Epidemiology

MAS is a serious complication associated with meconium-stained amniotic fluid (MSAF).

MSAF occurs in 7% to 22% of term deliveries, with higher rates (22% to 44%) in post-term deliveries (>42 weeks).[3] It is uncommon (<5%) in deliveries at <34 weeks' gestation, likely due to immature gut peristalsis.[1] Black or South Asian ethnicity, vaginal breech delivery, and increasing gestational age all increase the risk of MSAF.[4]

MSAF is classified according to consistency as thick or thin meconium. About 1% of babies are born through thin meconium and 7% are born through thick meconium.[5]

Between 2% and 9% of babies born through MSAF develop MAS.[6]

Incidence of MAS with symptoms was 2.49 cases per 1000 births in the US in 2012.[7] A further 1.15 per 1000 newborns had MAS without symptoms. Black newborns were 1.54 times more likely to have MAS with symptoms compared with white newborns.[7] Population studies from the US, Australia, and France show that the frequency of MAS and MSAF has steadily decreased over the last decades.[8][9][10][11]

The diagnosis of MAS increases with increasing gestational age, from 1.3% at 38 weeks to 4.8% at 42 weeks.[12]

Over 81% of infants with MAS are discharged home, 9% are transferred to higher levels of neonatal intensive care, 5.5% are transferred to another clinical service within the same hospital, 1.2% die, and 1.4% are treated or transferred for extracorporeal membrane oxygenation (ECMO).[9] Survival of babies with MAS who undergo ECMO has been reported as 94%.[13]

Meta-analysis has shown that labour induction for term or post-term pregnancies results in fewer cases of MAS and reduced perinatal mortality compared with expectant management.[14][15] [ Cochrane Clinical Answers logo ]

MSAF and MAS incidence and mortality are far higher in developing countries.[16][17]

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