Case 57: Glucose tolerance test

 

Case 57: Glucose tolerance test

CASE 57: GLUCOSE TOLERANCE TEST

History

A woman attends the antenatal day assessment unit to discuss the result of her glucose tolerance test. She is 42 years old and this is her sixth pregnancy. She has previously had three

caesarean sections, one early miscarriage and a termination of pregnancy. All booking tests

were normal as were her 11–14-week and anomaly ultrasound scans.

The woman is of Indian ethnic origin but was born and has always lived in the UK. She is

now 26 weeks’ gestation and her midwife arranged a glucose tolerance test because of a family

history of type 2 diabetes (her father and paternal aunt).

Examination

The body mass index (BMI) is 31 kg/m2. Blood pressure is 146/87 mmHg. The symphysiofundal height is 29 cm and the fetal heart rate is normal on auscultation.

INVESTIGATIONS

Urinalysis: glycosuria ++

Glucose tolerance test (75 g glucose drink):

Pretest fasting blood glucose: 6.4 mmol/L

2 h blood glucose following glucose load: 11.3 mmol/L

Questions

• What is the diagnosis and on what criteria can this be made?

• What are the principles of management for this patient?100 Cases in Obstetrics and Gynaecology

154

ANSWER 57

The diagnosis is of gestational diabetes mellitus (GDM) and is based on the 2 h glucose concentration exceeding 11.1 mmol/L (World Health Organization (WHO) criteria). The diagnosis may also be made if the fasting blood glucose exceeds 7.8 mmol/L, in which case a

formal glucose tolerance test would not have been necessary. Transient glycosuria is common

in pregnancy and may occur after a glucose-rich drink or snack. Therefore the urinalysis

alone is unhelpful in the assessment of this woman.

GDM occurs in up to 3 per cent of the pregnant population depending on the ethnic diversity

of the specific population. In some cases it may be the first presentation of previously undiagnosed diabetes.

! Risk factors for GDM

• Pre-existing:

• obesity

• previous GDM

• family history of diabetes

• women with previously large babies or stillbirth

• increasing maternal age

• Occurring in this pregnancy:

• glycosuria

• large for dates baby

• polyhydramnios

The importance of the diagnosis relates to the effect on the mother and fetus.

• Effects on the fetus:

• fetal macrosomia

• polyhydramnios

• neonatal hypoglycaemia

• neonatal respiratory distress syndrome

• increased stillbirth rate

• Effects on the mother:

• increased risk of traumatic delivery (e.g. shoulder dystocia)

• increased caesarean section risk

• increased risk of developing GDM in subsequent pregnancies

• 50 per cent increased risk of developing type 2 diabetes within 15 years

Management principles

• Optimal control of maternal blood glucose minimizes the chance of fetal complications. This needs the multidisciplinary input of a diabetologist, specialist diabetes

nurse, dietitian, specialist midwife and obstetrician.

• Dietary advice and counselling are the initial interventions (reduced fat and carbohydrate intake with weight control).

• Blood glucose monitoring at home should be initiated with pre- and postprandial

levels at each meal.

• Oral hypoglycaemics (metformin) may be used prior to commencing insulin in

women where diet control is not effective.Case 57: Glucose tolerance test

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• If blood glucose measurements are repeatedly high, insulin should be commenced.

• The fetus should be monitored with regular ultrasound scans for growth and liquor

volume (polyhydramnios being a sign of fetal polyuria secondary to excessive glucose level).

• Delivery should be planned by 40 weeks, but caesarean section should be performed

for obstetric indications only.

• Sliding-scale insulin should be initiated in labour for women on insulin.

• The insulin can be stopped immediately postpartum as normal glucose homeostasis

returns rapidly after delivery.

• The fetus should be carefully monitored for neonatal hypoglycaemia.

• The mother should have a repeat glucose tolerance test 6 weeks postpartum to rule

out pre-existing diabetes.

KEY POINTS

• Gestational diabetes should initially be treated with dietary and weight advice.

Insulin may be needed if blood glucose levels remain high.

• One-third of women with impaired glucose tolerance in pregnancy will go on to

develop diabetes mellitus in the next 25 y