Uterine contractions at the end of pregnancy lead to dilatation of cervix and the expulsion of the fetus from the birth canal. Myometrial contractions are a very painful and unpleasant experience for mothers. The aim of the obstetrician is to decrease the length of labor and labor pains as much as possible by careful control of the phases of labor. In the case of severe labor pains resulting from uterine contractions, the administration of narcotic drugs such as pethidine (meperidine) 1 is indicated.
1Pain and anxiety can affect the progress of delivery by increasing the release of catecholamines and Cortisol. Noradrenaline increases uterine contractions while Cortisol and adrenaline decrease them. In many cases, severe labor pain and anxiety resulting from that can increase the release of adrenaline and Cortisol and lead to a decrease in contractions and consequently a prolonged labor.2 In some cases, pain and anxiety cause ineffective contractions. These contractions are severe with short intervals, but fail to have any progressive effect.2 Pethidine decreases the concentration of catecholamines in blood and by that means seems to increase the speed of delivery.
3Considering the effects of pethidine on cervical smooth muscle and on changes in cervical consistency, 4 as well as previous observations showing the effect of pethidine on the relief of labor pain, we decided to study parturients referred to the obstetrics and gynecology department at Kerman Medical Sciences University Hospital (Kerman, Iran) to obtain a more accurate picture of the effects of pethidine.
Patients and MethodsIn this randomized, double-blind clinical trial we sought to determine the effects of pethidine on relief of labor pain, uterine contractions and infant Apgar score. Case (pethidine-administered) and control groups (placeboadministered) were similar in mean age, length of time from marriage to pregnancy, job and place of residency. The required number of subjects, based on a pilot study and considering a power=90%, d=7% and error=5%, was determined as 44 in each group. Subjects were eligible for entry if they were primiparous, had a term-pregnancy (gestational age• 37 weeks), spontaneous labor pains, no narcotic addiction, not a high-risk pregnancy (e.g., preeclampsia, eclampsia, heart-respiratory problems or fetal distress), and at the start of the active phase of delivery (5-cm cervical dilatation) (2).Selected subjects were divided randomly into the case and control groups. The case group received 75 mg pethidine by intramuscular injection 1,3, 5-10 and the control group received the same volume (1.5 mL) of normal saline as a placebo. The first researcher injected patients at the beginning of the active phase (5-cm cervical dilatation). Before injection, the second researcher recorded the vital signs of the mother, including blood pressure, heart and respiratory rate, and the fetal heart rates, duration, and intervals of uterine contractions. The second researcher took the measurements again 45 minutes after injection of pethid...