Effects of epidurals on the newborn

The effect of regional (epidural, spinal, combined spinal analgesia) analgesia on the newborn has been extensively investigated. It carries both potential benefits and potential risks to the fetus. The overall effect is to neither harm nor help the unborn child.

Potential benefits

Severe pain, when experienced by a woman in labour, may result in a stress response. Despite there being pronounced differences in the philosophy and technical application of the various methods of pain relief in childbirth, many have made a similar observation - that stress can interfere with the normal progress of labour and it can increase the perception of pain. The effects of stress in the mother, may in addition, be transferred to the fetus.

Any technique used during labour which decreases the mother’s stress should be of benefit to the child. Epidural analgesia has been demonstrated to have this effect.

Under conditions of stress, the body produces substances into the circulation and from nerves called catecholamines: adrenaline (epinephrine) and noradrenaline (norepinephrine). These have effects which may improve the body’s ability to deal with the stress. For instance: increasing the heart rate and improving blood flow to contracting muscles allows one to flee to safety faster. This is called the ‘fight or flight’ response. It is a nonspecific response and has a variety of triggers. As a result the benefit to be gained from it will vary. For example: catecholamines will be released in a person who has suffered from blood loss. It may be life saving in this event.

Catecholamines released during labour as a result of pain or anxiety will be of little benefit to the mother or fetus under normal conditions. Circulating adrenaline can diminish the strength and synchrony of the uterine contractions. ‘Dyscoordinate’ labour may ensue because the cervix dilates much more slowly. Much research has addressed the effect of epidurals on the progress of labour. The paradoxical ‘speeding-up’ of a poorly progressing labour which has been observed has been attributed to a reduction in production of these catecholamines by the mother when effective pain relief is achieved.

Stress also tends to make people over-breathe. Over-breathing during labour can cause excessive amounts of carbon dioxide to be breathed out resulting in an imbalance of the mother’s acid-base (pH) balance. She may become alkalotic. This may reduce the delivery of oxygen to the fetus. Excessive catecholamines may also do this. When insufficient oxygen is being delivered to the fetus, it mounts a similar stress response. In the fetus, the stress response will be caused by asphyxia. We can monitor the fetus for signs of stress in a number of ways. An increase in the fetal heart rate, a characteristic pattern on the cardiotocograph trace or the appearance of fetal stool in the liquor (meconium) are examples of these.

Epidural analgesia has been demonstrated to be of benefit in some labours because it normalizes the levels of cathecholamines and the mother’s breathing pattern. The mother relaxes, uterine contractions regain their effectiveness and there are less stress signs of stress by the fetus. These effects, however, are by no means predictable.

Epidurals also have the potential to cause stress to the fetus. It is generally considered that they will not have this effect if the epidural is properly managed. The levels of local anaesthetic and opioid drugs in the mother’s blood during routine epidural analgesia do not have any adverse effects on the fetus. The infant is not born ‘doped and unresponsive’, for example. If the mother suffers a problem with the epidural, for example, severe hypotension, then the condition of the fetus may be compromised.

The delivery of oxygen to the fetus is determined by the concentration of oxygen in the mother’s blood and the blood flow to the placenta.

The concentration of oxygen in the mother’s blood may decrease if she is heavily sedated. As explained in the section on opioids and the newborn, there is no reason why this should occur during labour. It may occur if the level of the epidural block rises high enough to weaken her respiratory muscles. This is a potential problem with anaesthesia for caesarean section where higher concentrations of local anaesthetic are needed. The dilute solutions used for labour make this a rare (and treatable) complication in this setting. Finally, an inadvertent injection of a large amount of local anaesthetic may cause the mother to fit. This would also threaten delivery of oxygen to the fetus. This is also a rare complication.

A severe (and untreated) fall in the mother’s blood pressure may decrease blood flow to the placenta such that the delivery of oxygen to the fetus is inadequate. Supine hypotension may occur when an epidural is in progress, and this is why it is important for the mother to either lie on her side or with one hip ‘wedged’ up on a pillow.