Best Practice Guideline articleWhat (not) to do before delivery? Prevention of fetal meconium release and its consequences
Introduction
The appearance of meconium in the amniotic fluid before or during labour is often a source of anxiety for health workers. It has the potential to cause both direct harm to the newborn child, and indirect benefit or harm to mother or child by eliciting appropriate or inappropriate obstetric interventions.
Meconium staining of the amniotic fluid is a common occurrence, and increases with increasing gestational age, from 7% to 22% of term deliveries overall [1], [2], to 23% to 52% after 42 weeks [3], [4], [5], [6]. It is more common in babies of black African descent, [7] and is associated with reduced amniotic fluid index (< 5 cm) [8], with reduced middle cerebral artery pulsatility index [9], with maternal fever, [10] with opiate and cocaine use, [11] and with multiple nuchal cord loops in postdate pregnancies [12]. It may be associated with fetal compromise, but is also common in uncompromised labours. Thick but not thin meconium staining of the amniotic fluid is associated with poor perinatal outcome [13], [14].
The most important consequence of meconium staining of the amniotic fluid is meconium aspiration syndrome which occurs in 1% to 3% of pregnancies [15], [16], [17]. Meconium aspiration may occur before birth, or during the birth process, and is associated with significant morbidity. Meconium aspiration syndrome is an important cause of neonatal mortality in otherwise healthy term or post-term infants, with a case fatality rate of 5%-40% [16], [18], [19], [20].
Airways suctioning of the neonate may reduce, but does not eliminate the occurrence of meconium aspiration (see Vain NE, chapter 4). Strategies have therefore been sought to reduce fetal meconium aspiration before birth.
This review will attempt to provide a balanced view of the significance of meconium staining of the amniotic fluid, and evidence regarding strategies which may reduce either its occurrence or its impact on the pregnancy outcome. Particular attention will be paid to the following strategies:
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curtailing the duration of pregnancy
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avoiding harmful medication
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appropriate use of amniotomy
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clinical response to observed meconium staining of the amniotic fluid
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amnioinfusion.
Section snippets
Methods of the review
In order to identify pregnancy interventions before birth which might reduce or increase the risk of meconium passage or meconium aspiration syndrome, the Cochrane Library was searched on the term ‘meconium’. Those interventions identified which related to care before delivery were searched for any useful evidence on the outcomes ‘meconium-stained amniotic fluid’ and ‘meconium aspiration syndrome’. Where evidence from Cochrane reviews was not available, other review data were used. These data
Curtailing the duration of pregnancy
The physiological propensity of the fetus to pass meconium, and thus the incidence of meconium-stained amniotic fluid, increases with increasing gestational age (see Ghidini A, chapter 1). Preventing prolonged pregnancy by labour induction might reduce the risk of meconium-stained amniotic fluid. On the other hand, the process of labour induction might increase the risk of meconium passage by causing fetal hypoxia or by other mechanisms such as a direct effect of the induction agent on the
Avoiding harmful medication
In 1987 we reported an association between meconium-stained amniotic fluid and the ingestion of traditional herbal uterine stimulants (‘isihlambezo’) or castor oil [41]. We showed that isihlambezo stimulated both rat uterine and ileal smooth muscle in vitro [42], and postulated that smooth uterine stimulants might cross from mother to the fetus and cause meconium passage by direct stimulation of the bowel. We subsequently showed that misoprostol, a prostaglandin E1 analogue, and dinoprostone
Appropriate use of amniotomy
Amniotomy might in theory increase the risk of meconium-stained amniotic fluid by causing increased uterine contractions, increased direct pressure on the baby's head, or increased umbilical cord compression due to reduced amniotic fluid volume. Amniotomy (plus oxytocin) used for labour induction versus expectant management was associated with reduced meconium-stained amniotic fluid, presumably by curtailing prolonged pregnancy (Table 1 — see above).
In a review of two randomized trials of
Clinical response to observed meconium staining of the amniotic fluid
Meconium may be passed in response to fetal distress. The presence of meconium-stained amniotic fluid is thus commonly taken as an indication of possible fetal distress [1], [44].
However, the predictive values of meconium-stained amniotic fluid for fetal distress are poor [45], [46], [47], [48]. As with any diagnostic test with low predictive values, the potential exists for medical interventions in response to meconium-stained amniotic fluid to do more harm than good. In the absence of direct
Amnioinfusion
Amnioinfusion has been described as a method of preventing or relieving umbilical cord compression during labour [35], or of diluting meconium in the amniotic fluid to try to reduce the risk of meconium aspiration [49]. The technique is well described by Weismiller [50]. Saline or Ringer's lactate is usually infused through a purpose-designed intrauterine pressure catheter using an infusion pump. Studies from low-income countries where such catheters are unaffordable have demonstrated that
Oral hydration
Oral hydration has been shown to increase amniotic fluid volume in the short term [54]. Whether this strategy would dilute meconium and improve labour outcomes has not been assessed.
Other interventions during labour
Home-like versus conventional institutional settings for birth, epidural vs parental opioid analgesia, and immersion in water vs no immersion during 1st stage of labour have not been found to have any effect on the occurrence of meconium-stained amniotic fluid (Table 1).
