13 Meconium. Handbook CTG

 13

Meconium

◈

Why Is It Harmful?

Nirmala Chandrasekaran and Leonie Penna

Handbook of CTG Interpretation: From Patterns to Physiology, ed. Edwin Chandraharan.

Published by Cambridge University Press. © Cambridge University Press 2017.

Key Facts

Physiological: As the fetal gut reaches maturity, peristaltic contractions of the

bowel occur spontaneously as part of normal development. Forty-four per cent of

fetuses beyond 42 weeks of gestation will have passed meconium. The majority of cases

of meconium-stained amniotic fluid (MSAF) at term are physiological. Physiological

meconium is always light as there should be a normal volume of amniotic fluid, and as it

is rare for meconium to be passed by the fetus before 37 weeks, gestation will usually

be beyond 37 weeks with even greater reassurance offered by postterm gestations.

There should be no risk factors for placental insufficiency, intrapartum hypoxia or

infection in order to consider meconium as physiological. The parasympathetic nervous

system increases overall gut motility, and thus meconium can be passed during labour as

a result of head compression via a vagally mediated response. This response is

uncommon during the first stage of labour and is most commonly seen in the passage of

meconium during the late second stage in healthy infants born with no evidence of

infection or acidosis.

Causes of meconiumFetal hypoxia: Reduction in the amount of oxygen available to a fetus in labour

results in an adrenergic response with a rising fetal heart rate (FHR) and redistribution

of blood to essential organs with a reduction in blood flow to nonessential organs

including the bowel. This and a direct vagal effect can result in peristaltic bowel

contractions and relaxation of the anal sphincter resulting in the passage of meconium.

This effect is most commonly seen in a gradually developing hypoxia and may not occur

in chronic long-standing hypoxia or in acute severe hypoxia (such as massive

abruption).

Maternal obstetric cholestasis: MSAF is more common in woman with a

diagnosis of obstetric cholestasis especially where bile acids are >40 micromoles per

litre with rates of 25 per cent reported in term and 18 per cent in preterm labour.

Fetal bowel abnormality: Gastroschisis increases the likelihood of MSAF during

labour (including preterm). The reason for this effect is not certain but is possibly due to

the direct contact of the bowel with the amniotic fluid stimulating peristaltic

contractions.

Listeriosis: Fetal listeria infection is reported to cause MSAF in preterm labour

but is very rare and unlikely to be the cause of MSAF. Maternal blood cultures should

be taken for listeria, but other infective pathologies or hypoxia are more common and

should be considered.

Fetal infection: Meconium increases the risk of chorioamnionitis as it inhibits

neutrophil phagocytosis and as a result enhances bacterial growth.

Recommended Management

CTG monitoring must always be considered in labours complicated by

meconium-stained liquor because of its association with hypoxia and infection.

However, the fact that most meconium is physiological has resulted in conflicts

regarding the level of intervention appropriate in the low-risk pregnancy.

The woman should be advised that in the majority of cases meconium represents

a physiological response in the maturing fetus but that in a small number of cases

it may be an indicator of a fetal problem and that it is important to detect anyTable 13.1 Suggested plan of management for CEFM in the presence of meconium

Quantification of meconium

Light Heavy

falling oxygen levels as this may result in fetuses gasping with the effect of

meconium entering their lungs causing meconium aspiration syndrome (MAS).

The importance of fetal monitoring in identifying a fetus that is becoming

stressed by labour should be explained with reassurance that this monitoring is

effective.

For thin meconium in gestations >37 weeks with no risk factors for placental

insufficiency or infection, continuous electronic fetal monitoring (CEFM) is not

deemed mandatory by some national guidelines. However, intermittent

auscultation (IA) and maternal observations for signs of sepsis must be

performed to the highest standard with immediate conversion to CEFM if any

new risk factor or pyrexia develops or there are concerns about the quality or

findings of IA (e.g. a progressive rise in baseline FHR).

In any type of meconium with any risk factor for infection or development of

intrauterine hypoxia, CEFM should be recommended and commenced for the

duration of labour. CEFM should also be recommended for thin MSAF in

women with previous clear liquor who develop meconium as a new finding or if

labour becomes prolonged.

If fetal heart monitoring is normal, then no specific action is required regardless

of the type of meconium or the presence of signs of infection. With thick

meconium and possible infection, a careful review of labour progress is prudent,

with delivery considered if the interval until spontaneous delivery is likely to

take many hours.

In order to ensure that management is optimized, it is important to consider the

underlying pathophysiology that may be indicated by the trace. Table 13.1

summarizes a suggested plan of management for CEFM in the presence of

meconium.Is there possible infection (fetal tachycardia, maternal tachycardia or

maternal pyrexia?

