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Objective: This study was undertaken to evaluate whether the administration of meperidine decreases the length of labor in patients with a diagnosis of dystocia during the first stage of labor., Study Design: Women with term singleton pregnancies who received a diagnosis of dystocia and required an active management of labor were randomly assigned to receive either 100 mg of meperidine or placebo. The primary outcome measure was length of labor., Results: Four hundred seven pregnant women were included. There were no significant statistical differences between meperidine and placebo groups in length of labor and operative delivery rates such as forceps and cesarean section by intention-to-treat analysis. Low Apgar scores, umbilical artery acidosis, and admission to neonatal care units were increased in the meperidine group., Conclusion: Because of the absence of any benefits in patients with dystocia in labor and the presence of harmful effects on neonatal outcomes, meperidine should not be used during labor for this specific indication.

Although meperidine appears to be the safest obstetric analgesic agent, it has been associated with infant respiratory depression in certain situations. It would appear that the incidence of fetal depression related to meperidine is dependent on the time of injection prior to delivery, the quantity of drug administered, and the rate of maternal metabolism of the analgesic. Previous work showed that meperidine is metabolized in the maternal system by one of three patterns. The present study demonstrates that the particular maternal serum pattern is characteristic for the individual, regardless of whether the patient is pregnant or not, and that the fetal depression, although usually mild, can be correlated with fetal pH data as well as Apgar scores. In addition, this study supports indirectly the contention that metabolites of meperidine rather than the parent compound cause fetal depression. It would appear, therefore, that in certain obstetric cases with a higher probability for infant depression, other analgesic agents might be considered, especially if the serum pattern indicates meperidine is being metabolized.

The effect of maternal labor, and fetal characteristics upon fetal heart rate behavior during the intrapartum period has been studied in 400 patients. Abnormal labor in comparison to normal labor has a higher baseline fetal heart rate with an increased incidence of baseline tachycardia and an increased incidence of absent or decreased baseline variability. A decreasing fetal weight gestational age percentile is associated with an increased incidence of variable decelerations. Segmental epidural and Demerol analgesia carefully administered has little effect upon fetal heart rate behavior.

Neurobehavioral evaluations were conducted in neonatal monkeys (Macaca mulatta) exposed to narcotic analgesics during labor through their dams. Infants exposed to meperidine (2 mg/kg maternal dose) or alfentanil (0.1 mg/kg maternal dose) were compared with controls whose dams received no analgesic. Meperidine and alfentanil differ in pharmacologic properties related to maternal-fetal transfer and neonatal metabolism. Drug-exposed infants showed neurobehavioral effects over the first 3 days of life including depressed respiration (at birth), depressed environmental response to aversive stimuli (days 0, 1, and 2), more overnight sleep (day 1), and more quiet behavior patterns while awake (day 3). In addition, drug exposure was associated with increased elicited muscle tone early in the neonatal period and earlier maturation of sitting, standing, and walking. No effects on growth or health were noted, but drug-exposed infants had lower hematocrits and an earlier onset of a linear growth rate as reflected in body weight. No qualitative or quantitative differences were noted between the two drug treatments. Because behavioral effects were seen after the drug was eliminated, a direct pharmacologic action of the drug does not fully explain the findings.

Plasma epinephrine and norepinephrine concentrations during labor and immediately after delivery were compared to those of the third trimester in 21 uncomplicated pregnancies of married primigravid women, 20 to 32 years old. Third-trimester catecholamine concentrations were similar to those of normal, nonpregnant subjects; samples were obtained under identical conditions. Compared to third-trimester levels, significant elevations of plasma epinephrine and norepinephrine were found in three phases of labor (at 3 to 5 cm. and 9 to 10 cm. of cervical dilatation and immediately after delivery). Epinephrine values returned to normal within three to 21 minutes after delivery; norepinephrine values remained high or continued to rise in this time interval. Maternal analgesia and anesthesia influenced plasma catecholamine levels.