Can acute inflammation in the placental membranes, amniotic fluid, or both, predispose to the development of abnormal fetal heart rate patterns? One hundred cases in which bradycardia was noted were compared with 48 cases in which abnormal fetal heart rate patterns did not occur. Case and control subjects were matched to provide an equivalent risk of developing ascending infection in the two groups. Fetoplacental weight ratio and the presence of other placental diseases were also considered. The presence of acute inflammation in the umbilical cord (p = 0.03), amnion (p = 0.01), and choriodecidua (p = 0.03), and higher grades of inflammation in chorionic plate (p = 0.03) were linked to the presence of abnormal fetal heart rate patterns. No other placental factors were associated with increased risk of fetal bradycardia. The association of abnormal fetal heart rate patterns with acute inflammation suggests that intra-amniotic inflammation is important in the genesis of fetal bradycardias. The inflamed amniotic fluid could alter fetal metabolism via effects on the pulmonary or gastrointestinal systems or effects on umbilical and chorionic vessels.