Used During Labor –Effects on the Baby

Systemic Analgesics Drugs Used During Labor –Effects on the Baby

There is no single ideal analgesic agent for use in labor. All analgesic drugs cross the placenta and depress the fetus. The degree of depression will depend on the dose of the drug the length of time of exposure and the maturity and well- being of the fetus.

                Although the opiates are the most effective analgesic drugs available, their use in obstetrics is losing favor because of the depressant effect on the neonate, the effect of the mother’s psyche, making her less aware of her experience of childbirth, and because in doses that minimize side effects the pain relief is poor.            

                The most commonly used opiate in labor is pethidine, although diamorphine and fetanyl are also used. The maternal side effects of narcotics are dose related and include hypoventilation, postural hypotension, postural pypotension and loss of consciousness. Emetic effects of all opiates are also dose-related but this varies in individual paticents. Grastric motility is decrease by narcotics and stomach emptying may b de3layed for up to 12 hours. Opiates are reported to shorten labor, and correct in co-ordinate uterine action. But the mechanism appears to be the relief of pain and anxiety rather than any direction action of the uterine muscle.

                Placental transfer of all the opiates takes place rapidly and equilibration between maternal and fetal blood is completed within a short time. The effects of ethidine on the fetus that can be demonstrated in utero are a decrease in beat-to-beat variability on the cadiotocograph and altered fetal electroencephalogram. The neonatal effects of maternal opiates are a decrease Apgar score, a prolonged time to achieve regular respiration, lower oxygen saturation, decreased minute volume, hypercapnia and abnormal neurobehavioural scores. All these effects are related and can persist in the neonate for several days since the half-life of the opiates in the neonate is four to five times longer than that in the adult.

 Opiate effects and side effects can all be antagonized by naloxone –a pure opiate antagonist. There is no purpose in giving any combination of opiate plus antagonist to the mother in pain, as all the actions, including the analgesic action, will be reserved. If the mother has received opiates in labor naloxone should be given to those neonates who are depressed and do not breathe following initial resuscitation.