The fetal gastrointestinal tract is exposed to melatonin and superoxide dismutase rich amniotic fluid throughout prenatal development.

Amniotic fluid (AF) is the first fluid to enter the gastrointestinal tract. Preterm birth is leading to a sudden interruption of AF swallowing. Understanding the composition of amniotic fluid is crucial to implement strategies preventing intestinal injury in preterm infants. We hypothesized that the fetal gastrointestinal tract (GIT) is exposed to melatonin and antioxidant enzymes via amniotic fluid throughout prenatal development. Amniotic fluid samples from 76 pregnant women with a median (range) gestational age of 38.0 (14.3-40.1) weeks have been collected. Immediately after birth blood samples were collected from the umbilical vein ( = 53). Median (Interquartile range) melatonin concentration was 30.5 pg/ml (12.7-118.3) and superoxide dismutase 1 (SOD1) concentration was 84 ng/ml (59-123). Extracellular glutathione peroxidase concentration was either not detectable or exceptionally low. We found a positive correlation between melatonin concentration in amniotic fluid and gestational age (Spearman's correlation coefficient,  = 0.570, <0.001), while SOD1 concentration in amniotic fluid was inversely correlated with gestational age ( = -0.246,  = 0.032). Compared to serum samples, melatonin concentration was statistically significantly higher in amniotic fluid (<0.001). Our results indicate that the fetal gastrointestinal system is continuously exposed to melatonin and SOD1 via the amniotic fluid throughout prenatal development.