Nor does it reduce the risk of perinatal death or other major maternal or neonatal disorders in women in labor who have thick meconium staining of amniotic fluid.

Researchers studied almost 2,000 women from 56 centers in 13 countries. The women were enrolled during labor if they had thick meconium staining of amniotic fluid, a singleton fetus of at least 36 weeks' gestation presenting cephalically, ruptured membranes, a cervix dilated between 2 and 7 cm, and no indication for urgent delivery.

Perinatal death, moderate or severe meconium aspiration syndrome, or both occurred in 4.5% of the infants born to women in the amnioinfusion group, compared to 3.5% of those born to women in the control group (RR 1.26; 95% CI; 0.82–1.95). Rates of perinatal death and cesarean delivery were similar in both groups; five deaths occurred in each group, and 31.8% of the amnioinfusion group versus 29% of the control group required C-sections.

Researchers also looked at a subgroup of women who presented with a minimum of three variable decelerations in fetal heart rate during the 30 minutes prior to randomization, and found no benefit of amnioinfusion for this group either, but the analysis was underpowered.

An editorial in the same issue of the New England Journal of Medicine suggests that the failure of the procedure to prevent meconium aspiration syndrome may be the result of the fact that most infants in whom the syndrome develops have meconium in the tracheobronchial tree before presentation in labor, and dilution of meconium in amniotic fluid cannot address this problem.

Until we better understand the factors that influence when a fetal colon will pass meconium, the editorial concluded that the best way to reduce the incidence of meconium aspiration syndrome is to keep the rate of postterm delivery to a minimum.

Fraser WD, Hofmeyr J, Lede R, et al. Amnioinfusion for the prevention of the meconium aspiration syndrome. N Engl J Med. 2005;353:909-917.

Ross MG. Meconium aspiration syndrome—more than intrapartum meconium. N Engl J Med. 2005;353:946-948.