History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include: gestational age >42 weeks; maternal history of hypertension, pre-eclampsia, eclampsia, smoking, substance abuse; fetal distress; oligohydramnios; thick meconium; an Apgar score <7; chorioamnionitis and caesarean delivery.

signs of post-maturity

Typical signs include green/yellow-coloured skin and umbilical cord; long, stained nails; dry and peeling skin; post-mature appearance; and loss of subcutaneous tissue.

tachypnoea

Usually seen immediately after birth. However, a significant number of infants may be asymptomatic and apparently vigorous at birth and develop severe respiratory distress hours later.

cyanosis

Usually seen immediately after birth. However, a significant number of infants may be asymptomatic and apparently vigorous at birth and develop severe respiratory distress hours later. The presence of cyanosis should prompt immediate intervention.

chest wall asymmetry with decreased air entry

An asymmetric chest wall and asymmetric movements with decreased air entry suggest pneumothorax.[Figure caption and citation for the preceding image starts]: CXR showing air at the base of right lung above the diaphragm, suggestive of pneumothorax in a patient with MASFrom the personal collection of Dr Vidyasagar and Dr Bhat [Citation ends].com.bmj.content.model.Caption@729dec49

barrel-shaped chest

Seen as increased anteroposterior chest diameter.

Other diagnostic factors

common

grunting

Due to reduced pulmonary compliance.

chest retractions

Due to reduced pulmonary compliance.

rales

Breath sounds may be diminished. Diffuse rales may be present.

rhonchi

Breath sounds may be diminished. Rhonchi may be present.

tachycardia

May be present due to respiratory distress.

hypotension

May be present due to respiratory distress.

Risk factors

strong

gestational age >42 weeks

Meconium-stained amniotic fluid is seen in 22% to 44% of post-mature babies (>42 weeks' gestation).[3] Post-maturity is associated with increasing placental insufficiency, which causes fetal hypoxia and passage of meconium. The reported decreased incidence of MAS during the 1990s may be due to a 33% reduction in post-term births.[8]

pregnancy-induced hypertension

Pregnancy-induced hypertension is associated with a 1.7-fold increased risk of MAS.[26]

maternal diabetes mellitus

Maternal diabetes mellitus is associated with a 3-fold increased risk of MAS.[26]

maternal smoking or substance misuse

Maternal tobacco smoking and substance misuse (especially cocaine) are associated with fetal distress and an increased risk of meconium-stained amniotic fluid and MAS.[6] They can cause placental vasoconstriction, which leads to fetal hypoxia and induces fetal passage of meconium. 

fetal distress

Meconium passage is a marker of intrapartum and antepartum fetal compromise. Non-reassuring or abnormal cardiotocography is associated with MAS.[27]

oligohydramnios

Causes cord compression and fetal hypoxaemia. Oligohydramnios is associated with a 2.8-fold increase in risk of MAS.[28]

thick meconium

Clinical presentation of infants born in meconium-stained amniotic fluid can depend on the consistency of the meconium. When infants are born through thin meconium and are vigorous at birth, respiratory complications are minimal.[29]

Apgar score <7

Apgar score <7 at 1 minute is associated with increased risk of MAS in babies admitted to the neonatal unit.[27] Low 5-minute Apgar score is associated with increased risk of MAS requiring intubation.[30]

chorioamnionitis

Causes fetal stress and passage of meconium in utero. Intrapartum maternal fever is associated with diagnosis of MAS.[27]

caesarean delivery

Babies born by caesarean section have a greater risk of MAS.[27]

weak

black ancestry

Black newborns are 1.54 times more likely to have MAS with symptoms compared with white newborns.[7]

male sex

Male infants are at higher risk.[7]

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