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28. Meconium
28.1 Introduction
Meconium is the first intestinal discharge from newborns. It is a viscous, dark-green material composed of intestinal epithelial cells, mucus, lanugo and intestinal secretions (e.g. bile). The characteristic colour results from bile pigments, especially biliverdin. It also contains undigested debris from swallowed amniotic fluid. Meconium is sterile which differentiates it from stool.
Obstetrical teaching conventionally viewed meconium passage as a potential warning of fetal asphyxia. Moreover obstetricians have also long realized the prognostic dilemma of meconium. It occurs mostly in term and post-term pregnancies. It may be associated with fetal compromise but is also common in normal labours.
- (a)
Thick—viscous, tenacious containing large amount of particulate material.
- (b)
Thin—fluid is normal except for greenish colour.
- (c)
Moderate—if it is thicker and darker in colour.
- (a)
Grade I—MSL is translucent, light yellow-green in colour.
- (b)
Grade II—MSL is opalescent with deep green and light yellow in colour.
- (c)
Grade III—MSL is opaque and deep green in colour.
Thick MSL but not thin is associated with poor perinatal outcome [1, 2].
28.2 Incidence
Fetal passage of meconium before or during labour is common with incidence ranging from 12 to 20%. The incidence during labour increases with gestational age also—30% at 40 weeks and 50% at 42 weeks [3]. Presence of meconium below vocal cord is known as meconium aspiration. It occurs in 20–30% of all infants with meconium with approximately 12% mortality [4].
28.3 Pathophysiology
- 1.
Pathological explanation proposes that fetus pass meconium when hypoxia stimulates arginine vasopressin (AVP) release from fetal pituitary gland. AVP stimulates colonic smooth muscle to contract, resulting in intraamniotic defecation.
- 2.
Physiological explanation—meconium passage represents normal gastrointestinal tract maturation under neural control.
- 3.
Final theory suggests that meconium passage follows vagal stimulation from common but transient umbilical cord compression with resultant increased bowel peristalsis.
The effects of meconium in amniotic fluid are well reported [5]. Meconium decreases the antibacterial activity of amniotic fluid by altering levels of zinc which subsequently increases the risk of perinatal bacterial infection. Then, meconium acts as irritant to fetal skin and thus increases the incidence of erythema toxicum. Aspiration of meconium is the most severe complication before, during and after birth. It induces hypoxia via four major pulmonary effects: airway obstruction, pulmonary hypertension, chemical pneumonitis and surfactant dysfunction.
28.4 Causes
Risk factors promoting the passage of meconium in utero include the following:
Preeclampsia and eclampsia.
Placental insufficiency.
Gestational diabetes mellitus.
Post-term pregnancy.
Maternal chronic respiratory or cardiovascular diseases.
Drug abuse, especially tobacco and cocaine.
Chorioamnionitis/maternal infection.
Oligohydramnios.
Intrauterine growth restriction (IUGR).
Poor biophysical profile.
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