Amnioinfusion does not reduce the risk of meconium aspiration syndrome

An international randomized trial, funded by the Canadian Institutes of Health Research (CIHR), has revealed that amnioinfusion, the infusion of saline into the uterus, does not reduce the risk of meconium aspiration syndrome (MAS), as previously believed.

The study, which is led by Dr. William Fraser from the Department of Obstetrics and Gynaecolgy of the Université de Montréal and the Maternal-Child Health Centre associated with Ste-Justine's Hospital, is published in the current issue of the New England Journal of Medicine.

"Dr. Fraser and his colleagues have made an extremely important contribution to our knowledge about the possible prevention of MAS, a rare but very serious neonatal lung condition," said Dr. Michael Kramer, Scientific Director of the CIHR Institute of Human Development, Child and Youth Health. "The rigorous study methods and international scope of this randomized trial (56 study sites in 13 countries) provides very strong evidence against the use of amnioinfusion, and the results are likely to have a major impact on childbirth practices around the world."

Meconium aspiration syndrome (also referred to as meconium aspiration) occurs when a newborn inhales a mixture of meconium and amniotic fluid during labor and delivery. Meconium is the material that fills the fetal intestinal tract during pregnancy and is formed from ingested amniotic fluid and dead intestinal cells. Although it is sterile, inhaled meconium is highly irritating to the lung when the infant takes its first breaths. It can cause a partial or complete blockage of the baby's airways when exhaling, making it difficult to breathe.

Meconium alters the amniotic fluid, reducing antibacterial activity and subsequently increasing the risk of perinatal bacterial infection. Aspiration induces 3 major pulmonary effects, which are airway obstruction, surfactant dysfunction, and chemical pneumonitis. Meconium-stained amniotic fluid occurs in 7 to 22% of term deliveries. In anywhere from 2% to more than a third of these deliveries, MAS can occur.

One of the techniques used to reduce its risk is amnioinfusion. This technique involves infusing saline, via insertion of a catheter in the uterine cervix, into the amniotic cavity of women in labour who show heavy meconium. Amnioinfusion is intended to reduce the risk of MAS by diluting the meconium.

Women were eligible for this randomized trial, after the fetal membranes ruptured and thick, opaque, meconium-stained (greenish colour) amniotic fluid was identified. In this trial, amnioinfusion was not effective in reducing the risk of meconium aspiration syndrome.

"Amnioinfusion has been used in the prevention of meconium aspiration syndrome, or MAS, for the past 15 years. Prior to our study, information about the effectiveness of the intervention was based on small studies carried out in single centers," said Dr. Fraser. "Our research is the first large study that has a sufficient sample size to answer the question as to whether the technique is effective to prevent MAS. We showed that it is not effective in this context. This trial did not examine amniofusion in other contexts. Thorough, large scale studies are needed before drawing conclusions on the potential role of amnioinfusion for other indications."

Dr. Fraser worked with collaborators in Canada, France (Dr. François Goffinet, from INSERM Unité149 and Maternité de Port-Royal), as well as with researchers from Argentina, Belgium, Brazil, Ireland, Mexico, Portugal, South Africa, Switzerland, Tunisia, the United Kingdom and Uruguay.