Fetal breathing in labor.

Fetal breathing during labor was investigated in a 3-part study of 42 normal singleton pregnancies. In the first part fetal breathing movements (FBM) were compared antenatally and during labor in 22 patients to determine whether FBM persisted during labor in fetuses in whom these movements had been demonstrated antenatally. In the second part a double-blind trial was conducted on the responsiveness of fetal breathing in labor to maternal glucose infusion in 12 patients. In the third part the influence of artificial rupture of the membranes (ARM) to induce labor was examined in 8 patients. Fetuses spent 36% of their time making breathing movements antenatally but this decreased to less than 1% during labor. Fetal trunk movements also decreased during labor but not significantly. Fetal breathing and trunk movements were not stimulated by maternal glucose infusion. Fetal breathing but not trunk movements were significantly inhibited by ARM prior to the onset of labor. Cessation of fetal breathing in labor is normal, but the cause of this change in behavior has not been positively identified.