In the general population, diabetes mellitus is present in about 2% of individuals, about half of them undiagnosed. In pregnancy, insulin requirements increase as peripheral sensitivity to insulin decreases (thought to be caused by the opposing action of placental hormones). Thus patients known to have diabetes may become unstable, and otherwise normal subjects may reveal themselves as having gestational diabetes if they cannot meet the increased demands (the latter occurs in up to 2-5% of pregnancies). Most women who develop gestational diabetes recover after pregnancy, although most relapse in subsequent pregnancies at an earlier gestational age, and there is a 50% risk of developing type 2 diabetes in later life.
Current UK guidelines recommend screening for gestational diabetes using the oral glucose tolerance test (OGTT) in pregnant women with risk factors, which include a history or family history of gestational diabetes, raised body mass index (BMI), or previous macrosomic baby. The OGTT includes the administration of 75 g glucose orally, followed by blood glucose measurement after 2 hours. The test is offered at 24-28 weeks’ gestation but should be performed earlier in women with a history of gestational diabetes and repeated if the initial results are normal.
Problems and special considerations
Effect of diabetes on the mother
Diabetes has many effects on most organ systems, the most immediately important being renal impairment, cardiovascular disease and central and peripheral neurological disease. Women with long-standing type 1 diabetes, depending on their overall glycaemic control, may already manifest these complications, whereas those women with gestational or type 2 diabetes are usually younger than 40-45 years and systemic effects tend to be less common.
Control of blood sugar
This is important during pregnancy, since poor control is associated with an increased incidence of fetal abnormalities (see below). In pregnancy, insulin requirements increase by up to 50% at term. During labour, it is important to avoid hyper- or hypoglycaemia, the former because it results in maternal and fetal acidosis and the latter because of the risk of impaired neurological function. Insulin requirements may decrease in the first stage but increase in the second stage of labour, although this may depend on other factors such as length of labour, prelabour state, etc.
Effect of diabetes on pregnancy
Women with diabetes have an increased incidence of miscarriage, pregnancy-induced hypertension, polyhydramnios, fetal macrosomia, obstructed labour, caesarean section and preterm labour (the last may not hold for gestational diabetes). There is also an increased incidence of neonatal hypoglycaemia and hyperbilirubinaemia. In type 1 diabetes, there is a 5- to 10-fold incidence of congenital malformation if glycaemic control during pregnancy is poor, with a 5-fold increase in stillbirth rate and 4- to 5-fold increase in perinatal death rate. Good glycaemic control reduces the incidence of congenital malformation to 2%, about twice the normal.
Management options
Before conception, women known to have diabetes should be counselled and their care optimised (ideally, glycosylated haemoglobin concentration < 6.5%).
During pregnancy, careful dietary advice, and possibly also pharmacological intervention, aims to maintain normal blood glucose concentrations. Ideal glucose levels are below 5.3 mmol/l fasting, 7.8 mmol/l 1 hour postprandial and 6.4 mmol/L 2 hours postprandial. Close follow-up of diabetic pregnant women is required, with monitoring of glycaemic control as well as screening for infections, since diabetic ketoacidosis may be precipitated by infection, as in the non-pregnant state. It has been recommended that diabetic pregnant women with comorbidities such as obesity or autonomic neuropathy be reviewed by an anaesthetist in the third trimester of their pregnancy.
Increasing insulin requirements in pregnancy may reflect reduced placental function and may be an indication for induction of labour. Women with absent warning signs of hypoglycaemia should be advised against driving (pregnancy may alter awareness of hypoglycaemia, which occurs particularly in the first trimester). With regard to the fetus, women with diabetes should be offered a detailed fetal cardiac scan at 20 weeks’ gestation.