No Yes No Yes

CTG

assessment

Normal

CTG

Offer IA if

lo

w risk or

recommend

CEFM if

risk factors

Recommend

CEFM,

intr

avenous

antibiotics,

careful

observation

of CTG

Recommend

CEFM and careful

surveillance for

signs of infection

CEFM, intravenous

antibiotics, consider

probability and timing

of spontaneous

delivery

Suspicious

CTG

Recommend

CEFM,

intr

auterine

resuscitation

measures

and observe

carefully

Recommend

CEFM,

intr

avenous

antibiotics

Recommend

CEFM, reconsider

risk of infection

and delivery if

vaginal birth is not

immin

ent

CEFM, intravenous

antibiotics, assisted

delivery unless

spontaneous delivery

immin

ent

Abnormal

CTG

Recommend

CEFM,

intr

auterine

resuscitation

Recommend

CEFM,

intr

avenous

antibiotics

delivery if

vaginal

delivery is not

immin

ent

Recommend

CEFM, or delivery

depending on the

probability of

spontaneous

delivery, reconsider

risk of infection

CEFM, intravenous

antibiotics, urgent

assisted delivery by Csection or assisted

vaginal delivery unless

delivery immediately

immin

ent

Caution: Additional tests of fetal well-being such as fetal scalp blood sampling (FBS) and

fetal ECG (ST-Analyser) are not useful in predicting MAS. In addition, scientific evidence

suggests that FBS can provide a false-positive result as meconium contains bile acids which

alter the pH of fetal scalp sample due to contamination.

Thin meconium does not alter the way CEFM should be interpreted, as in the

majority of cases it will be of physiological aetiology. The possibility of

infection should be considered and if there is any possibility ofchorioamnionitis, then monitoring should be managed as if meconium were

heavy.

CEFM showing a suspicious type pattern usually indicates a fetus that is under

stress, either a mechanical one (cord compression decelerations) or a possible

infection (an uncomplicated tachycardia) with risk of developing hypoxia.

Urgent clinical review with interventions to improve the fetal condition is

implemented (intravenous fluids and optimization of maternal position). The

interplay of sepsis, meconium and hypoxia must be considered along with the

likelihood that fetal stress can be effectively reduced and the expected interval

until spontaneous delivery. Care must be individualized, but a decision to

recommend immediate delivery by C-section should be considered in cases with

abnormal monitoring and possible sepsis where spontaneous delivery (or

assisted vaginal delivery) is not imminent. If the decision is made to continue,

then continuous FHR monitoring should be performed as fetal hypoxia may

develop faster in the presence of meconium. Where possible, clinical decisions

should be made to avoid deterioration of such a trace to become pathological. A

true reduction in baseline variability (<5 bpm) or development of saltatory

pattern on a previously ‘suspicious’ CTG trace would be particularly ominous in

the circumstance and should be managed without delay as a pathological trace.

CEFM showing a pathological type pattern with a much greater risk that the fetus

has significant hypoxia (usually a complicated baseline tachycardia but

occasionally reduced variability on an admission CTG of a woman in labour

with thick meconium) requires delivery to be expedited by C-section or assisted

vaginal delivery. A senior clinician should be involved in the decision-making

process with clear documentation of the thinking behind the decision. It is

important to appreciate that additional tests of fetal well-being such as FBS and

fetal ECG (ST-Analyser or STAN) are not useful in predicting MAS. FBS may

give a false-positive result as the presence of bile acids in meconium may

reduce the pH of scalp blood sample.

Increased baseline FHR and presence of repeated atypical or prolonged

decelerations indicative of ongoing hypoxia may increase the likelihood ofCommon Pitfalls

Consequences of Meconium

MAS.

In cases of MSAF with a gestation <37 weeks, immediate CEFM and urgent

review by a senior obstetrician to formulate a plan for delivery are

recommended. Any abnormality in FHR monitoring or evidence of sepsis

requires consideration of expediting delivery by C-section unless vaginal

delivery is imminent. FBS is not recommended as a lack of fetal reserve in the

premature fetus and an increased likelihood of infection in combination with

meconium is a situation when the rate of development of hypoxia is

unpredictable.

Failure to recommend monitoring in women with risk factors for hypoxia or

infection presenting with MSAF.

UK guidelines for the interpretation of CEFM do not make specific

recommendation about how interpretation should be altered by the finding of

significant meconium.

Not considering infection risks when formulating a management plan for a labour

complicated by meconium.

Delaying delivery in the presence of developing hypoxia with the risk of fetal

gasping in utero.

Cerebral palsy is twice as common in term infants with MSAF than in infants

with clear fluid. In preterm labour, it is an even higher risk factor for future

neurologic disorder with one study showing that 41 per cent of premature infants

born with MSAF develop cerebral palsy, compared to 10 per cent of preterm

infants with clear amniotic fluid.Further Reading

Hofmeyr GJ, Xu H, Eke AC. Amnioinfusion for meconium-stained liquor in labour.

Cochrane Database Syst Rev. 2014; 1.

National Institute for Health and Care Excellence. Intrapartum care: care of healthy women

and their babies during childbirth. Clinical guideline 55. 2007.

National Institute for Health and Care Excellence. Intrapartum care: care of healthy women

and their babies during childbirth. Clinical guideline 109. 2014.

Siriwachirachai T, Sangkomkamhang US, Lumbiganon P, Laopaiboon M. Antibiotics for

meconium stained amniotic fluid in labour for preventing maternal and neonatal infection.

Cochrane Database Syst Rev. 2014; 11.