13,14]. A blood warmer should be used rather than a blanket or surgical fluid warming oven since ovens warm fluid to a wide range of temperatures [15].
TRANSCERVICAL APPROACH — The transcervical approach is the route used for laboring patients because the fetal membranes must be ruptured for transcervical infusion. (See 'Indications' above.)
Catheter insertion — An intrauterine pressure catheter (IUPC) is inserted using standard technique described in the package materials and attached to intravenous extension tubing. While a pediatric nasogastric feeding tube can be used if an IUPC is not available, we prefer to avoid feeding tubes because intrauterine pressure monitoring cannot be performed through a feeding tube [16]. (See "Use of intrauterine pressure catheters", section on 'Technique'.)
Infusion protocol — Sterile fluid is infused through the catheter into the amniotic cavity. We use the following protocol:
•Bolus amount: 250 mL to 600 mL of Lactated Ringer solution without dextrose given over 30 to 60 minutes
•Continuous infusion rate: 200 mL/hr of Lactated Ringer solution without dextrose
-The continuous infusion rate is begun at the completion of the bolus above.
-Continuing the infusion may help to prevent recurrence of decelerations as some fluid will usually leak from the uterine cavity during and after the infusion.
•End point: The infusion is continued until delivery is achieved, a safety concern is encountered, or it is determined that the amnioinfusion is not having the desired effect (ie, the variable decelerations do not resolve). (See 'Safety monitoring' below.)
It is important to note that infusion protocols vary across institutions and no one protocol has been proven superior. A survey of United States obstetric units revealed that they used the following methods in decreasing order of frequency: (1) a fluid bolus (50 to 1000 mL) followed by a constant infusion, (2) serial boluses (200 to 1000 mL administered every 20 minutes to four hours), and (3) constant infusion (15 to 2250 mL/hour) [6]. A randomized trial found that continuous and intermittent infusions were similarly effective [17]. Although most units use an infusion pump, this method has not been shown to result in better outcomes than gravity alone [13].
Because it is possible to introduce fluid into the uterus too rapidly, the American College of Obstetricians and Gynecologists recommends that each obstetric unit establish a protocol for intrauterine pressure monitoring during amnioinfusion or limiting the volume and rate of infusion when the technique is used [18].
Safety monitoring — We continually assess the following parameters during amnioinfusion:
●Fetal heart rate should be monitored continuously to determine whether the variable decelerations resolve and to identify the occurrence of new nonreassuring fetal heart rate patterns. We stop the infusion if the intervention is not achieving a clinically desirable effect.
●Assess uterine resting tone every 30 minutes to prevent excessive infusion of fluid. If the resting tone (between contractions) is noted to increase by more than 15 mmHg above the baseline, we slow or stop the infusion.
●Assess fluid per vagina (color and amount) every 30 minutes. We stop the infusion if fluid becomes frankly bloody or no fluid is noted to leak out.
●Assess maternal respiratory status. We stop the infusion if concerns for fluid overload arise.
If the amnioinfusion achieves the desired resolution of decelerations but the decelerations recur after the amnioinfusion is discontinued, reinitiation can be performed with the above safety monitoring.
If the amnioinfusion fails to achieve the desired resolution of decelerations in the desired amount of time, then we take other indicated measures to address the nonreassuring tracing. (See "Intrapartum category I, II, and III fetal heart rate tracings: Management".)
TRANSABDOMINAL APPROACH — Transabdominal amnioinfusion has been described for the evaluation and diagnosis of fetal anomalies in the setting of second-trimester oligohydramnios, to prolong pregnancy following midtrimester preterm premature rupture of membranes (PPROM), and to facilitate external cephalic version.
●Second-trimester oligohydramnios – Although uncommon in general practice, when used, the transabdominal approach is primarily restricted to pregnancies with midtrimester oligohydramnios or anhydramnios, where it is performed to enhance ultrasound imaging or to facilitate bladder or renal pelvis shunt placement in cases of obstructive uropathies. In a retrospective descriptive study of 61 pregnancies diagnosed with severe oligohydramnios between 17 and 26 weeks of gestation, use of amnioinfusion increased the mean number of diagnosed ultrasound findings from 0.39 (±0.45) to 1.59 (±1.24) [19]. The most frequently diagnosed abnormalities were renal (59 percent), previously undiagnosed PPROM (21 percent), and fetal growth restriction (18 percent).
Of note, although there are case reports, case series, and retrospective reviews of using serial amnioinfusion in pregnancies complicated by oligohydramnios, repeated amnioinfusion is not an established management strategy for these individuals [20-23]. Serial amnioinfusion in the setting of midtrimester PPROM is controversial. An ongoing multicenter randomly-assigned trial is comparing the use of serial amnioinfusion with expectant management following midtrimester PPROM [24]. (See "Prelabor rupture of membranes before and at the limit of viability", section on 'Amnioinfusion'.)
