Diabetes Mellitus: Management of Gestational Diabetes

• Diagnosis

• First visit after diagnosis

• Glycaemic control

• Subsequent visits

• Delivery

• Follow-up

• Management of Hypoglycaemia (clinical algorithm)

• References

Diagnosis

Routine screening

• All women (others than those at special risk see below) have a 75 g non-fasting glucose challenge test (GCT) performed at 26 weeks. If the 1-hour plasma glucose is ≥ 8.0 mmol/L, they will be recalled to have an oral glucose tolerance test as soon as possible. This is co-ordinated by the outpatient midwives on the basis of results received from pathology. Responsibility for screening and follow-up of women with abnormal glucose challenge tests ultimately rests with the woman’s home Team.
  
  

• The glucose tolerance test (GTT) is performed after a 10-12 hour fast. The fasting plasma glucose is measured, and then 75 g glucose solution is drunk in not more than 5 minutes, and the 2-hour plasma glucose measured. Patients may not smoke, eat nor drink anything other than water during the test, and should not perform any exercise. Gestational diabetes (GDM) is defined by either a fasting plasma glucose value ≥ 5.5 mmol/L and/or a 2-hour value ≥ 8.0 mmol/L. Abnormal tests are notified by pathology to the diabetes nurse educator, who will contact the women to arrange further management.
  
  

High-risk patients

• Women at special risk of GDM (e.g. previous GDM, fetal macrosomia, polycystic ovarian syndrome, strong family history, glycosuria) should be tested with a GTT in the first instance. If a GTT is performed before 24 weeks and is normal, it should be repeated at 28 weeks.

• Women who have had GDM in a previous pregnancy should have a GTT at their second antenatal visit. If this shows GDM, they are managed as outlined below. If normal, the GTT should be repeated at 28 weeks gestation.

First visit after diagnosis

Education

• All women with GDM are seen initially by the diabetes nurse educator and receive the following information:
  

Diabetes clinic

• All women with GDM are seen at the diabetes clinic by an obstetrician. In some circumstances (e.g. other complications, multiple pregnancy) it may be appropriate for them to remain with their original team and be seen in consultation as necessary by the diabetes team.

• All women with GDM will be seen by the dietitian and have appropriate dietary advice.

• If the glycaemic control is poor, women will also be seen by the diabetes physician.

Investigations

• HbA1c

• Urea, creatinine, uric acid and electrolytes

• Random plasma glucose

• Ultrasound examination at 30 weeks for growth. This should be repeated as clinically indicated, or at 36 weeks if the initial estimated fetal weight is >80th percentile.

Glycaemic control

• All women with GDM will perform home blood glucose monitoring, initially 4 times each day before breakfast and 2 hours after each meal.

• The target levels are ≤ 5.0 mmol/L fasting and < 6.7 mmol/L 2 hours after meals

• Initially all women are treated with dietary and exercise advice. If this fails to achieve the targets, they should be reviewed by the dietitian. If the targets are still not met, insulin therapy should be commenced.

• Occasionally, it may be appropriate to commence insulin on the basis of developing fetal macrosomia.

Subsequent visits

Frequency of visits

• Three-weekly until 28 weeks, then 2-weekly until 38 weeks then weekly until delivery if not on insulin. Women receiving insulin should be seen weekly from 34 weeks.

• Visit frequency should be increased if there are other complications, such as:

Fetal surveillance

• Ultrasound examination for growth as above. More frequent ultrasound examination, including umbilical artery blood flow measurement, may be indicated with the above complicating factors:

• Cardiotocography should be performed weekly from 40 weeks gestation in the absence of complicating factors.

• Earlier and more intensive fetal monitoring (more frequent CTG, Doppler flow studies, biophysical profiles) may be indicated in the presence of the above complications.

Delivery

• In patients with optimal glycaemic control and no complicating factors (see above) delivery should be considered at 40-41 weeks, with the method depending on obstetric factors. Insulin by itself is not an indication for earlier delivery. If an elective Caesarean section is to be performed, this should be at 39 weeks.

• Patients with one of the complicating factors mentioned above should be delivered at 38-39 weeks, or earlier if indicated. Elective Caesarean section should be performed at 38 weeks.

• If the estimated fetal weight at the time of delivery is <4,000 g, vaginal delivery is usually appropriate unless there are other obstetric indications for caesarean section.

• If the estimated fetal weight at the time of delivery is >4,250 g, elective caesarean section should be strongly considered because of the risk of shoulder dystocia.

• If the estimated fetal weight at the time of delivery is 4,000 - 4,250 g, the decision about the route of delivery should be discussed with the patient taking into account the risks for the particular patient.

Follow-up

GTT

• Women with GDM should have an appointment made for a postpartum GTT prior to postnatal discharge. This can be arranged antenatally from 36 weeks’ gestation. They do not need an appointment for routine postnatal review by the diabetes clinic.

• This GTT should be performed 6-8 weeks postpartum

• The GTT is a standard 75g GTT using WHO non-pregnant criteria

• Women with an abnormal GTT (diabetes, impaired glucose tolerance or impaired fasting glycaemia) should be reviewed by the diabetes physician. They should have annual GTTs thereafter.

• Women with a normal postnatal GTT should be advised about a healthy lifestyle, and to have a GTT every 2 years.

References