Physiological changes in pregnancy affect the volume, acidity and emptying of gastric secretions as well as sphincter mechanisms in the lower oesophagus. Interventions in labour such as analgesia may also affect these changes adversely. General anaesthesia is occasionally necessary in emergency situations, and the presence of a full stomach (and thus the risk of aspiration of gastric contents) should always be assumed in such patients (see Chapter 59, Aspiration of gastric contents). The increasing incidence of obesity in the pregnant population has raised concerns that these patients may be at more risk of aspiration should they need a general anaesthetic for operative delivery.
Problems and special considerations
Increased circulating progesterone associated with pregnancy relaxes smooth muscle and causes relaxation of the lower oesophageal sphincter, whereas placental gastrin increases the volume and decreases the pH of gastric contents. The enlarging uterus increases intragastric pressure and there is an increase in small and large bowel transit time. However, evidence suggests that gastric emptying per se is not affected by pregnancy, although it may be decreased in labour if opioids are given.
Epidural analgesia with local anaesthetic solutions in labour is associated with normal gastric emptying, whereas subarachnoid or epidural opioids (fentanyl or diamorphine) in large doses cause a modest decrease in gastric emptying. Systemic opioid analgesia causes a much greater and prolonged decrease in gastric emptying. There are some randomised trials that have demonstrated large gastric volumes and a high incidence of vomiting in women allowed to eat solid food, even when pain was adequately controlled with a low-dose fentanyl/bupivacaine epidural. Previous studies suggested that oral intake of food during labour may be associated with a longer duration of labour and also possibly an increase in caesarean section rate, but recent evidence suggests that this is not the case.
The risk of gastroesophageal reflux is considerably reduced within 48 hours of delivery, owing to the decreasing progesterone level and the relief of raised intra-abdominal pressure. Nevertheless, the period of risk of aspiration extends to a poorly defined time after delivery, and appropriate general anaesthetic management in the early postpartum period remains somewhat controversial.
Routine withholding of food and fluids in labour has been challenged by a number of authors, particularly those who are not anaesthetists. They point out that absolute starvation is not popular with mothers, that aspiration associated with emergency general anaesthesia nowadays is uncommon owing to the increase in use of regional anaesthesia, and that there may be risks associated with prolonged starvation. On the other hand, there is little evidence that a period of starvation during labour is harmful, although it may be unpleasant. Starvation is associated with ketosis, but this has not been found to affect the duration or outcome of labour.
Management options
There are three approaches to the treatment of feeding in labour. The traditional approach is to assume that all women in labour are at risk of an event that will require emergency general anaesthesia, and that they are therefore at risk of aspiration of large volumes of acid gastric contents. As a consequence of this assumption, all women in labour are starved, allowed only sips of water to drink and given regular H2-antagonists and antacids (see Chapter 59, Aspiration of gastric contents). This regimen has become less common in recent years for the reasons discussed above. In addition, women who know that a unit’s policy is not to allow any oral intake are more likely to ‘binge’ before admission in labour, potentially negating any benefit from the policy.
Another approach is to assume that women in labour require food and fluid and to give these liberally. Often no H2-blockers are given. A more rational approach is to stratify management on the basis of risk factors such as morbid obesity, upper gastrointestinal tract abnormalities or an increased likelihood of operative intervention. Current guidance from the National Institute for Health and Care Excellence (NICE) recommends that parturients should be advised that they may consume a light diet during labour unless they have received opioids or they become at a higher risk of receiving general anaesthesia. H2- receptor antagonists should be considered for the higher-risk group. For those who do eat and drink during labour, substances that are associated with slower gastric emptying (those with high fat or sugar content) should be discouraged in favour of low-residue foods and isotonic drinks.
If intravenous water is required in labour, the most sensible fluid to provide might be 5% or 10% dextrose. Unfortunately, this has been associated with fluid overload in the mother and hyponatraemia in the neonate. However, modest volumes (< 1 litre) do not significantly affect neonatal plasma sodium concentrations. Many units give relatively low volumes of intravenous saline, dextrose-saline or Hartmann’s solution when intravenous fluid is considered necessary.
Key points
• Solid food ingested during labour is not predictably absorbed.
• Women treated with epidural analgesia may have normal gastric emptying unless large boluses of opioid are given.
• Opioids given parenterally markedly decrease gastric emptying.
• Acid aspiration prophylaxis should be given to all women at risk of intervention in labour.
Further reading
National Institute for Health and Care Excellence. Intrapartum Care for Healthy Women and Babies.
Clinical Guideline 190. London: NICE, 2014 (updated 2017). www.nice.org.uk/guidance/cg190 (accessed December 2018).
O’Sullivan G, Liu B, Hart D, Seed P, Shennan A. Effect of food intake during labour on obstetric outcome: randomised controlled trial. BMJ 2009; 338: b784.
Singata M, Tranmer J, Gyte GM. Restricting oral fluid and food intake during labour. Cochrane Database Syst Rev 2013; (8): CD003930.
Sperling JD, Dahlke JD, Sibai BM. Restriction of oral intake during labour: whither are we bound? Am J Obstet Gynecol 2016; 214: 592-6.