Meconium is the bowel contents of the fetus which has stained the amniotic fluid. In pre-term fetuses it is rare but is present in 30% of cases after 42 weeks (1).
If the meconium is old or dilute it is seldom significant but if it is thick or undiluted then it is often passed in response to hypoxia and then perinatal death is increased four-fold (1). A breech positioned baby may well lead to the observation of thick undiluted meconium but if the baby is cephalic oligohydramnios may be the cause and if the Cardiotocography (CTG) trace is suspicious the baby should be delivered (2)(3).
Because meconium can be passed under normal circumstances its presence or absence is not a reliable indicator. In addition the presence of the head in the pelvis might prevent it from being revealed as would a late amniotomy(1).
Caution is indicated if it is present however because:
If meconium is present Cardiotocography (CTG) is indicated (2).