It is not possible to cover all aspects in a short article, but GPs need to know their way around this difficult topic.
Although there is no consensus on the definition of gestational diabetes mellitus (GDM), it can be defined as carbohydrate intolerance of variable severity with onset or first recognition during pregnancy.
GDM may include women whose glucose tolerance reverts to normal after delivery, or previously undiagnosed cases of type-1 or type-2 diabetes. If pre-existing type-1 or type-2 diabetes is diagnosed when a patient presents with pregnancy, intervention may be urgent.
There is a lack of evidence for routine screening for diabetes in pregnancy. However, in practice, dispstick testing for glucose takes place at each antenatal visit. An oral glucose tolerance test may be required.
GDM is associated with an increased risk of induction of labour, assisted delivery, caesarean section, macrosomia (large baby), neonatal hypoglycaemia and jaundice, respiratory distress, stillbirth, brain, spinal cord and cardiac defects and sacral agenesis.
Patients who develop GDM are more likely to have a recurrence in subsequent pregnancies, but lifestyle modifications such as dietary changes and weight loss can minimise risk.
Management of GDM
Impaired glucose tolerance is associated with macrosomia. Diet with or without insulin can reduce birth weight, but intensive treatment may compromise babies that are not macrosomic.
If pre- and post-prandial glucose levels remain normal and fetal growth is not excessive, then the pregnancy can be managed as normal.
Pre-eclampsia, miscarriage, and preterm labour are more common in women with pre-existing diabetes, and diabetic retinopathy can worsen rapidly during pregnancy.
NICE guideline 63 Diabetes in Pregnancy and the SIGN guideline on diabetes in pregnancy are useful references for care during and after pregnancy associated with diabetes.
The safety of medications before and during pregnancy has been reviewed in the latest NICE guideline, which states:
- Metformin may be used before and during pregnancy, as well as or instead of insulin, if the likely benefits from improved glycaemic control outweigh the potential for harm.
- Data from clinical trials and other sources do not suggest that the rapid-acting insulin analogues (aspart and lispro) adversely affect pregnancy or the health of the fetus or newborn baby.
- Evidence about the use of long-acting insulin analogues during pregnancy is limited. Isophane insulin is the first-choice during pregnancy.
It is also suggested that before or as soon as pregnancy is confirmed:
- Stop oral hypoglycaemic agents, apart from metformin, and start insulin if required.
- Stop ACE inhibitors and angiotensin-II receptor antagonists and consider alternative antihypertensives.
- Stop statins.
The best outcomes are achieved by maintaining excellent glycaemic control before and during pregnancy, but type-1 diabetes is a high-risk situation for mother and fetus.
Ketoacidosis, severe hypo- glycaemia, and rapid progression of microvascular complications can all occur. Obstetric complications and maternal infection are all more frequent.
Although type-2 diabetes is not common during a woman's reproductive years, the same intensive programme of metabolic, obstetric and neonatal supervision should be followed for these patients. One of the most important factors is the input of an experienced multidisciplinary team led by a named obstetrician and physician.
Preparing for pregnancy
Ideally, the pregnancy should be planned and pre-pregnancy counselling provided.
There should be a review of the medical, obstetric and gynaecological history; advice on glycaemic control to optimise HbA1c; blood glucose monitoring four to six times a day (target levels between 4 and 7mmol/l); intensive insulin regimes; and screening for complications.
A high complex-carbohydrate intake and low saturated fat intake are advised, and folate supplements should be given to reduce neural tube defects.
Because of the risk of rapid deterioration of diabetic retinopathy, regular fundal examination is advised.
If there is a pre-existing nephropathy (microalbuminuria or albuminuria) there may be a poorer pregnancy outcome, particularly with regard to worsening hypertension or pregnancy-induced hypertension and pre-eclampsia.
A deteriorating nephropathy and pre-eclampsia are the commonest causes of pre-term delivery.
If hypertension is a problem methyl-dopa, labetalol and nifedipine may be considered, but ACE inhibitors should not be given because of possible adverse effects.
Fetal monitoring is clearly essential. A combination of techniques is probably best.
Ultrasound is used, as in all pregnancies, to assess gestational age, fetal normality, growth and position.
In the third trimester as a minimum there should be weekly clinical assessment and regular cardiotocography, use of ultrasound if indicated, and mothers should report any reduction in fetal movement.
It is generally agreed delivery should be no later than 40 weeks. Delivery should be in a consultant-led maternity unit with continuous electronic fetal monitoring, neonatal intensive care facilities. IV insulin and dextrose are used to maintain optimal blood glucose levels.
An estimated fetal weight of more than 4.5kg is an indication for elective caesarean section.
Neonatal hypoglycaemia (<2.6mmol/l) must be checked for, because it is associated with adverse neuro-developmental problems in the short and long term. Early feeding can help to avoid this situation.
Breastfeeding results in lower fasting plasma glucose levels in type-1 diabetes than in those who are bottle fed. Mothers with type-1 or type-2 diabetes may require adjustment of their treatment regimen postnatally.
- Dr Barnard is a former GP in Fareham, Hampshire.
- GDM can be defined as carbohydrate intolerance of variable severity with onset or first recognition during pregnancy.
- Metformin may be used before and during pregnancy, as well as or instead of insulin.
- Women who have GDM have an increased risk of developing type-2 diabetes in the future.
- Women and their carers need to know how to recognise hypoglycaemia and ketoacidosis, and know who to contact in an emergency.