The transabdominal procedure does not differ from amniocentesis, except fluid is instilled rather than removed. Room temperature Lactated Ringer solution is manually infused until the desired level of ultrasound visualization is achieved. The infused volume is generally less than 100 mL. (See "Diagnostic amniocentesis".)
●Third-trimester external cephalic version – While transabdominal amnioinfusion has been proposed to aid external cephalic version (ECV) of breech or transverse fetuses at term, supporting data are sparse, and thus we do not advise using amnioinfusion for this indication. A 2015 systematic review of trials and quasi-randomized trials reported that the body of evidence was insufficient to permit conclusions regarding efficacy and safety [25]. A subsequent trial reported no differences in the rates of cephalic presentation at delivery for 119 self-reported women at term with a breech fetus and one prior unsuccessful ECV attempt that were randomly assigned to amnioinfusion or no infusion prior to repeat ECV with a senior obstetrician (20 versus 12 percent) [26].
COMPLICATIONS — Complications of transcervical amnioinfusion are rare. While maternal amniotic fluid embolism has been described in case reports, a clear relationship to the procedure has not been documented [8,27]. Similarly, there does not appear to be any additional risk of cord prolapse [28] or uterine rupture in self-reported women with previous cesarean delivery [29]. Transcervical amnioinfusion may increase the risk of chorioamnionitis by washing out the amniotic fluid, which has bacteriostatic properties, or by the introduction of a foreign body to a region colonized by bacteria. In a meta-analysis that included one trial of 116 self-reported women, amnioinfusion was associated with increased risk of postpartum fever, but not with postpartum endometritis [30]. However, it is impossible to exclude the possibility of a small increase in risk given the small number of reported complications.
Iatrogenic complications have also been rarely reported. Iatrogenic polyhydramnios has been described and was associated with elevated intrauterine pressure and fetal bradycardia [31]. A case report attributed excessive fluid infusion and intrauterine manipulation to development of a shoulder presentation in a previously vertex presenting fetus [32]. In addition, there is potential risk for placental injury or disruption by the intrauterine pressure catheter, particularly at the time of placement.
Data regarding complications of transabdominal amnioinfusion are sparse because this technique is not routine and because it is typically employed in pregnancies that have additional complications, such as oligohydramnios or preterm premature rupture of the membranes (PPROM). One trial of 58 self-reported women reported no differences in maternal or fetal outcomes among those assigned to receive serial amnioinfusion for very early PPROM compared with expectant management.
SUMMARY AND RECOMMENDATIONS
●Procedure and indications – Amnioinfusion, or the instillation of fluid into the amniotic cavity, is a second-line intervention for persistent variable decelerations seen on fetal heart rate tracings during labor. As with all procedures, patients undergoing amnioinfusion are consented for treatment. Antibiotic prophylaxis is not indicated. (See 'Indications' above and 'Preparation' above.)
●Materials and equipment – The materials and equipment are those commonly found on labor and delivery units and include a catheter, solution, infusion pump, and connecting tubing. We prefer Lactated Ringer to normal (0.9 percent) saline because the latter may cause small changes in the concentration of fetal electrolytes. However, the electrolyte concentrations remain in the physiologic range so normal saline is an acceptable alternative if Lactated Ringer solution is not available. (See 'Materials and equipment' above.)
●Transcervical infusion during labor – The transcervical approach is the route used for laboring patients; the fetal membranes must be ruptured for transcervical infusion.
•Protocols – Protocols for amnioinfusion vary across institutions. There is no evidence that any one method is superior in terms of safety, efficacy, or complications rates. (See 'Transcervical approach' above.)
•Monitoring – During transcervical amnioinfusion, we routinely monitor the infusion rate, fetal heart rate, fluid per vagina, and maternal respiratory status. (See 'Safety monitoring' above.)
●Transabdominal infusion – Transabdominal amnioinfusion has been described for the evaluation and diagnosis of fetal anomalies in the setting of second trimester oligohydramnios and to facilitate external cephalic version. However these are not standard indications and supporting data are sparse. (See 'Transabdominal approach' above.)
●Risks and complications – The main risk of amnioinfusion is that it may not resolve a concerning fetal heart rate tracing. Rare complications have been reported including amniotic fluid embolism, cord prolapse, and uterine rupture, although it is not clear if the amnioinfusion was the cause. (See 'Complications' above.)
ACKNOWLEDGMENTS — The editorial staff at UpToDate acknowledge Henry Roque, MD, MS, Jonathan Gillen-Goldstein, MD, and Edmund Funai, MD, who contributed to an earlier version of this topic review.
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