Effects of intravenous meperidine and meperidine with promethazine on uterine activity and fetal heart rate during labor.

A prospective study of the effects of the i.v. injection of 75 mg meperidine, alone or combined with 25 mg promethazine, was conducted by continuous and direct monitoring of the fetus and of intrauterine pressure. The study was carried out in 16 primiparas and 24 multiparas in active spontaneous labor with cervical dilatation of 3 to 4 cm. Administration of meperidine and of meperidine with promethazine was associated with an increase in uterine activity of 31 to 45% (Montevideo units), respectively. The most marked effects were on the amplitude of the uterine contractions. There was no significant change in uterine tone. A tetanic response was recorded in two patients who vomited after the administration of meperidine with promethazine and was followed by slowing of the fetal heart rate. In no other cases were there significant changes in fetal heart rate. Except for the latter two patients, no adverse effect of meperidine or of meperidine with promethazine on the fetal heart rate was noted. The condition of the newborns at birth was excellent in all but three cases, in two of which maternal amniotic infection and high fever were present.