During labour, most authorities advocate continuous glucose/insulin infusions; a suitable regimen comprises a 5% glucose infusion plus 20 mmol/l potassium chloride with a continuous insulin infusion using a sliding scale, according to regular (30-60-minute) blood glucose concentration monitoring (Table 102.1). The aim is to maintain blood glucose concentrations at 4-7 mmol/l; if this cannot be achieved the entire insulin infusion scale is increased by 1 U/h. If blood glucose concentration repeatedly falls below 4 mmol/l, the 5% dextrose may be changed for 10% glucose. Urine should be tested, e.g. 4-hourly, for glucose and ketones. Avoidance of glucose during labour has been popular previously, but leads to maternal and fetal acidosis. Most authorities advise continuous fetal monitoring throughout labour, and a paediatrician should attend all deliveries, with neonatal unit admission prepared. For elective caesarean section, the same intravenous regimen is started in the morning, the patient having been nil-by-mouth since midnight and having omitted her usual morning insulin.
Table 102.1 Sample sliding scale for insulin during labour in diabetic women
|
Blood glucose concentration (mmol/l) |
< 3.9 |
4.0 5.9 |
6.0 8.9 |
9.0 11.9 |
12.0 14.9 |
15.0 17.9 |
> 18.0 |
|
Insulin infusion rate (U soluble insulin/h) |
0.5 |
1 |
2 |
3 |
4 |
5 |
6 |
Insulin requirements fall rapidly once delivery has occurred, and the insulin infusion rate should be halved once the baby has been born. Most women with gestational diabetes do not need insulin postpartum; insulin-dependent diabetic patients may be given a subcutaneous dose of soluble insulin (e.g. 5 U) when ready to eat and drink, and the infusion stopped 60 minutes later.
Management as far as regional or general anaesthesia is concerned is along standard lines, although the former is especially desirable. In labour, regional analgesia is thought to be beneficial by reducing catecholamine levels and thus avoiding anti-insulin effects and the propensity for acidosis. Care should be taken to assess the mother for the complications of diabetes, as above. In addition, of especial relevance to general anaesthesia, autonomic neuropathy may be associated with reduced gastric emptying, and a syndrome of stiff joints has been described in which difficult tracheal intubation has featured. The syndrome is suggested by the ‘prayer sign’ in which the patient is unable to lay the palmar surfaces of her index fingers fully flat against one another when pressing her palms together as if praying; when viewed from the side there is a space between the proximal phalangeal joints. The syndrome has also been implicated in causing reduced compliance of the epidural space, with the risk of spinal cord ischaemia when large volumes are injected epidurally.
Fluid therapy should be separate from intravenous dextrose/insulin; thus two intravenous cannulae are usually required if anaesthetic intervention is needed. Hartmann’s solution may result in a small increase in blood glucose concentration caused by gluconeogenesis from lactate metabolism, although this is rarely a problem in practice. Patients should receive adequate diabetic follow-up postpartum. Patients who have presented with gestational diabetes in particular should be followed up with a 6-week fasting plasma glucose check, and this should be checked annually thereafter.
Diabetic ketoacidosis in pregnancy is a rare but potentially life-threatening complication that may occur in up to 3% of pregnant women with diabetes. Principles of management are as for non-pregnant patients, namely removal of the trigger, fluid resuscitation, and the correction of hyperglycaemia and metabolic derangements such as acidosis and hyperka- laemia. Particular attention must be paid to the optimisation of fetal oxygenation and the stabilisation of maternal condition before proceeding with a caesarean section for fetal indications.
Key points
• Diabetes mellitus is associated with increased incidence of fetal malformations, macrosomia and death, especially if diabetic control is poor.
• Regional analgesia and anaesthesia are especially desirable.
• Insulin and glucose infusions are used in labour.
• Insulin requirements fall rapidly after delivery.
• Diabetic ketoacidosis is rare in pregnancy but can carry significant maternal and fetal morbidity.
Further reading
Association of Anaesthetists of Great Britain and Ireland. Peri-operative management of the surgical patient with diabetes 2015. Anaesthesia 2015; 70: 1427-40.
de Veciana M. Diabetes ketoacidosis in pregnancy. Semin Perinatal 2013; 37: 267-73.
McCance DR. Diabetes in pregnancy. Best Pract Res Clin Obstet Gynaecol 2015; 29: 685-99.
National Institute for Health and Care Excellence. Diabetes in Pregnancy: Management from
Preconception to the Postnatal Period. NICE Guideline NG 3. London: NICE, 2015. www.nice.org .uk/guidance/ng3 (accessed December 2018).