Key guidelines
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Curtailment of prolonged pregnancy reduces the risk of meconium-stained amniotic fluid and meconium aspiration syndrome.
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Labour induction with prostaglandins, particularly misoprostol, appears to be associated with the occurrence of meconium-stained amniotic fluid.
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Amniotomy during labour may increase the risk for meconium aspiration syndrome.
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No evidence as to whether expediting delivery because of meconium-stained amniotic fluid alone improves outcome.
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Amnioinfusion for suspected umbilical cord
Research directions
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Specific research to determine the relationship between prostaglandin administration and meconium-stained amniotic fluid.
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Research to confirm the effect of amniotomy during labour on meconium aspiration syndrome.
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Research to determine the appropriate clinical response to meconium staining of the amniotic fluid.
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Research to determine the effect of oral or parenteral hydration on thick meconium staining of the amniotic fluid.
References (54)
- et al.
Assessment of fetal risk in postdate pregnancies
Am J Obstet Gynecol
(1988) - et al.
The usefulness of ultrasound assessment of amniotic fluid in predicting adverse outcome in prolonged pregnancy: a prospective blinded observational study
BJOG
(2003) - et al.
Fever in term labour
J Obstet Gynaecol Can
(2005) - et al.
Fetal meconium aspiration syndrome occurring despite airway management considered appropriate
Am J Obstet Gynecol
(1985) - et al.
Prediction of the severity of meconium aspiration syndrome
Am J Obstet Gynecol
(1993) - et al.
Labor induction versus expectant management for postterm pregnancies: a systematic review with meta-analysis
Obstetr Gynecol
(2003) - et al.
Meconium passed in labor: how reassuring is clear amniotic fluid?
Obstet Gynecol
(2003) - et al.
Therapeutic amnioinfusion for intrapartum fetal distress using a pediatric feeding tube
Int J Gynaecol Obstet
(2005) - et al.
Prognostic value of change in amniotic fluid color during labor
Obstet Gynecol Surv
(2005) Meconium aspiration syndrome — more than intrapartum meconium
N Engl J Med
(2005)
The influence of gestational age on the ability of the fetus to pass meconium in utero
Acta Obstet Gynecol Scand
Perinatal characteristics of uncomplicated post-date pregnancies
Obstet Gynecol
Interrelationships among abnormal cardiotocograms in labor, meconium staining of the amniotic fluid, arterial cord blood pH and Apgar scores
Obstet Gynecol
The epidemiology of preterm labor — a global perspective
J Perinat Med
The use of fetal Doppler cerebroplacental blood flow and amniotic fluid volume measurement in the surveillance of postdated pregnancies
Acta Obstet Gynecol Scand
Nuchal cords in term and postterm deliveries—do we need to know?
Obstet Gynecol
Obstetric and perinatal outcomes of pregnancies with term labour and meconium-stained amniotic fluid
Arch Gynecol Obstet
Meconium-staining of the liquor in a low-risk population
Paediatric Perinat Epidem
Intrauterine meconium aspiration
Obstet Gynecol
Risk factors for meconium aspiration syndrome
Aust N Z J Obstet Gynaecol
Failure to prevent meconium aspiration syndrome
Obstet Gynecol
Meconium aspiration syndrome: a 6-year retrospective study
Br J Obstet Gynaecol
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Meconium aspiration syndrome: A role for fetal systemic inflammation
2016, American Journal of Obstetrics and GynecologyCitation Excerpt :It is not known why only some, or which, neonates exposed to MSAF will develop MAS.1,18,24,25 Attempts to prevent MAS have included oropharyngeal,26,27 nasopharyngeal,26 and tracheal28-30 suctioning and amnioinfusion in women who have MSAF,31,32 but none of these interventions have proven effective.33-36 Typically, MAS affects term newborns with low Apgar scores (<7 at 5 minutes).1
Management strategy in case of meconium stained amniotic fluid
2014, Early Human DevelopmentCitation Excerpt :There is evidence that labor induction with prostaglandins, especially misoprostol, increases the risk of MSAF because placental crossing results in fetal bowel stimulation producing meconium. Amniotomy may increase the risk of MAS [3]. In the past, amnioinfusion has been advocated to prevent neonatal complications in case of MSAF.
The suctioning in the delivery room debate
2011, Early Human DevelopmentCitation Excerpt :Neither the administration of opiates to the mother to prevent newborn gasping, nor the increase in the number of C-sections has been able to prevent MAS. A recent review article by Hofmeyr has found evidence that prolonged pregnancies, amniotomy during labour, and the use of uterine stimulants (mainly misoprostol) increase the incidence of MSAF and MAS [13]. As regards to amnioinfusion for dilution of meconium-stained amniotic fluid, a recent systematic review by Hofmeyr and Xu has concluded that only in settings with limited peripartum surveillance the procedure may decrease the number of C-sections, MAS, need for mechanical ventilation, hospitalization rates and perinatal mortality [14].
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2016, Clinical and Experimental Obstetrics and GynecologyContemporary medical understanding of the'no-fault accident' during birth: Amniotic fluid embolism, pulmonary embolism, meconium aspiration syndrome, and cerebral palsy
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